Thermal conductivity of (Er1−xYx)2Ti2O7 pyrochlore oxide solid solutions

The thermal conductivities of pyrochlore oxide solid solutions of general formula (Er1−xYx)2Ti2O7 with 0 ⩽ x ⩽ 1 have been determined for high-quality single crystals aligned along the [110] direction, over the temperature range from 3 to 300 K. Er2Ti2O7 and Y2Ti2O7 are isostructural and Er3+ and Y3+ are within 1% in size, but differ by a factor of about 2 in mass. Therefore, this system allows a clear test of the influence of mass of dopant on thermal conductivity, while controlling for other factors such as dopant size and sample purity. Although Y2Ti2O7 has a higher thermal conductivity than Er2Ti2O7 at T = 300 K, from 3 to 200 K their relative thermal conductivities reverse. Furthermore, we observe significant decrease in thermal conductivity upon doping Er2Ti2O7 with Y3+ ions, showing definitively that, in the temperature range from about 3 to 300 K, the impurity scattering effect of the lighter Y3+ ions is the predominant limiter of the thermal conductivity. This conclusion is supported by the finding that the phonon mean free path of the doped compounds decreases with increased dopant concentrations, increasing again as pure Y2Ti2O7 is approached.