Structural, transport and collosal dielectric properties

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Structural, transport and collosal dielectric properties of A-site substituted La2NiO4 To cite this article before publication: Mohd Saleem Malla et al 2018 Mater. Res. Express in press https://doi.org/10.1088/2053-1591/aaecf7

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Structural, transport and collosal dielectric properties of A-site

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substituted La2NiO4

M. Saleem, Diksha, A. Mishra and D. Varshney

Materials Science Laboratory, School of Physics, Vigyan Bhawan, Devi Ahilya University, Khandwa Road Campus, Indore 452001, India.

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Abstract: A-site substituted nickelates of the type La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) prepared via solid state reaction route are reported. X-ray diffraction (XRD) data analysis confirms the type of phase and structure of synthesized samples. All the samples were found to have

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crystallized into the tetragonal structure (I4/mmm). The XRD results were further verified using Rietveld refinement technique and tetragonal structure with space group (I4/mmm) was confirmed for all the prepared samples under investigation. The single phased tetragonal lattice structure formation was also confirmed from Raman scattering spectroscopy via stretching modes of vibration

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displayed by the prepared nickelates around 440 cm-1 and 220 cm-1. The elemental composition was verified using EDAX technique while FESEM images revealed the porous nature and heavy agglomeration. The dielectric studies confirmed the collosal dielectric constant with lowered loss values in the frequency range of 105-106 Hz with retained dielectric constant in the range of 103-104 at 106. The low temperature four-probe dc resistivity measurement revealed the samples are

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semiconducting in nature.

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Keywords: Nickelates; Structure; Retvield refinement; dielectric properties. *Authors

correspondence address: [email protected]

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1

Introduction

Oxides with colossal dielectric constant (CDC), inherit enormous scientific and technological value as they are considered to be the potent members to find their use in the advanced electrical energy

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storage i.e. charge storage devices [1]. Among these oxides, the K2NiF4-type exhibit interesting electrical and magnetic properties due to which they have attracted the researchers for their use in solid oxide fuel cells as electrode materials (SOFCs), oxygen separation membranes, high-Tc superconductors, substrates for thin films of high-Tc superconductors and lasers [2-5].

La2NiO4 systems have been identified as promising cathode materials that have capability to

replace the high temperature electrode materials in the lanthanum manganite perovskite family.

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Despite their coefficient of thermal expansion (CTE) comparable to electrolytes, they exhibit a mixed ionic and electronic conduction character. However, low electronic conductivity of La2NiO4 is still an issue that demands effective address [1-6]. La2NiO4, a perovskite-derived from K2NiF4-

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type mixed ionic–electronic conductor, shows high oxygen transport across a large temperature range and is an important candidate in SOFC cathode materials [7]. Structurally, La2NiO4+δ is a member of the Ruddlesden-Popper family with tetragonal crystal structure (space group I4/mmm) and consists of alternating LaNiO3 perovskite-like layers and possess "La2O2" rocksalt-like layers in

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an arrangement of offset ABA'B'. In this type of structure, the equatorial oxygen sites lie within the perovskite plane while as axial sites bridge the layers. Incorporation of interstitial oxygen within the rocksalt layers is remarkably facile, and affords a considerable range of oxygen hyper stoichiometry (δ) for SOFC applications [8, 9].

In recent years, so many materials of K2NiF4 type have been prepared and in the thirst for new giant dielectric constant materials, the synthesis of modified K2NiF4+δ structure materials was

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essential [10-12]. Later some modified K2NiF4 materials were prepared which display excellent dielectric properties. In the same manner, the La2NiF4 materials were modified by doping, doping concentrations, type of doping, calcination and sintering temperatures, preparation procedures etc. which all effected the nature of the La2NiO4 based materials [13-15]. Since La2NiO4+δ is a member

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of K2NiF4 family, it is therefore necessary to investigate the dielectric properties of modified La2NiO4 system.

Alkaline earth metal doped La2NiO4+δ has been studied [16] and were found to exhibit

colossal dielectric constant however, the basic physics underlying this CDC is still a mystery. Some researchers have related this conduct of CDC material to “charge glassiness” or polaron hopping

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while others have discussed it in terms of the Maxwell–Wagner relaxation induced by 2

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inhomogeneous charge distribution [13-17]. This CDC character of K2NiF4 type materials has been explained by means of [18] establishing the relationship among structural parameters, parameters related to polar-phonon modes, and dielectric nature. These materials display high dielectric constant

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well into the gigahertz range and many a times suffer from large frequency dispersion. These

properties in addition with low losses into the gigahertz range confirmed them to be the potent materials for capacitor applications [10-18].

