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 (0.5⩽x⩽0.87) 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 x≈0.75 in the CO state. It was particularly observed that a crossover of the Jahn–Teller vibration mode from Q2 to Q3 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.