Tin telluride: a weakly co-elastic metal

Abstract

We report resonant ultrasound spectroscopy (RUS), dilatometry/magnetostriction, magnetotransport, magnetization, specific heat, and ${}^{119}$Sn Mössbauer spectroscopy measurements on SnTe and Sn${}_{0.995}$Cr${}_{0.005}$Te. Hall measurements at $T=77$ K indicate that our Bridgman-grown single crystals have a $p$-type carrier concentration of $3.4\times 10^{19}$ cm${}^{-3}$ and that our Cr-doped crystals have an $n$-type concentration of $5.8\times 10^{22}$ cm${}^{-3}$. Although our SnTe crystals are diamagnetic over the temperature range $2\text{K}\le T\le 1100\text{K}$, the Cr-doped crystals are room temperature ferromagnets with a Curie temperature of 294 K. For each sample type, three-terminal capacitive dilatometry measurements detect a subtle 0.5 micron distortion at $T_c\approx 85$ K. Whereas our RUS measurements on SnTe show elastic hardening near the structural transition, pointing to co-elastic behavior, similar measurements on Sn${}_{0.995}$Cr${}_{0.005}$Te show a pronounced softening, pointing to ferroelastic behavior. Effective Debye temperature, ${\theta }_D$, values of SnTe obtained from ${}^{119}$Sn Mössbauer studies show a hardening of phonons in the range 60--115K (${\theta }_D$ = 162K) as compared with the 100--300K range (${\theta }_D$ = 150K). In addition, a precursor softening extending over approximately 100 K anticipates this collapse at the critical temperature, and quantitative analysis over three decades of its reduced modulus finds $\Delta C_{44}/C_{44}=A|(T-T_0)/T_0{|}^{-\kappa }$ with $\kappa =0.50\pm 0.02$, a value indicating a three-dimensional softening of phonon branches at a temperature $T_0\sim 75$ K, considerably below $T_c$. We suggest that the differences in these two types of elastic behaviors lie in the absence of elastic domain wall motion in the one case and their nucleation in the other.