As these materials seem to be promising materials, we have tried to modify this collosal

behaviour in the sense of doping parent La2NiO4 at A-site. We doped La2NiO4 by low concentration of Y and Ba to prevent any structural transition and explore the dielectric behaviour. We succeeded in the maintenance of higher dielectric constant with minimized loss. This article is focussed on the

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structural and dielectric properties in the light of dopants and their nature in addition to the effect of firing temperatures. From our current piece of work, we expect a little contribution in the said area

CDC.

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Experimental Details:

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by opening the window to go for new way doping with new featured properties in addition to the

The polycrystalline samples La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) were synthesized

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by the solid-state-reaction method. The starting materials were highly pure (>99.9%) powders of La2O3, NiO, Y2O3 and BaCO3. All the starting materials were used without pre-heating except La2O3 which was pre-heated at 600 oC for 6h to remove moisture. The oxides were weighed in stoichiometric ratios and mixed in an agate mortar. The mixture was calcined at 1050°C and 1150°C for 20h with intermediate grinding of 5h each. The polyvinlyalcohol was used as a binder for the so obtained powders which were pressed into pellets of the diameter of 10mm at a pressure of 7

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tonnes/inch under hydraulic press and sintered at 1300 0C for 24h. The pellets were cut into rectangular bars of length of 5mm and width of 1.1mm for four probe dc resistivity measurements. X-ray diffraction measurements of samples were carried out with CuKα1 (1.5406Å) radiation using Bruker D8 Advance X-ray diffractometer over the angular range 2θ (10°-90°) generating X-

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ray by 40kV and 40mA power settings. Rietveld refinement was done by Software Fullprof. Morphology studies have been carried using field emission scanning electron microscope (FESEM) instrument of mode SUPRA 55 having resolution of 1.4 nm at 1 kV without beam deceleration, magnification power range of x12 – 900000kVand acceleration voltage of 0.1 to 30kV and energy dispersive x-ray analysis (EDAX) were performed by energy-dispersive spectrometer, model INCA

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Oxford. Jobin Yuon Horiba LABRAM-HB visible (system HR800) spectrometer, with argon 3

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(488nm) as excitation source equipped with a peltir cooled charged coupled device detector was used for Raman spectroscopy in the range of 100 to 1200 cm-1. Fourier Transformation Infrared Spectroscopy (FTIR) was done by Perkin Elmer FT-IR/FIR spectroscopy in the range of 400 to 4000

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cm-1. The temperature dependence of resistivity for the samples La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) has been examined using conventional dc four probe method in the temperature range 35-300 K.

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Results and Discussions

3.1

Structural Analysis

The polycrystalline samples La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) ortho-nickelates

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were prepared via conventional solid state reaction route [19, 20]. The phase type and crystal structure was examined through the x-ray diffraction technique. The data so obtained has been

plotted and displayed in the Figure1. The analysis of the XRD spectra revealed that all the samples

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crystallized into the tetragonal structure with space group I4/mmm and all the peaks were in accordance with the JCPDS-00-011-0557 card. The phase has been retained for all the A-site doped La2NiO4 samples which is indicative of the uniform distribution of the dopants at their respective sites. The homogeneous dispersion is possible for the comparative ionic radii of the dopants and the

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respective parent sites i.e. [La3+ =1.061Å, Y3+=0.893Å, Ba2+=1.34Å and Ni2+=0.69 Å [21, 22]. The increase in the calculated lattice parameters of the doped samples compared to the parent sample is attribute to the higher ionic radii of the dopants [19- 22]. The intense characteristic peaks of the as prepared samples revealed the crystalline nature and narrowness of the FWHM is indicative of the larger crystallite size which was calculated using Scherer’s formula, t = kλ / βcosθ, where‘t’ is crystallite size, k = 0.9 called the shape factor, λ = 1.5406 Å, wavelength of the X-rays used, ‘β’ is

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FWHM and ‘θ’ is diffraction angle. The average crystallite size calculated was found 126.85 nm, 76.64 nm and 118.04 nm, for La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) respectively. The average crystallite size was further verified from the Retvield refined data and the values found were 129.05 nm, 79.11 nm and 113.21 nm for parent, Y3+ and Y3+/Ba2+ doped La2NiO4. The results are

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in close agreement with those obtained from the Scherer’s formula. The results achieved after the analysis of the X-ray spectra of the as prepared samples were further confirmed by fitting the data with the help of Rietveld refinement process using FullProf software [23]. The Rietveld refined data has been plotted and displayed in the Figure 2. The results obtained

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from the refinement confirmed the structure, type of phase, space group and various other parameters. The details of the refinements are given in the Table 1. The crystal structure of the 4

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pristine La2NiO4 sample under study has been depicted in Figure 3. In the Figure 3, it is clear that

3.2

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both Y3+ and Ba2+ have occupied the La-site while the octahedral Ni-site (NiO6) is unaffected.

