Metal insulator transition of bulk and nanocrystalline La_(1-x)Ca_xMnO_3 perovskite manganite materials through in-situ ultrasonic measurements

摘要

Bulk and nanocrystalline La_(1-x)Ca_xMnO_3 (x=0.75, 0.80 and 0.85) perovskite manganite samples were prepared by using the solid-state reaction and sonochemical reactor methods, respectively. The X-ray diffraction studies confirmed that the prepared bulk and nanoperovskite manganite samples were crystalline in nature with an orthorhombic crystal structure. The microscopic studies revealed that the particle sizes of the bulk and nanoperovskite samples were 0.75-0.90 |im and 120-160 nm, respectively. In addition, ultrasonic velocities and attenuations of the bulk and nanosamples were measured by using the in-situ ultrasonic through transmission method. The temperature-dependent ultrasonic parameters showed an interesting anomaly in both bulk and nanoperovskite samples. The observed marked softening and hardening in sound velocities or attenuation were related to metal-insulator phase transition temperature. In nanosamples, the metal insulator transition took place at a lower temperature compared with the corresponding bulk samples. The observed results confirmed that nanoperovskite samples have a broad transition compared with the corresponding bulk samples. The observed broad peak at transition temperature in nanoperovskite samples was used to confirm the nanocrystalline nature of perovskites.