Tin telluride: A weakly co-elastic metal

We report resonant ultrasound spectroscopy (RUS), dilatometry/ magnetostriction, magnetotransport, magnetization, specific-heat, and S 119 n Mössbauer spectroscopy measurements on SnTe and Sn_0.995 Cr _0.005 Te. Hall measurements at T=77K indicate that our Bridgman-grown single crystals have a p -type carrier concentration of 3.4× 1019 cm ^-3 and that our Cr-doped crystals have an n -type concentration of 5.8× 1022 cm^-3. Although our SnTe crystals are diamagnetic over the temperature range 2≤T≤1100K, 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 0.5μm distortion at T_c ≈ 85K. 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, θ_D, values of SnTe obtained from S 119 n Mössbauer studies show a hardening of phonons in the range 60-115 K (θ_D =162K) as compared with the 100-300 K range (θ_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 Δ C₄₄ / C₄₄ =A |( T-T₀ )/T₀ | ^-κ with κ=0.50±0.02, a value indicating a three-dimensional softening of phonon branches at a temperature T₀ ∼75K, 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.