Raman Scattering Studies

As a result of dark blackish colour of the samples, the data collection for Raman spectra of materials

was a difficult task by virtue of very strong light absorption. The photon energy is directly converted

into heat that leads to structural transformations [24]. Raman spectra of samples at room temperature in the energy region between 100 and 1200 cm -1 is shown in Figure 4 within the limits of which two

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peaks have been observed.

In tetragonal I4/mmm (D174h) symmetry 14 optic modes are expected assigned as 2Eg+2A1g+5Eu+4A2u+B2u. Out of these modes, 4 phonon modes namely 2Eg+2A1g are Raman active, 7 modes viz. 4Eu+3A2u are infrared active. Since the symmetry depends on the oxygen

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stoichiometry, we can modify it by sintering and laser heating [25]. For (La1-xSrx)2NiO4, the two Raman modes were observed at 450 cm-1 and 240 cm-1 assigned to the Ni-O stretching (A1g). However, in the present piece of work, these modes of vibration have been observed at ≈ 440 cm-1

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and ≈ 220 cm-1 confirming the tetragonal structure of the prepared samples. The slight shift may be due to doping concentration or may be due to preparation procedure and thermal effects [25, 26].

3.3

Compositional and Morphological Studies

The doped nickelates represented by the general chemical formula La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) have been verified for the composition using the energy dispersive X-ray analysis (EDAX) technique and the energy spectra obtained is displayed in the Figure 5. The close

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examination of these spectra reveals that within the limit of experimentation, there is no trace of foreign element in the samples under observation and all the comprising elements are present in the whole series. The composition of the compounds in the sense of presence of the elements and their concentration has been verified and the energy reflections are as per their concentration in the

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samples.

The micro-structure and hence morphology of the as prepared samples has been investigated

exploiting the most effective technique viz. field emission scanning electron microscopy (FESEM). The micrographs for the samples namely La2NiO4 and La1.95Y0.05NiO4 in the scale of 5µm are

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displayed in the Figure 6. The careful observation of the micrographs of the samples display the 5

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effect of high temperature sintering i.e. the average particle size has grown tremendously as a result of easy diffusion process facilitated by the extreme temperature treatment. It is clear from the micrograph of the samples of La2NiO4 that the grain growth trend is spherical and all the particles

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are well separated without any definite grain boundary. La1.95Y0.05NiO4 reveals the growth of the grains in the irregular shapes and displays the grain boundaries to some extent in addition to the heavy growth in the average particle size. All the prepared samples reveal agglomeration process

has taken place while sample preparation. Also all the synthesized samples displayed porous nature

which heavily influence the properties of the materials [27-30]. For the calculation of the average particle size, we used ImagJ software and the average size for La2NiO4 and La1.95Y0.05NiO4 were

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found to be 1.497µm and 1.327µm respectively. This huge growth in the average particle size are

believed to be the result of high temperature sintering which leads easy mass transport phenomenon.

3.4

Fourier Transform Infrared Spectra Analysis

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The FTIR spectra of the La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) have been displayed in the Figure 7 and data analysis revealed that in the parent and doped orthonickelate La2NiO4, two IR bands were observed corresponding at ≈648 cm-1 and ≈500 cm-1. These results confirm that all the prepared sample have K2NiF4 type structure. The band at≈ 648 cm-1 is attributed to stretching of Ni-

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O bond of NiO6 octahedron in the La2NiO4 based material that corresponds to E2u vibrational modes [31, 32]. The other strong band visible at ≈500 cm-1 is assigned to stretching vibrational mode of LaO-Ni bond and has been assigned to A2u vibration mode [33, 34]. In all these samples there is hardly any notable shift in the absorption band in the vicinity of ≈ 648 cm-1 and ≈ 500 cm-1 with dopant on A-site of the La2NiO4 which clearly indicates that the dopants are uniformly distributed corresponding to their sites of substitution. However, the intensity of the

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bands have increased slightly which may be attribute to the extent of porosity in the sample. Since there is slight variation in the lattice parameters in the Ba and Y substituted La2NiO4 compared to parent La2NiO4 and the structure is maintained over large doping concentration of x ≈ 0.5 in La2NiO4 and hence its antiferromagnetic insulator nature. Therefore, slight shift observed in IR peaks indicate

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stability of structure and nature of the as prepared samples [22, 35].

