Sr2Nb2O7 is a very high-TC ferroelectric material with layered perovskite-type slab structure,
which undergoes successive phase transitions at about 1342 C, 215 C and ..156 C. High-resolution
Brillouin spectra of Sr2Nb2O7 single crystals have been stu...
Sr2Nb2O7 is a very high-TC ferroelectric material with layered perovskite-type slab structure,
which undergoes successive phase transitions at about 1342 C, 215 C and ..156 C. High-resolution
Brillouin spectra of Sr2Nb2O7 single crystals have been studied to observe the longitudinal acoustic
(LA) phonon modes in the temperature range from ..190 C to 400 C. The anomalous temperature
dependence of the LA phonon mode frequency corresponding to c22 elastic stiness coecient occurs
in the neighborhood of the normal-incommensurate phase transition temperature Ti (215 C). The
specic heat measured by MDSC showed an anomaly around 2142 C. The change in enthalpy and
entropy of the phase transition was estimated as 0.310.03 J/g and 1.50.2 mJ/g/C respectively.霆霆霆