Variation of ultrasonic behaviors in R_1/3Sr_2/3FeO₃ (R = La, Pr, Gd)

¹  Laboratory of Advanced Functional Materials and Devices, Department of Materials Science and Engineering, University of Science and Technology of China - Hefei, Anhui, 230026, PRC
²  School of Metallurgy and Resources, Anhui University of Technology - Maanshan, Anhui, 243002, PRC

Corresponding author: cfzhu@ustc.edu.cn

Received: 10 December 2008
Accepted: 7 May 2009

Abstract

The longitudinal ultrasonic velocity (V), as well as resistivity and magnetization has been measured in polycrystalline R_1/3Sr_2/3FeO₃ (R = La, Pr, Gd). When the R-site ion is changed from La to smaller-size R ion, the charge ordering (CO) transition shifts to lower temperature and finally disappears for R = Gd. Dramatic anomalies in V for the R = La, Pr compounds are observed near the CO transition temperature, which implies the electron-phonon coupling arising from the Jahn-Teller effect of Fe⁴⁺. And the theory calculation result shows that this coupling is weakened for Pr, which may lead to the shift of . In the case of Gd_1/3Sr_2/3FeO₃ with no CO transition, the anomaly in V is small, and may be attributed to the antiferromagnetic spin fluctuations. Below , another unexpected softening in V is discerned in La_1/3Sr_2/3FeO₃, while only a slope change is observed in Pr_1/3Sr_2/3FeO₃. This feature is attributed to the breathing-type distortion of Fe-O octahedron via the charge disproportionation, which is weakened in Pr_1/3Sr_2/3FeO₃.