Elastic anomalies associated with possible charge order and other transitions in mixed-valent YbPd

Elastic anomalies associated with possible charge order and other phase transitions in a mixed-valent compound YbPd were investigated by ultrasonic measurements. A pronounced elastic anomaly was observed at a possible charge-ordering temperature of 125 K, accompanied with a distinct hysteresis. On the other hand, a slight but clear elastic anomaly was observed at other phase transitions at 1.9 K and 105 K. We argue that the data can be described in terms of 4f low-lying level scheme of Yb ions under a crystalline electric field effct and a possible charge ordering although Yb seems to go into a mixed-valent state in YbPd.