Phase transitions of bulk and nanocrystalline La1−xSrxMnO3 (x = 0.35 and 0.37) perovskite manganite materials using in situ ultrasonic studies

La1−xSrxMnO3 perovskite manganite materials with two compositions, namely x = 0.35 and 0.37, both at bulk and nanoscale, were prepared by solid-state reaction and sonochemical reactor methods, respectively. The magnetic phase transition temperature of the prepared bulk and nanosamples was evaluated by in situ ultrasonic velocity and attenuation measurements. A home-made experimental setup was used for in situ measurement of ultrasonic velocities and attenuation over a wide range of temperatures (from 300 to 400 K). The observed anomalous lattice-softening behavior in the ultrasonic parameters was used to study the phase transition temperature (Curie temperature, TC), i.e., from paramagnetic to ferromagnetic phase, both in bulk and nanostructured perovskite samples. Further, the ultrasonic measurements confirmed that sharp and broad transitions occur in bulk and nanostructured perovskite manganite materials, respectively. The Curie temperature for nanostructured perovskite samples was lower than that for the corresponding bulk perovskite sample, which was clearly identified by ultrasonic measurements.

Graphical abstractThe temperature-dependent ultrasonic parameters show both normal and anomalous behaviors. The temperature at which the anomaly in velocity takes place is the Curie temperature (TC) of the perovskite sample. The anomalies that occurred in the velocities at 375, 371, 371, and 366 K are the TC for bulk La0.63Sr0.37MnO3 (BLSMO37), bulk La0.65Sr0.35MnO3 (BLSMO35), nano La0.63Sr0.37MnO3 (NLSMO37) and nano La0.65Sr0.35MnO3 (NLSMO35), respectively. It is observed that the TC value of NLSMO is lower than that of the corresponding BLSMO perovskite sample.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A sharp FM to PM transition for bulk La1−xSrxMnO3 perovskite samples. ► Absence of sharp FM to PM transition for nano La1−xSrxMnO3 perovskite samples. ► Study of nanostructured perovskite through observed anomalous at TC.