3.5

Four Probe dc Resistivity Studies

The temperature dependence of resistivity, ρ(T), of La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) ortho-nickelates was measured in the range of temperature from ≈30 to 300 K using

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conventional four-probe technique with and without magnetic field displayed in the Figure 8. In the 6

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absence of magnetic field, the extent of resistivity increases rapidly in the exponent shape as compared to that of presence of magnetic field. The behaviour displayed by the as prepared samples reveal the semiconducting nature in the whole range of temperature. In all the cases, we have

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observed that the resistivity in the presence of magnetic field is diminished to more than its half. This character may be attributed to the suppression of the scattering from lattice vibrations due to low temperature and the applied field as low temperature helps in the arrest of lattice vibrations and the magnetic field aligns the charge carriers. The conduction process for the semiconductors and insulators including the thermal activation can be successfully explained by the small polaron hopping, the variable range hopping models and thermal activation model also known as the bandgap (BG) model [34 -38].

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The resistivity behaviour is in accordance with the physical phenomena as the parent

La2NiO4 is antiferromagnetic insulator, it is certain that lower temperature will arrest lattice vibration responsible for any electron movement and increase in temperature will enhance lattice vibration

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and hence the electron movement resulting in the decrease of resistivity [16]. Since the prepared samples are insulating in nature, upto to certain extent of temperature the phonon motion is awakened and later the resistivity will remain constant as is shown by the samples. Close observation

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of the resistivity vs temperature plots for the synthesized samples reveals the increase in resistivity. This character is attributed to the increase in trap centers created upon doping. One more factor as revealed from the calculated parameters is the concept of lattice constants that represent the dimensions of the unit cell. If the doping leads in the increase of the lattice constant, volume of the cell increases and hence the number of charges per unit volume decreases which in turn increases resistivity. Based on this dielectric constant increases with increase in volume.

Dielectric Studies

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3.6

The aim of the current work is represented by the frequency-dependent dielectric constant confirming the collosal dielectric nature of the samples. The dielectric measurement has been given in the range of 105 Hz to 106 Hz. As is clear from the plots that the dielectric constant retains its higher value even after the frequency value of 1 MHz. The parent material La2NiO4 possesses a

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dielectric constant of 1.1x107 at a frequency of more than 105 Hz and retains a value of 5.5x104 at 1 MHz and is displayed as the inset of the Figure 9. It has been claimed that a charge-ordered nickelates retain their colossal magnitude larger than 104 into the GHz range and the reason for enhanced dielectric constant is possibly charge-order due to inhomogeneous charge distribution. Also the bond

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length variation at A-site may lead to the enhanced value of dielectric constant [39]. Although the 7

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extrinsic effects based on the inhomogeneous microstructures and the subsequent interfacial polarization, such as the Maxwell–Wagner effect, should contribute significantly to the giant dielectric response at lower frequencies, the high frequency giant dielectric response in the present

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material should originate from some intrinsic mechanisms since no extrinsic mechanism can be expected to be valid at such high frequencies [27].

The doped La2NiO4 display reduced values of the dielectric constant compared to the parent

one but in all the doped cases, the remnant dielectric constant after 1 MHz is still in the range of 104.

Since these materials are applicable to the gigahertz application, the lower retained dielectric constant in the present samples can be due to the porous nature of the sample as is clear from the

SEM images given above. The higher values of dielectric constant at lower frequencies and initially

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sharp decrease in the said value can be due to space charge polarization and could be explained via

Koop’s model and Maxwell–Wagner polarization theory [30, 41]. The slower change in the dielectric constant with increase in frequency can be attributed to the fact that beyond a certain

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critical frequency, the electronic exchange between the metal ions starts disobeying the applied field [39-41].

