Thermal and Physical Properties of Perovskites

*Perovskite and Piezoelectric Materials*

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**112**

**Chapter 6**

**Abstract**

**1. Introduction**

**Figure 1**.

(**Figure 2**).

**115**

*Sergey Shornikov*

**Keywords:** perovskite, thermodynamics

system with unusual isotopic characteristics [3–5].

Thermodynamics of Perovskite:

Solid, Liquid, and Gas Phases

The present work is devoted to the review of experimental data on thermodynamic properties of perovskite in the condensed state, as well as the gas phase components over perovskite and its melts at high temperatures.

Calcium titanate (CaTiO3) or perovskite was found by Rose [1] in the Ural Mountains in 1839 and named after the Russian Statesman Count Lev Perovski. Perovskite is a relatively rare mineral, which is a promising material for use as matrices for safe long-term storage of actinides and their rare earth analogs that are present in radioactive waste [2]. It is of particular interest for petrology and cosmochemical research as a mineral which is a part of refractory Ca-Al inclusions often found in carbonaceous chondrites, which are the earliest objects of the solar

In addition to perovskite, two more calcium titanates, Ca3Ti2O7 [6] and Ca4Ti3O10 [7], melting incongruently, were found in the CaO-TiO2 system. The other calcium titanates, Ca4TiO6 [8], Ca3TiO5 [9], Ca8Ti3O14 [8, 10], Ca2TiO4 [9], Ca5Ti4O13 [11], Ca2Ti3O8 [6], CaTi2O5 [12, 13], CaTi3O7 [14], Ca2Ti5O12 [15], and CaTi4O9 [16], are mentioned in the literature. They also seem to be unstable, which does not exclude their possible existence [17]. Compiled in this paper on the basis of data [7, 18], as well as the results of recent studies by Gong et al. [19], the phase diagram of the CaO-TiO2 system in the high-temperature region is shown in

**2. The thermodynamic properties of perovskite solid phase**

Thermochemical data on perovskite [20–24] are based on calorimetric measure-

ments of entropy of perovskite formation Δ*S*298(CaTiO3), obtained by Shomate [25], and high-temperature heat capacity of perovskite *Cp*(CaTiO3) in the temperature ranges of 15–398 K [26], 293–773 K [27], 376–1184 K [28], 383–1794 K [29], and 413–1825 K [30]. The differences between the data do not exceed 5 J/(mol K) up to a temperature of 1200 K, but they are quite contradictory at higher temperatures
