Photo-induced high-temperature order-disorder phase transition in CaSnO3 perovskite revealed by Raman spectroscopy

TL;DR

This study reveals a photo-induced order-disorder phase transition in CaSnO3 perovskite, detectable via Raman spectroscopy and DSC, suggesting potential for optoelectronic and photocatalytic applications.

Contribution

The paper demonstrates a novel photo-induced phase transition in CaSnO3, linking Raman spectral changes to photo-excited ferroelectric order-disorder phenomena.

Findings

Raman frequency shifts and line width doubling at 121°C under specific laser excitation.

Phase transition observed with DSC but without strong order-disorder features.

Thermal expansion coefficients measured for CaSnO3.

Abstract

Calcium stannate perovskite (CaSnO3) has been studied by Raman spectroscopy at two excitation wavelengths (514.5 nm and 632.8 nm). A new first-order order-disorder phase transition induces Raman frequency shifts and line width doubling at 121C on heating (94C on cooling), seen in experiments using the 514.5 nm line of an Ar+-ion laser. The transition is also seen when using a 623.8 nm He-Ne laser and by differential scanning calorimetry (DSC), but without strong order-disorder character, indicating that the phase transition is dependent on photo-excitation. High-temperature powder X-ray diffraction measurements provide thermal expansion coefficients of ax = 13.9 x 10-6 K-1, ay = 2.7 x 10-6 K-1, az = 14.3 x 10-6 K-1. The phase transition is postulated to be associated with photo-excited charged and conductive nanoscale ferroelectric order-disorder. As such, CaSnO3 could represent the first in a new class of optoelectronic materials with additional potential photocatalytic properties.