Pressure-induced structural phase transitions in natural kaolinite investigated by Raman spectroscopy and electrical conductivity
Meiling Hong, Lidong Dai, Haiying Hu, Xinyu Zhang
Abstract
Abstract We investigated the structural, vibrational, and electrical transport properties of natural kaolinite and its high-pressure polymorphs by Raman scattering and electrical conductivity measurements at 293–673 K and up to 10.0 GPa using diamond-anvil cell. Upon compression, kaolinite underwent two structural transitions from kaolinite I to kaolinite II to kaolinite III phases at pressures of 2.9 and 6.5 GPa, respectively, which was disclosed by the inflection point in the pressure-dependent Raman shifts and electrical conductivity. Upon decompression, kaolinite III directly transformed to kaolinite I at 0.8 GPa without the appearance of kaolinite II. Additionally, the influence of temperature on the structural transformation of natural kaolinite was explored by high-temperature and high-pressure electrical conductivity measurements and negative temperature-dependent transition pressure correlations were obtained. A phase diagram of natural kaolinite was established for the first time and the kaolinite I-kaolinite II and kaolinite II-kaolinite III phase transition boundaries were determined: P (GPa) = 4.298–0.00462 T (K) and P (GPa) = 8.895–0.00799 T (K), respectively. Furthermore, our acquired phase diagram can be applied to understand the stability field of high-pressure polymorphs of kaolinite in the Earth’s interior and may provide a phase transition model for other kaolin-group minerals.