Wide-temperature instability in high-T_c superconductors, La_1.85Ba_0.15CuO₄

Ultrasonic attenuation and velocity have been measured in the high-Tc superconductor La1.85Ba0.15CuO4 at 24 MHz. On cooling, a pronounced softening of the lattice is observed, beginning above room temperature. Below 200 K, the lattice remains soft and highly attenuating, suggestive of a near-instability state over the entire range 4 K to 200 K, partial stiffening occurs, but the attenuation remains higher than at room temperature, a feature suggestive of a possible glassy state. © 1987.