Jahn-Teller effect and stability of the charge-ordered state in _x manganites

¹ Structure Research Laboratory, Department of Materials Science and Engineering University of Science and Technology of China - Hefei, Anhui, 230026, PRC
² Laboratory of Internal Friction and Defects in Solids, University of Science and Technology of China - Hefei, Anhui, 230026, PRC
³ Department of Physics, University of Hong Kong - Hong Kong, PRC

Corresponding author: lixg@ustc.edu.cn

Received: 22 May 2002
Accepted: 12 September 2002

Abstract

The longitudinal ultrasonic sound velocity and attenuation, the resistivity, and lattice parameters were studied as a function of temperature from 30 to 300 in _x . For all the samples, a dramatic stiffening of the sound velocity below the charge ordering transition temperature was directly driven by distinct changes of the lattice parameters due to the formation of long-range ordering of Jahn-Teller–distorted ₆ octahedra. The relative change of the sound velocity below depends on the concentration x and reaches the maximum at x=0.75, implying that the effective strength of the electron-lattice interaction with the Jahn-Teller distortion is the strongest at x=0.75 and hence the charge-ordered state is mostly stabilized near x=0.75 and insensitive to the application of a magnetic field, which is supported by the charge transport properties under high magnetic fields up to 14.