THE RELATIONSHIP BETWEEN THE COOPERATIVE JAHN-TELLER EFFECT AND THE INTERNAL FRICTION BEHAVIOR FOR THE CHARGE ORDERED La1-xCaxMnO3(0.50≤x ≤0.85)

The cooperative Jahn-Teller lattice distortion in the charge ordered (CO) state for La1-xCaxMnO3 (0.50≤x ≤0.85) was studied using the powder XRD and the internal friction. With decreasing temperature from the high temperature to the charge ordering transition temperature TCO , the shear modulus softens conspicuously; nevertheless, when the temperature is cooled below Tco, dramatic stiffening of the shear modulus driven by the development of the cooperative Jahn-Teller distortion was observed. The relative stiffening of the shear modulus △G/G varies with the Ca2+ concentration, and reaches the largest value at x-0.75. An internal friction peak appears at TCO, its height decreases with increasing measuring frequency and its position is frequency independent, showing a typical structural phase transition. The non-linear frequency dependence of the peak height can be fitted using the equation Qmax-1/Qmin-1=a×f-b.