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Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gmcl19

Electrical Behavior of Photoluminiscent Thionine/αZirconium Phosphate Intercalation Compounds a

Enrique Rodríguez-Castellón , Antonio Jiméneza

a

López , Pascual Olivera-pastor , Josefa MéRidaa

a

Robles , Francisco Pérez-Reina , Manuel a

Alcántara-Rodríguez , Fernando Souto-bachiller b

b

c

, Lolita Rodríguez-Rodríguez , Manuel Fortés & José Ramos-Barrado

c

a

Departamento de Química Inorgánica , Facultad de Ciencias, Universidad de Málaga , 29071, Málaga, Spain b

Departamento de Química , Universidad de Puerto Rico , Mayagüez, Puerto Rico, 00681-9019 c

Departamento de Física Aplicada , Facultad de Ciencias, Universidad de Málaga , 29071, Málaga, Spain Published online: 04 Oct 2006.

To cite this article: Enrique Rodríguez-Castellón , Antonio Jiménez-López , Pascual Olivera-pastor , Josefa MéRida-Robles , Francisco Pérez-Reina , Manuel AlcántaraRodríguez , Fernando Souto-bachiller , Lolita Rodríguez-Rodríguez , Manuel Fortés & José Ramos-Barrado (1998) Electrical Behavior of Photoluminiscent Thionine/αZirconium Phosphate Intercalation Compounds, Molecular Crystals and Liquid Crystals

Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 311:1, 269-274, DOI: 10.1080/10587259808042397 To link to this article: http://dx.doi.org/10.1080/10587259808042397

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Mol. Crysf. Liq. Crysr.. 1998. Vol. 3 11. pp. 269-274

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Electrical Behavior of Photoluminiscent Thionindu-Zirconium Phosphate Intercalation Compounds ENRIQUE ROD~GUEZ-cASTELLON", ANTONIO JM~NEZ-LOPEZ", PASCUAL OLIVERA-PASTOR', JOSEFA MI~RIDA-ROBLES', FRANCISCO PEREZ-REINA~, MANUEL ALCANTARA-ROD~GUEZ", FERNANDO SOUTO-BACHILLER~,LOLITA RODR~GUEZRODR~GUEZ~, MANUEL FORTES~,JOSE RAMOS-BARRADO" aDepartamentode Quimica Inorganica, Facultad de Ciencias, Universidad de Malaga, 29071 Malaga, Spain; bDepartamentode Quimica, Universidad de Puerto Rico, Mayaguez, Puerto Rico 0068 1-9019; 'Departamento de Fisica Aplicada, Facultad de Ciencias, Universidad de Malaga, 29071 Malaga, Spain

The self-aggregation of thionine in the interlayer of a-zirconium phosphate (a-ZrP) has been used to synthesize materials apt for the preparation of photosensitive thin films. The electrical behavior of the resulting intercalation compounds is reported here. Thionine forms by self-aggregation an array of straight chain polymers confined in the interlayer space of the metal phosphate. The a.c. conductivity behavior of three intercalation compounds, selected with thioninda-ZrP molar ratios of 0.22, 0.60 and 0.91, has been studied using impedance methods. These hybrid organic-inorganic materials display low activation energy values, 0.43, 0.39 and 0.30 eV, respectively, which are characteristic of electronic conductors. Keywords: thionine; intercalation; zirconium phosphate; conductivity INTRODUCTION

Previous studies have demonstrated that the luminescent properties of thiazine dyes, mainly thionine and methylene blue, can be significantly modified upon interaction with silicate hosts".21. More recently, we have reported that thionine forms monomolecular lamellar arrays by self-assembly in the interlayer region of a-zirconium phosphate, showing dye m e t a c h r ~ m a s y ~This ~ ~ . layered phosphate, denoted a-ZrP in the following, is a typical protonic conductorKS1, whose electrical conductivity originates on the external surface and is associated with its hydration degree: The presence of guest organic molecules hydrazine, diazines, and diazoles or substituted diazoles-in the interlayer region modifies the electrical properties of the phosphate with regard to both conductivity and activation energyI6]. In a recent paper1'], we reported the [677]1269

270/[678]

E. RODRIGUEZ

- CASTELLONel a / .

electrical behaviour of intercalation compounds prepared with thionine and a-tin phosphate. We concluded that these materials present electronic conductivity due to n,n-interactions between the aromatic structures, showing constant static permittivity and Davidson Cole parameters over a large temperature range. We extend now the study to include a series of compounds prepared by intercalation of thionine in a-zirconium phosphate.


