Study of Phase Transformation in BaTe₂O₆ by in Situ High-Pressure X-ray Diffraction, Raman Spectroscopy, and First-Principles Calculations

Abstract

The title compound is synthesized by solid state reaction of a stoichiometric mixture of BaCO3 and TeO2 (air, 550 °C for 6 h, and 650 °C for 12 h).

Raman Fingerprint of Pressure-Induced Phase Transition in SnO2 Nanoparticles: Grüneisen Parameter and Thermal Expansion

“…The initial increase in intensity up to 8(6) GPa could be attributed to enhancement in the change of polarizability (∂χ/∂ q ) of different phonon modes (defect assisted) convoluted to form the broad band under the influence of pressure. However, the observed reduction of total intensity >8 GPa points to possible development of disorder at high pressure . In 4 nm NPs, decrease in intensity from 8 to 25 GPa is found to be 1.3 times.…”

“…Table 1 lists the pressure coefficients of all these modes of the ambient rutile phase. The normalized values of the pressure coefficient (dω/ ωdP) are also listed in Table 1 to have a reasonable comparison 30 of the pressure sensitivity of the different modes. A small value of the normalized parameter for the E g mode and larger values for the A 1g and B 2g Raman modes indicate that the A 1g and B 2g vibrational modes of SnO 6 octahedra are more sensitive to pressure, and the corresponding bonds can be deformed easily by pressure The modes in the high-pressure CaCl 2 -type phase (Figure 5b) continued to harden with pressure, similar to that observed for the ambient rutile phase.…”

“…However, the observed reduction of total intensity >8 GPa points to possible development of disorder at high pressure. 30 In 4 nm NPs, decrease in intensity from 8 to 25 GPa is found to be 1.3 times. On the other hand, in 2.4 NPs, the reduction in intensity in the same pressure range is 1.7 times; that is larger than the former one, indicating that defect density of this NPs increases significantly above 6 GPa.…”

“…A 4:1 methanol–ethanol mixture as the pressure transmitting medium and ruby balls as the pressure calibrant were loaded along with the sample. The 4:1 methanol–ethanol mixture used as a pressure transmitting medium in the diamond anvil cell is hydrostatic up to ∼10 GPa and solidified thereafter. − The results beyond 10 GPa can be considered as experimental under nonhydrostatic conditions, and that could be influenced by deviatoric stresses. − The influence of deviatoric stresses is noticed in the phase transition, metallization, and amorphization of samples, which often differ from the observation in pure hydrostatic conditions. ,− Beyond the hydrostatic pressure limit (>10 GPa), the positional disorder of the lattice can be due to deviatoric stresses which cause significant distortion to the crystal structure . Raman spectra of the sample in the DAC were collected by using 514.5 nm excitation line from an Ar-ion laser.…”

“…29,31−33 Beyond the hydrostatic pressure limit (>10 GPa), the positional disorder of the lattice can be due to deviatoric stresses which cause significant distortion to the crystal structure. 30 Raman spectra of the sample in the DAC were collected by using 514.5 nm excitation line from an Ar-ion laser. By use of a 20× long working distance objective, the spot size on the sample was about 1 μm.…”