The longitudinal ultrasonic sound velocity and attenuation, the
resistivity, and lattice parameters were studied as a function of
temperature from 30 K to 300 K in La
1 − x
Ca
x
MnO3
(0.5 ⩽ x ⩽ 0.9). For all the
samples, a dramatic stiffening of the sound velocity below the
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
MnO
6 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 14 T.
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