Thermal properties of the pyrochlore, Y2Ti2O7

The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y2Ti2O7, have been determined over the temperature range 2 K⩽T⩽300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θD, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for Cp−Cv. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H0=34.69 kJ mol−1 and S(T=298.15 K)−S0=211.2 J K−1 mol−1. The thermal conductivity shows a peak at ca. θD/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y2Ti2O7 is 2.8 W m−1 K−1, close to the calculated theoretical thermal conductivity, κmin, for fully coupled phonons at high temperatures.