Orientational deformations leading to temperature-induced structural phase transition in Prehnite using Raman, Infrared, and Terahertz spectroscopy

Understanding molecular and structural properties of naturally extracted minerals under varying thermodynamic parameters such as pressure (P) and temperature (T) helps us to explore vital information regarding various geological processes. Here, we present the comprehensive results of Raman, infrared (IR), and Terahertz (THz) spectroscopic investigations on Prehnite (Ca2Al(AlSi3O10)(OH)2) mineral from ambient (25 degrees C) to 1000 degrees C in the 6.6 - 4000 cm-1 wide spectral range. The results indicate a substantial distortion in orientation between AlO6 octahedron and SiO4 tetrahedron layer leads to the strengthening of hydrogen bonds (HBs) in the Prehnite structure around 800 degrees C. Consequently, the disappearance of Raman active modes and abrupt change in fre-quency (omega) of Far-IR modes (obtained using THz spectroscopy) around 800 degrees C are spectral signatures of sym-metry change in the structure. Eventually, these orientational changes at the molecular level trigger structural phase transition around 800 degrees C, supported by X-ray diffraction (XRD) measurements. Thus, the present study depicts the pivotal role of inter-and intra-molecular interactions in Prehnite, which determines its bonding and structural characteristics and hence its physicochemical properties under diverse environments.