Thermodynamic properties of bismuth tellurites Bi2TeO5, Bi2Te4O11, Bi10Te2O19 and Bi16Te5O34

Abstract

The increasing importance and practical implementations of bismuth tellurites Bi2TeO5, Bi2Te4O11, Bi10Te2O19 and Bi16Te5O34 require sound knowledge on their thermodynamic properties like specific molar heat capacity (Cp,m), enthalpy (\(\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} H_{\text{m}}^{0}\)), entropy (\(\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} S_{\text{m}}^{0}\)) and Gibbs energy (\(- \Delta_{{{\text{T}}^{\prime } }}^{\text{T}} G_{\text{m}}^{0}\)). The specific molar heat capacities of the tellurites synthesized were measured experimentally, and their dependence on temperature was determined by the least squares method. The coefficients a, b and c in the equation: $$C_{\text{p}} = a + b \cdot T - c \cdot T^{ - 2}$$ were determined. The relative error between the experimentally determined specific molar heat capacity and the one calculated by the equation was found to be in the range 0.41–1.39 %. The coefficient of correlation (R) was close to unity for all the tellurites studied which indicated that the calculation method is adequate. The specific molar heat capacity (Cp,m), enthalpy (\(\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} H_{\text{m}}^{0}\)), entropy (\(\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} S_{\text{m}}^{0}\)) and Gibbs energy (\(- \Delta_{{{\text{T}}^{\prime } }}^{\text{T}} G_{\text{m}}^{0}\)) were calculated.