MATERIALS AND METHODS The preparation and characterisation of the intercalation compounds were as previously describedi3]. Colloidal suspensions of n-propylammonium-a-ZrP were prepared as precursors for the intercalation of thionine"]. X-Ray diffraction patterns were registered on a Siemens D-501 diffractometer using monochromatic Cu-Ka radiation. Thermogravimetric and differential thermal analyses were carried out on a Rigaku Thermoflex analyzer using A 1 2 0 3 as the internal reference and a heating rate of 10 K min-'.Three samples, with low, medium and high thionine loadings, were selected to study the electrical properties of the intercalation compounds (Table I). TABLE I Composition of the thionine-a-ZrP intercalation compounds Sample

Formula

A.c. conductivity measurements were carried out with a computer-controlled Solartron 1260 operating at frequencies between 1Hz and SMHZ. Samples were placed on Pt electrodes as pellets, 13 mm diameter and 1 mm thickness, compacted at 6 h4Pa. D.c. conductivity measurements were done with a computer-controlled PAmeter/D.C. Voltage Source HP4 140B. Experimental data were corrected by the influence of connecting cables and other parasitic capacitances using a software correction program.

RESULTS AND DISCUSSION

The X-ray diffraction patterns (not shown) for the intercalation compounds showed two reflection lines at low loadings, one line at 14.67 A corresponding


TH ION INE/a-ZIRCON I UM PHOSPHATE ICS

[679]/271

to the precursor n-propylammonium phosphate, and a new line at 17.73 A corresponding to the intercalated phase. This new line increases with the thionine loading resulting in samples A and B (Table I) at high and intermediare loadings, respectively, showing only this line. Initially, at low loadings, the aromatic rings lie flat until the phosphate layers are densely covered. As the loading increases, the rings begin to slip over one another and stand more erect, expanding the layers, until a final arrangement is achieved with an inclination angle 8 = 40.4' measured with respect to the surface normal. The diffision of thionine begins at the edges of the crystals and proceeds with an advancing phase boundary toward the inside of the interlayer region. Thermogravimetric analysis of the intercalation compounds showed that they are thermally stable up to 300 'C. Below this temperature, the thermal decomposition of thionine was not observed, allowing to study the conductivity of these materials over a wide temperature range. All samples presented d.c. conductivities of the same order as that of a-ZrP (lo' Q-' cm-I). Table I1 lists d.c. conductivities at two different temperatures. The d.c. conductivity increases with thionine loading and temperature. The corresponding a.c. conductivity measurements were fitted to an equivalent circuit by a non-linear least squares method['] (Figure 1). The Nyquist plots at 465 K are similar['], presenting only a depressed semicircle (Figure 2). However, the modulus plots exhibit two or more semicircles, which can be associated with different relaxation processes (Figure 3). TABLE I1 D.c. conductivities for the thionine-a-ZrP intercalation compounds at 404 and 5b8 K

Sample

d.c. Conductivity(R-' cm-') 404 K

508 K

A

7' 10-6

7' 10'5

B

2.1o7

8.1O4

C

8.1O-*

2.9104

272/[680]

E. RODRIGUEZ

- CASTELLONet 01. R3

R2


RI

The Bode plots imply that the grain boundary resistance and the grain bulk resistance are very different, but the capacitances are similar. We have fitted an equivalent circuit composed by different associations, (6(RI (RzQz)(R3Q3)) in the Boukamp notation. R1 is related to the d.c. of the thionine intercalation compound, COis the geometrical capacitance, (R2Q2) is related to the grain boundary processes, and (R3Q3), which corresponds to the lowest relaxation frequency, is related to electrode processes. We find that the different parameters exhibit a strong dependence with thionine loading. For instance, R1 decreases when the thionine loading increases.

