Charge-ordering correlated elastic anomalies in Nd1/3Sr2/3FeO3

The resistivity and longitudinal ultrasonic velocity have been measured as a function of temperature from 50 K to 300 K in the single-phase polycrystalline Nd1/3Sr2/3FeO3. At about 167 K (TCO), the resistivity shows sharp increase, corresponding to the charge ordering transition (CO). The velocity softens conspicuously as the temperature decreasing from 210 K and then stiffens dramatically below TCO. This feature is similar in character to that of charge-ordered La1/3Sr2/3FeO3, and implies strong electron-phonon coupling. This unusual elastic stiffening can be fitted by the mean-field theory, which hints the presence of the Jahn-Teller effect originating from the Fe4+. Below TCO, the different ultrasonic behaviors between Nd1/3Sr2/3FeO3 and La1/3Sr2/3FeO3 have been observed. The expected ultrasonic anomalies corresponding to the breathing type distortion are absent in Nd1/3Sr2/3FeO3. This feature is attributed to the unique feature of charge ordering transition in perovskite-type iron oxides.