Jahn-Teller effect and stability of the charge-ordered state in La1-xCaxMnO3 (0.5 <= x <= 0.9) manganites

Abstract

The longitudinal ultrasonic sound velocity and attenuation, the resistivity, and lattice parameters were studied as a function of temperature from 30K to 300K in La1−x CaxMnO3 (0.5 ≤ x ≤ 0.9). For all the samples, a dramatic stiffening of the sound velocity belowthe charge ordering transition temperature TCO was directly driven by distinct changes of the lattice parameters due to the formation of long-range ordering of Jahn-Teller– distorted MnO6 octahedra. The relative change of the sound velocity (ΔV/V) below TCO depends on the Ca 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 14T