Locally preservedα  →  βphase transition in natural radiation-damaged titanite (CaTiSiO₅): evidence from laser-induced photoluminescence and dielectric measurements

Abstract

In situ temperature-dependent laser-induced photoluminescence and dielectric measurements provide new evidence for the local occurrence of the α → β phase transition near 500 K in the preserved crystalline parts of natural radiation-damaged titanite (sample E2335 with ~24% amorphous fraction, containing Fe and Al impurities). Photoluminescence spectroscopic measurements show an anomaly in the vicinity of 500 K. The temperature-dependent evolution of the real part of the electrical conductivity (σ) and the real (ε') and the imaginary (ε″) part of the complex dielectric permittivity (ε ) of titanite have been measured at various AC frequencies (~1.2-96.8 kHz). Despite the masking and smearing effect of impurities and defects, the temperature-dependent behaviour of ε' and ε″ around the transition temperature of the investigated natural titanite E2335 shows a remarkable similarity to that of the synthetic end-member material (see Zhang et al (1995 Phys. Chem. Miner. 22 41-9)). This study indicates the suitability of photoluminescence and impedance spectroscopy for the detection of phase transitions, even in heavily disordered systems.

Analysis of temperature‐dependent Raman spectra of minerals: Statistical approaches

“…[48] It was noted that, in contrast to synthetic titanite, the stabilisation of the β-phase at room temperature is possible in natural samples due to structural disorder in the presence of impurities and/or radiation damage, which may suppress the phase transition near 500 K or prevent its identification. [69][70][71][72][73] We used statistical algorithms for processing titanite I(ν, T) data arrays to test the possibility of detecting a multistage displacive phase transition in a lowsymmetry crystal having a complex spectrum. Range I (100-400 cm −1 ), containing lattice and bending modes of SiO 4 tetrahedra, and Range II (400-980 cm −1 ; Figure 2c,f) of internal stretching vibrations of SiO 4 tetrahedra and Ti─O vibrations of TiO 6 octahedra were analysed.…”