Thermal properties of tetragonal ZrO2at low temperatures

Specific-heat (1.7-25 K) and thermal-conductivity (1.7-45 K) measurements are reported on ${\mathrm{Y}}_2$ ${\mathrm{O}}_3$-stabilized tetragonal Zr${\mathrm{O}}_2$. As in cubic Zr${\mathrm{O}}_2$, an Einstein-type excess specific heat (62 ${\mathrm{cm}}^{-1\mathrm{}}$) is found above 7 K, and the amplitude of this term agrees well with the oxygen-vacancy concentration (1.4%). A second excess specific heat below 5 K is found (as in the cubic form), due to the electric quadrupole moment of the hafnium impurity which contributes a Schottky term ($\delta =50\mathrm{}$ mK). The Debye temperatures obtained from the Einstein and Schottky fits are 515 and 507 K, respectively. As in the cubic form of Zr${\mathrm{O}}_2$, the thermal conductivity displays two glasslike features: (1) a plateau near 50 K and (2) a quadratic dependence, $K\sim {10}^{-5\mathrm{}}{T}^2$ W ${\mathrm{cm}}^{-1\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$ at the lowest temperatures. The accumulated evidence suggests that the oxygen conductivity and the low-temperature thermal properties of Zr${\mathrm{O}}_2$ are determined by the oxygen vacancies and are relatively insensitive to whether the host zirconia lattice is cubic or tetragonal.