Raman spectroscopic and X-ray diffraction study of α- and β-Mg2P2O7 at various temperatures

Raman spectra and X-ray diffraction patterns of Mg2P2O7 polymorphs (alpha- and beta-phase) were investigated at various temperatures up to 1073 K at ambient pressure. Typical Raman spectra and X-ray diffraction patterns were observed for the reversible phase transition between low-temperature alpha-Mg2P2O7 and high- temperature beta-Mg2P2O7 during heating and cooling. The effect of temperature on the Raman vibrations for the two Mg2P2O7 polymorphs was quantitatively analyzed. All the observed Raman active bands of the two Mg2P2O7 polymorphs showed linear temperature dependence with different slopes. The quantitative temperature dependences of the Raman bands are -4.01 x 10(-2) similar to 1.94 x 10(-2) and -2.31 x 10(-2) similar to -0.44 x 10(-2) cm(-1) K-1 for alpha- and beta-Mg2P2O7, respectively. The force constant evolution of [P2O7](4-) stretching vibrations and the temperature derivatives for both alpha- and beta-Mg2P2O7 were also determined. The thermal expansion coefficient of beta-Mg2P2O7 was estimated at 2.97(8) x 10(-5) K-1. Hence the isobaric mode Gruneisen parameters of beta-Mg2P2O7 were calculated. (C) 2022 Elsevier B.V. All rights reserved.