Abstract
The longitudinal ultrasonic velocity ( V l ), as well as resistivity has been measured in single-phase polycrystalline La 1/3Sr 2/3Fe 1− x Mn x O 3 ( x = 0, 0.025, 0.05) at a frequency of 10 MHz, from 20 K to 300 K. It is found that with increasing Mn-doping level, the resistivity increases and the charge ordering transition temperature T CO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in V l above T CO and dramatic stiffening below T CO are observed. This abnormal elastic softening above T CO can be described well by the mean-field theory, which indicates that this feature is due to the electron–phonon coupling via the Jahn–Teller effect and this coupling is enhanced with the Mn doping. Below T CO, another softening in V l is observed for x = 0, and weakens with the increasing of Mn content. This character is attributed to the breathing-type distortion of Fe–O octahedron and suggests that the charge disproportionation (CD) transition is suppressed by the Mn substitution.
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