Journal of Alloys and Compounds 388 (2005) 308–313 Microstructural characterization of sol–gel derived Pb 1-x La x TiO 3 ferroelectrics Jun Chen, Xianran Xing ∗ , Ranbo Yu, Jinxia Deng, Guirong Liu Department of Physical Chemistry, University of Science and Technology Beijing, Xueyuan Road 30, Beijing 100083, China Received 9 July 2004; received in revised form 30 July 2004; accepted 30 July 2004 Abstract The ferroelectrics Pb 1-x La x TiO 3 with good stoichiometry were prepared by a sol–gel route in the composition range from x = 0.0 up to 0.4 in 0.05 increment. The compounds were indexed in a tetragonal phase for 0.0 ≤ x < 0.25, and in a cubic phase for 0.25 ≤ x < 0.4. A tiny amount of pyrochlore phase La 2 Ti 2 O 7 was detected at x = 0.4. The ion oxidation states of solid solution compounds were characterized by X-ray photoelectric spectroscopy (XPS) and electron spin resonance (ESR). For the compounds Pb 1-x La x TiO 3 prepared in the atmosphere, the electrical neutrality is kept not by the reduction from Ti 4+ to Ti 3+ , but by the creation of cation vacancies in the A- and B-sites. The grain size of Pb 1-x La x TiO 3 increases with increasing La content. © 2004 Elsevier B.V. All rights reserved. Keywords: Pb 1-x La x TiO 3 ; X-ray powder diffraction; XPS; SEM; Valence fluctuations 1. Introduction Lanthanum doped lead titanate ceramics have emerged as highly promising materials for piezo-mechanical and py- roelectric applications due to their large electro-mechanical anisotropy in the coupling factors along and perpendicular to the direction of polarization and due to the large pyroelec- tric coefficient along the polarization axis [1,2]. These modi- fied materials can be applied in optical waveguides, infrared sensors, dynamic random access memories and non-volatile memories [3]. In general, these properties of lanthanum doped lead titanate materials mostly depend on the lanthanum concentration. One of the characteristics can be optimized by adjusting the molar ratio of Pb/La. For example, the solid so- lution compound Pb 0.9 La 0.1 TiO 3 (PLT10) shows a prominent pyroelectric effect [2,4], whereas Pb 0.72 La 0.28 TiO 3 (PLT28) possesses a strong electro-optic effect [5]. In the system of solid solution Pb 1-x La x TiO 3 (PLT), a re- duction of Ti 4+ to Ti 3+ or some vacancies in the cation sites must be produced in order to maintain electrical neutrality. ∗ Corresponding author. Tel.: +86 10 62334200; fax: +86 10 62333477. E-mail address: xing@ustb.edu.cn (X. Xing). In the fabrication process, several methods were employed to maintain electrical neutrality. For example, this kind of compounds can be prepared by creating cation vacancies in A-sites or in B-sites [6–8], or can be synthesized under a reducing atmosphere reducing Ti 4+ ions to Ti 3+ [9]. The properties of PLT are influenced not only by the vacancy concentration but also by the Ti 3+ concentration to a cer- tain extent. The local structural defects introduced by B-site vacancies have much more inhibiting effects on the macro- scopic cubic-to-tetragonal transition than the A-site vacan- cies, and the magnitude of net polarization in the PLT-B is smaller than in the PLT-A [6,7]. It is well known that the electrical neutrality could be compensated in both the A-site and the B-site, and the effects of the vacancies on the ferro- electric properties have been widely investigated. However, it has hardly been investigated whether the electrical neutral- ity can be partially compensated by the reduction of Ti 4+ to Ti 3+ in PLT compounds prepared in the atmosphere. To bet- ter understand the maintenance of electrical neutrality in the PLT system, the stoichiometry has to be taken into account. However, it is difficult to accurately control the stoichiome- try because of lead oxide volatilization at high temperature in the solid-state reaction process or in some film fabrication 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.07.038