Orientational disorder: A mechanism of amorphization at high pressure
Materials Science Division, Indira Gandhi Centre for Atomic
Research, Kalpakkam, 603 102, India
Accepted: 16 October 1998
Amorphization generally arises due to chemical disorder, high defect density or kinetic hindrances of equilibrium phase transitions. In this paper, we report that it can also be driven by orientational disorder of polyatomic ions or units. In potash alum, some of the sulphate ions are misoriented with their S-O bonds pointing towards potassium rather than towards aluminum, leading to an “orientational disorder” which ranges from 10 to 24%. Raman spectroscopic and X-ray diffraction studies reveal that samples with high initial orientational disorder exhibit a “reversible” amorphization at pressure around 60 kbar whereas those with low initial disorder exhibit an “irreversible” structural transition to a disorder-free crystalline phase.
PACS: 61.43.-j – Disordered solids / 64.70.Kb – Solid-solid transition / 78.30.-j – Infrared and Raman spectra
© EDP Sciences, 1998