Raman spectrum and the origin of phase transitions in quartz

Numerical analysis of atomic motion in the incommensurate phase of quartz (SiO 2 ) in the vicinity of phase transition

“…true β phase, is extrapolated to a certain pressuredependent temperature T x , that is several tens of K higher than T i at normal pressure. This peculiarity is in line with other experimental anomalies: deviation of the integrate Raman intensity from Curie-Weiss law [4] and the onset of specific heat [5], both detected within 30 K above T i . The second important unexplained issue is the existence of the acoustic displacement u z along the hexagonal z-direction in the observed modulated structure, which is not expected from the coupling between η and TA(C 66 ).…”

Long-period states of a crystal finite-size-particle system

“…Increasing P beyond the stability limit of the trivial solution gives rise to formation of a structure with period 77, whose amplitude increases with P, which results in the evolution of (b) and (c). For small amplitudes, i.e., in the sine mode, the structure is, quite accurately, described by (28) and, even to a higher accuracy, by (24) and (27). As the solution accuracy is increased, higher harmonics begin to play a larger role, and the sine mode transforms into that of domain walls (solitons) located in a commensurate four-period structure.…”

“…Reciprocal rotation of tetrahedrons plays an important role in the α-β-phase transition via the incommensurate phase and formation of acoustic properties in quartz in the vicinity of this transition [17][18][19][20]. In the course of analyzing the results obtained on quartz [25][26][27][28][29][30][31][32][33][34] an assumption was made concerning the existence of a relationship between the major effects and the rotational degrees of freedom [35,36].…”

Raman opalescence of a destabilizing soft mode near the phase transition in quartz monocrystals

“…Quartz crystals were extensively studied by means of Raman spectroscopy . First results concerning temperature dependence of Raman spectra in crystalline quartz were obtained in Landsberg and Mandelstam .…”

“…In Scott and Porto, thorough information on whole Raman spectra of this crystal has been obtained. Peculiarities near the phase transition point were studied in previous studies . Data on Raman line frequencies and half‐widths at various temperatures are presented in previous works .…”