Pergamon PII:S0022-3697(97)00003-6 J, Phys. Chem SolidsVol 58, No. 7, pp. 1033-1039, 1997 © 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0022-3697/97 $17.00 + 0.00 EFFECT OF COMPOSITIONS AND ANNEALING CONDITIONS ON THE PROPERTIES OF SOL-GEL PREPARED CALCIUM-MODIFIED LEAD TITANATE THIN FILMS M. L. CALZADAt, M. J. MARTINI', P. RAMOSt, J. MENDIOLAt, R. SIRERAt, M. F. DA SILVA:~ and J. C. SOARES§ i'Instituto Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain :~Institute Tecnol6gico e Nuclear, Departfimento de Fisica, Estrada National n 10. 2685 Sacav6m, Portugal §Centro de Fisica Nuclear da Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1699 Lisboa, Portugal (Received31 May 1996; acceptedin revised form 23 December 1996) Abstract--Sol-gel processing has been used for the preparation of calcium-modifiedlead titanate thin films with perovskite structure. The properties of the polycrystalline films have been studied as a function of the solution composition and the heating rate of the thermal crystallization treatment. The stoichiometry, crystallinity and microstructure of the films have been evaluated by Rutherford backscattering spectroscopy, grazing incidence X-ray diffraction analysis and scanning electron microscopy, respectively. The ferro- electric response of the filmswas determined by measurement of their hysteresis loops, in an attempt to relate electrical properties to processing conditions. © 1997 Elsevier Science Ltd. All rights reserved. Keywords: sol-gel, thin film, lead titanate, ferroelectricity. 1. INTRODUCTION Interest in ferroelectric lead titanate based thin films arises from their potential technological applications [1]. On heating from room temperature, PbTiO3 changes from a tetragonal to a cubic structural phase, undergoing a ferroelectric to paraelectric tran- sition at the Curie temperature of Tc ~ 490°C. The tetragonal phase is characterized by a large tetragonal distortion, c/a ,,d .06. This fact makes the poling of PbTiO3 materials difficult. If the Pb ion is substituted by another cation with the same valence but smaller size, such as Ca, a diminution of the c-axis of the tetragonal phase in the PbTiO3 occurs and a lowering of the Curie temperature Tc is produced [2]. As a consequence, the mechanical stability of the material increases upon cooling from the cubic to the tetra- gonal phase across the Curie temperature. In addition, a larger pyroelectric coefficient, dP/dT, is expected at room temperature due to the Ca-induced lowering of To, and high anisotropic piezoelectric coupling factors are measured in CaxPbl_xTiO3 ceramics, especially for a Pb/Ca ratio of 76/24 [3]. Thus, Ca0.24Pb0.76TiO 3 bulk ceramics have been used with success as an alternative material to PZT ceramics, especially for pyroelectric sensors and piezoelectric devices. Recently, Ca0.24Pb0.76TiOa thin films have been prepared and their piezoelectric, pyroelectric and ferroclectric properties tested, showing these thin films to also be of interest for applications such as microsensors or microactuators [4]. A number of techniques may be used for film fabrication. However, there is growing interest in alternative deposition processes based on sol-gel chemistry [5]. These offer good control over the chemical composition in multicomponent systems and low capital equipment expenditure. In essence, sol-gel processes for the preparation of films use spin- coating or dip-coating techniques to coat the substrate with an organic solution which contains the required ions. The as-deposited films are amorphous and non- ferroelectric. Therefore, postdeposition annealing treatments are required to crystallize the films into the ferroelectric perovskite structure. Insufficient con- trol of the properties of the sol-gel-derived solutions and of the thermal treatment used for crystallization may give rise to undesirable phases, perovskites con- taining defects and so on; all of which produce a deterioration in the ferroelectric properties of the films [6, 7]. In this paper we report results concerning the sol-gel preparation and characterization of Cao.24Pb0.76TiO3 thin films. Special emphasis is placed on the composi- tion of the precursor solution and other processing aspects that determine the final characteristics of the films, especially in relation to their ferroelectric response. 2. EXPERIMENTAL TECHNIQUES 2.1. Thin film preparation Solutions of calcium-modified lead titanate of nominal 1033