IJSRST162682 | Received : 12 Dec 2016 | Accepted : 20 Dec 2016 | November-December-2016 [(2)6 : 428-439] © 2016 IJSRST | Volume 2 | Issue 6 | Print ISSN: 2395-6011 | Online ISSN: 2395-602X Themed Section: Science and Technology 428 Effect of Multiple Metal Substitutions for A- and B-perovskite Sites on the Thermoelectric Properties of LaCoO 3 S. Harizanova 1 , E. Zhecheva 1 , V. Valchev 2 , P. Markov 1 , M. Khristov 1 , R. Stoyanova 1* * 1 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 2 Faculty of Physics, University of Sofia, 1164 Sofia, Bulgaria ABSTRACT The present contribution provides new data on the effect of multiple metal substitutions for A- and B-perovskite sites on the thermoelectric properties of LaCoO 3 -based ceramics. Two groups of perovskite comopositions are studied: double substituted cobaltates with general formula LaCo 0.8 M 0.1 M ’ 0.1 O 3 (M 0.1 M ’ 0.1  Ni 0.1 Fe 0.1 , Ni 0.1 Ti 0.1 , Mn 0.1 Fe 0.1 ) and Sr-containing cobaltate with La 0.9 Sr 0.1 Co 0.8 Ni 0.1 Fe 0.1 O 3 . The content of all magnetic (Ni, Fe and Mn) and diamagnetic (Ti and Sr) elements are chosen to be 0.10 mol. Structural and morphological characterizations are carried out by powder XRD, SEM and TEM analyses. The thermoelectric efficiency of the perovskites is determined by the dimensionless figure of merit, calculated from the independently measured Seebeck coefficient, electrical resistivity and thermal conductivity. The effectiveness of the multiple metal substitutions for improvement of the thermoelectric properties of LaCoO 3 -based ceramics is discussed. Keywords: Cobalt-Based Perovskites; Thermoelectric Oxides. I. INTRODUCTION A basic concept of thermoelectric materials is their ability to convert heat into electricity [1]. The thermoelectric efficiency is evaluated by the dimensionless figure-of-merit: ZT = S 2  T / k where S is the Seebeck coefficient,  and k denote electrical and thermal conductivity. Therefore, large Seebeck coefficient, large electrical conductivity and low thermal conductivity are simultaneously required to achieve high thermoelectric efficiency. As these three physical parameters are interrelated, developing of thermoelectric materials represents a scientific challenge [2]. That is why after a period of intensive studies performed in 1950-1960 the interest in such studies faded. But the research interest in these materials resurrected after 1997, the experimental finding of Terasaki [3] on layered sodium cobalt oxides having large thermopower contributing to this. As a result of intensive studies, both cobalt-based sulfides and oxides are considered as most suitable thermoelectric materials [4]. The more covalent character of the chemical bond for sulfides is responsible for their larger power factor even at room temperature. However, cobalt-based sulfides display poor chemical and physical stability under high temperatures and oxidizing conditions in comparison with that for oxides. Among oxides, three groups of cobaltates can be outlined: Na x CoO 2 with a layered structure; misfit Ca 3 Co 4 O 9 , with similar CoO 2 layers and LaCoO 3 with a perovskite structure. LaCoO 3 is one of the most interesting as a material with potential application in thermoelectricity due to its high Seebeck coefficient (S>500 V/K at room temperature) [5]. The transport properties of LaCoO 3 are determined (to a great extent) by the ability of Co 3+ ions to adopt low-, intermediate- and high-spin configurations in the perovskite structure, leading to an additional spin entropy effect [6,7]. However, the electrical resistivity is high (about 10 Ωcm at room temperature), which lowers the thermoelectric activity (ZT<0.01 at T=300 K). Therefore, the state-of- the-art research is mainly devoted to the enhancement of the thermoelectric efficiency of LaCoO 3 by single substitution for the La- and Co-sites [8,9]. Recently, we have demonstrated that multiple substitutions of Ni and Fe for Co in LaCo 1-x-y Ni x Fe y O 3 is a more effective way to improve its thermoelectric efficiency in comparison with single-substituted