Internal friction and Jahn-Teller effect in the charge-ordered La1-xCaxMnO3 (0.5≤x≤0.87)

The Jahn-Teller effect in the charge-ordered (CO) state for La1-xCaxMnO3 (0.5less than or equal toxless than or equal to0.87) was studied by measuring the low-temperature powder x-ray diffraction, internal friction, and shear modulus. We find that the electron-lattice interaction with the static Jahn-Teller distortion is the strongest near xapproximate to0.75 in the CO state. It was particularly observed that a crossover of the Jahn-Teller vibration mode from Q(2) to Q(3) near x=0.75 induces crossovers of the crystal structure from tetragonally compressed to tetragonally elongated orthorhombic, and of the magnetic structure from CE-type to C-type near x=0.75. The experimental results give strong evidence that the Jahn-Teller effect not only plays a key role in stabilizing the CO state, but also determines the magnetic and crystal structures in the CO state for La1-xCaxMnO3. (C) 2002 American Institute of Physics.