Study of high temperature metal-insulator phase transition in La1−xCaxMnO3 employing in-situ ultrasonic studies.

Bulk La 1− x Ca x MnO 3 ( x =0.70, 0.75 and 0.90) perovskite samples were synthesized using solid state reaction technique. X-ray diffraction study on the sample indicates that the sample has single phase orthorhombic structure with a space group of pnma and has no secondary phase. By employing through transmission technique operated at a fundamental frequency of 5 MHz, ultrasonic velocities and attenuation were measured for both longitudinal and shear waves over a wide range of temperature from 300 to 700 K. The ultrasonic parameters showed an anomalous behavior at the transition temperature 640, 560 and 370 K for x =0.70, 0.75 and 0.90, respectively. These anomalies in the ultrasonic parameters were used to explain the second order metal-insulator phase transition. The existence of the single-ion magnetostriction in LCMO perovskite manganites is also revealed from the ultrasonic measurements. [ABSTRACT FROM AUTHOR]