The structural properties of LaCu 6−x Au x have been studied using neutron diffraction, x-ray diffraction, and heat capacity measurements. The continuous orthorhombic-monoclinic structural phase transition in LaCu 6 is suppressed linearly with Au substitution until a complete suppression of the structural phase transition occurs at the critical composition, x c = 0.3. Heat capacity measurements at low temperatures indicate residual structural instability at x c that extends well into the orthorhombic phase. The instability is ferroelastic in nature, with density functional theory (DFT) calculations showing negligible coupling to electronic states near the Fermi level. The data and calculations presented here are consistent with the zero temperature termination of a continuous structural phase transition suggesting that the LaCu 6−x Au x series hosts an elastic quantum critical point.
Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200 -300 µV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of ∼ 1×10 19 -6×10 19 cm −3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 µV/K for a doping range 1×10 19 -3.5×10 19 cm −3 . Given that the lattice thermal conductivity in this phase has already been measured to be extremely low (∼ 0.7 W/m-K at 300 K), 1 our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.
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