The dielectric loss (tan δ) as a function of log f (Hz) has been displayed in the Figure 10. The

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highest value of loss corresponds to the parent material La2NiO4. The low doping shows that loss value was effectively controlled and it approaches to a value of 1 at 1 MHz with higher retained value of dielectric constant exhibited by the samples at 1 MHz. The decrease in dielectric loss tangent with increase in frequency can be explained by Koop’s phenomenological model. The loss in the dielectric constant occurs when the polarization lags behind the applied alternating field. In addition to this, the dielectric loss arises also due to the presence of impurities and structural inhomogeneties

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[41, 42]. Table 2 represents the dielectric constants and losses at lower and higher frequency range.

Conclusion

The polycrystalline collosal dielectric ortho-nickelates with compositional formulae La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) were prepared through conventional solid state reaction route.

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The samples were found to have crystalized in tetragonal structure (I4/mmm) confirmed from XRD analysis followed by the Retvield analysis. The tetragonal structure was witnessed from Raman spectra analysis via stretching of Ni-O bond at ≈ 440 cm-1 and at ≈ 220 cm-1. The FTIR spectra analysis revealed Ni-O and La (Ba/Y)-O-Ni bonds in the synthesized nickelates which confirms the required sample formation. Despite the FESEM micrographs revealing porous nature, higher extent

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of agglomeration and rarely defined grain boundaries, these samples fulfil the criteria regarding 8

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structure and the dielectric nature. This character appeals that these if made compact may show modified dielectric properties. The parent La2NiO4 was found to exhibit dielectric constant in the range of 108 -107 in the frequency range of 105-106 Hz. The minimum doping concentration was

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found to reduce the dielectric loss to a considerable range with remnant dielectric constant of the

order of ≈105 about 1MHz. The temperature dependent four probe technique for dc resistivity measurement revealed semiconducting nature of the samples with sharp increase in the resistivity about 50K. The present materials with low loss, slow decrease in dielectric constant and stability at higher ac field demonstrates their usability in the Giga hertz applications.

Acknowledgements

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UGC-DAE-CSR, as an institute is acknowledged for providing characterization facilities.

Authors are thankful to Dr. V. Ganesan, Dr. R. Rawat for low temperature dc resistivity measurements, Dr. M. Gupta for XRD, Dr. Venkatesh and Dr. D. M. Phase for FESEM and EDAX

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characterizations. Also their guidance and useful discussions are worthy to acknowledge. Thanks to Mr. Lyantha, Mr. V. K. Ahire for their technical support. Authors pay special thanks to Dr. P.

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Sharma, School of Chemistry, Devi Ahilya University for providing FTIR facility.

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X. Weng, P. Boldrin, I. Abraham, S. T. Skinner, S. Kellici, J. A. Darr, J. Solid State Chem., 181

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C. C. Homes, T. Vogt, S. M. Shapiro, S. Wakimoto, and A. P. Ramirez, Science, 293, (2001) 673.

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[42]

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Figure Captions

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Figure 1: XRD spectrum La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) samples. Figure 2: Rietveld refinement of X-ray diffraction data for La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) nickelates.

Figure 3: Crystal structure of the pristine (a) La2NiO4 and (b) La1.9Y0.05Ba0.05NiO4 sample. Figure 4: Raman spectra of La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) samples.

Figure 5: EDAX spectra of La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) nickelates.

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Figure 6: FESEM micrographs of the prepared nickelates.

Figure 7: FTIR plots for the nickelates under investigation.

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Figure 8: Temperature dependent dc resistivity measurements of the prepared samples. Figure 9: Dielectric constant as a function of log f (Hz) for pristine and doped La2NiO4.

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Figure 10: Dielectric loss as a function of log f (Hz).

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Table 1 Table 1: Details of Rietveld refinements of La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) samples.

La1.95Y0.05NiO4

La1.90Ba0.05Y0.05NiO4

I4/mmm 3.851(2) 3.862(3) 12.686(3) 189.197(3) 6.945 9.96 13.70 53.0 44.6 30.4 2.158 1.5

I4/mmm 3.854(3) 3.85(2) 12.67(2) 188.25(2) 5.987 8.28 14.4 59.2 47.9 28.7 2.788 1.7

I4/mmm 3.857(2) 3.85(2) 12.69(2) 188.397(3) 6.887 7.92 12.2 54.5 42.9 27.1 2.509 1.7

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La2NiO4

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Parameters Space group a (Å) b( Å) c( Å) V (Å3) Density (g/cm3) RF RBragg Rp Rwp Rexp χ2 GOF

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Values of structural parameters obtained after Rietveld refinement

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At 1.25×105 Hz

At 1 MHz

La2NiO4

2.2x107

1.1x105

2

La1.95Y0.05NiO4

8.7x104

1.9x102

3

La1.90Ba0.05Y0.05NiO4

9.6x105

1.3x104

At1.25×105 Hz

At 1 MHz

87.1

3.83

5.52

1.04.