..:.

-

.*

70

ij

..

.. ..

ao 20

i

Sample C

FIGURE 2. 465 K. Nyquist plots for thionine-a-ZrP intercalation compounds


TH IONINE/a-ZIRCONIUM PHOSPHATE ICs

[6813/273

FIGURE 3. Bode plots for thionine-a-ZrP intercalation compounds

'?.,, 19

lo

1%

I2

I >

14

15

16

27

1mrr (K'I

FIGURE 4

Ahhrenius plot for electrical conductivity of samples A (A), B (0) and C ( )

Figure 4 shows the Arrhenius plots for d.c. conductivity. The activation energies 0 30, 0.39 and 0.43 eV for samples A, A, and C, respectively, increase inversely with the thioninc loading On the other hand, these values are much lower than those observed in intercalation compounds of a-ZrP with alkyl- and dialkyl amines (0.9 - 1.2 eV)'lO', where the conductivity is essentially protonic Therefore, it is inferred that the conductivity in the thionine-a-ZrP intercalates is due to delocalized electrons in the aromatic rings. A stronger interaction (i e. high thionine loading) between aromatic rings implies a lower value for the

E. RODRIGUEZ

274/[682]

- C A S T E L L ~ Neta/.


activation energy “‘I. On the other hand, the change of the d.c. intensity with time (not shown) permits to determinate the current due to electrons that is much higher than that due to other carriers. This means that the charge carriers are electrons rather than ions. Acknowledgements This work has been jointly supported by the Ofice of Naval Research (USA) and by the CYCIT (Spain). Illuminating discussions with Abraham Clearfield and Umberto Costantino are acknowledged with appreciation. References (a) C.B. Sunwar, and H. Bose, J ColloidalInterface Sci., 136, 54 (1990) and references therein. (b) R.A. Schoonheydt, and L. Heughebaert, Clay Minerals,27,91 (1992). G. Calzaferri, and N. Gfeller, J.Phys. Chem., 96, 3428 (1992). E. Rodriguez-Castellon, A. Jimenez-Lopez, P. Olivera-Pastor, J.M. Merida-Robles, F.J. Perez-Reina, M. Alcantara-Rodriguez, F.A. SoutoBachiller, L. Rodriguez-Rodriguez, and G.G. Siegel, Material Science Forum, 152-153,379 (1994). G. Alberti, M. Casciola, U. Costantino and F. Di gregorio, Solid Sate IO~CS 32-33, , 40 (1989). G. Alberti, M. Casciola and U. Costantino, in Solid Stute Protonic Conductors ll,Eds. J.B. Goodenough, J. Jensen and M. Kleitz (Odense University Press, Odense, Denmark, 1985). p. 215. M. Casciola, S. Chieli, U. Costantino and A. Peraio, Solid Stute Iunics, 46, 53 (1991). E. Rodriguez-Castellon, A. Jimenez-Lopez, P. Olivera-Pastor, J.M. Merida-Robles, F.J. Perez-Reina, M. Alcantara-Rodriguez, F. SoutoBachiller, L. Rodriguez-Rodriguez, M. Fortes, and J.R. Ramos Barrado, Solid Stute lonics, 9 7 , 2 17, (1 997) G. Alberti, M. Casciola, and U. Costantino, J Colloidlnterface Sci., 107,256 (1985). b) P. Maireles-Torres, P. Olivera-Pastor, E. Rodriguez-Castellon, A. Jimenez-Lopez, and A.A.G. Tomlinson, J. Muter. Chem., 1,739 (1991) J. Jonsher, Dielectric Relaration in Solids, Chelsea Dielectric Press 1993.

M. Casciola, U. Costantino, and F. Marmotini, Solid State lonics, 35, 67 (1989).

T. Kudo and K. Fueki, Solid Stute lonics, VCH Verlag, 1990.