22.4

2.27

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1

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Table 2: Dielectric constant and dielectric loss values for La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) samples. Sr.No. Sample Name Dielectric Constant (έ) Dielectric loss Tan δ

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Figure 1

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La1.9Y0.05Ba0.05NiO4 La1.9Y0.1NiO4

40

50

2(degree)

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60

70

224 303208 310

118 220

215

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30

211 116 204 107 213

200

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110

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10

101

002

103

Intensity (a.u.)

La2NiO4

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Figure 2

Yobs Ycalc Bragg_position Yobs-Ycalc

Yobs Ycalc Bragg_position Yobs-Ycalc

La2NiO4

La1.95Y0.05NiO4

20

30

40

50

60

70

80

90

10

20

30

40

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2(degree)

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Intensity (arb. units)

Intensity (arb.units) 10

50

2(degree)

Yobs Ycalc Bragg_position Yobs-Ycalc

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Intensity (arb. units)

La1.90Ba0.05Y0.05NiO4

20

30

40

50

60

2(degree)

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60

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Figure 3:

(b) 3D-View for Y/Ba doped La2NiO4

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(a) 3D-View for La2NiO4

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438 cm

221 cm

-1

-1

Figure 4

La1.9Y0.1NiO4

600

La2NiO4

800

-1

Raman Shift (cm )

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400

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-1

438 cm

-1

225 cm

200

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437 cm

222 cm

-1

-1

Intensity (a.u.)

La1.9Y0.05Ba0.05NiO4

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1200

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Figure 5

La2NiO4

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La1.95Y0.05NiO4

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La1.9Ba0.05Y0.05NiO4

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Figure 6

L La2NiO4 a2NiO4

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La1.95Y0.05NiO4

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Figure 7

492.07 (A2u)

647.62 (E2u)

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637.76 (E2u)

1000

1500

2000

2500

dM

500

an

La2NiO4

646.5 (E2u)

488.56 (A2u)

La1.9Y0.1NiO4

496.23 (A2u)

% Transmittance

La1.9Y0.05Ba0.05NiO4

3000 -1

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Wavenumber (cm )

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Figure 8

1800

La2NiO4 (0T)

600

1200

500

1400

1000

400

1200

300

La2NiO4 (8T) 300

200

100

200 0

100

0

50

100

150

200

250

Temperature (K)

50

100

150

200

250

600

0 0

400

-200

300

50

100

0

50

100

2000

1000

150

La1.9Y0.05Ba0.05NiO4 (8T)

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Resistivity [ (-m)]

1200

1500

1000

800 600 400 200

0

500

-200

50

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0

0

50

100

150

150

200

Temperature (K)

200

Temperature (K)

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0

100

200

23

250

250

200

Temperature (K)

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1400

150

250

300

Temperature (K)

La1.9Y0.05Ba0.05NiO4 (0T)

2500

Resistivity [ (-m)]

400

200

Temperature (K)

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600

800

0 0

La1.9Y0.1NiO4 (8T)

200

300

0 -100

1000

800

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400

Resistivity [ (-m)]

Resistivity [ (-m)]

600

Resistivity [ (-m)]

1600

700

500

La1.9Y0.1NiO4 (0T)

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800

Resistivity [ (-m)]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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300

250

300

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Figure 9

7

1.2x10

6

1.0x10

La1.9Y0.1NiO4

7

1.0x10

La1.9Y0.05Ba0.05NiO4

5

6

8.0x10

6

5

4.0x10

5

2.0x10

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6.0x10

5

6.0x10

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Dielectric Constant (')

Dielectric Constant (')

8.0x10

6

4.0x10

0.0

5.0

6

5.2

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2.0x10

5.4

5.6

5.8

Logf (Hz)

6.0

La2NiO4

0.0

5.2

5.4

5.6

Logf (Hz)

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5.0

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5.8

6.0

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Figure 10

100

25

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La1.9Y0.1NiO4

La1.9Y0.05Ba0.05NiO4

20

Dielectric Loss (tan)

60

15

10

0 5.0

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5

40

5.2

5.4

20

La2NiO4

0 5.0

5.4

5.6

Logf (Hz)

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5.2

5.6

Logf (Hz)

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Dielectric Loss (tan)

80

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5.8

5.8

6.0

6.0