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Temperature-dependent Raman spectroscopic study of ferroelastic K <sub/>2</sub> Sr(MoO <sub/>4</sub> )
摘要： Raman scattering measurements of K2Sr(MoO4)2 were performed in the temperature range of 25–750 ?C. The Raman spectrum of the low-temperature phase α-K2Sr(MoO4)2 that was obtained by first-principle calculations indicated that the Raman bands in the wavenumber region of 250–500 cm?1 are related to Mo–O bending vibrations in MoO4 tetrahedra, while the Raman bands in the wavenumber region of 650–950 cm?1 are attributed to stretching vibrations of Mo–O bonds. The temperature-dependent Raman spectra reveal that K2Sr(MoO4)2 exhibits two sets of modifications in the Raman spectra at ～ 150 ?C and ～ 475 ?C, attributed to structural phase transitions. The large change of the Raman spectra in the temperature range of 150 ?C to 475 ?C suggests structural instability of the medium-temperature phase β -K2Sr(MoO4)2.
关键词： ferroelastics,K2Sr(MoO4)2 crystal,phase transition,Raman spectroscopy
更新于2025-09-09 09:28:46
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Temperature Dependence of the Luminescence Spectra of a 5CB Liquid Crystal and its Phase Transitions
摘要： The spectroluminescence properties of 4cyano4'pentylbiphenyl CH3(CH2)4(C6H4)2CN (5CB) were studied in the temperature range 4.2–297 K. A red shift of the fluorescence spectrum was noted with increasing temperature. The long-wavelength shifts in these spectra were also analyzed. Comparison of the temperature dependence curves for the emission at the band maxima λmax and their halfwidths Δλ/2 in the fluorescence spectra and the results of a differential scanning calorimetry (DSC) study showed that phase transitions occur in the 5CB liquid crystals at ~230 and ~260 K.
关键词： liquid crystal,phase transition,differential scanning calorimetry,luminescence,low temperature,conformation change
更新于2025-09-09 09:28:46
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Charge-stripe crystal phase in an insulating cuprate
摘要： High-temperature (high-Tc) superconductivity in cuprates arises from carrier doping of an antiferromagnetic Mott insulator. This carrier doping leads to the formation of electronic liquid-crystal phases. The insulating charge-stripe crystal phase is predicted to form when a small density of holes is doped into the charge-transfer insulator state, but this phase is yet to be observed experimentally. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and realize the lightly doped charge-transfer insulating state of the cuprate Bi2Sr2CaCu2O8+x. In this insulating state with a charge transfer gap on the order of ~1 eV, our spectroscopic imaging scanning tunnelling microscopy measurements provide strong evidence for a unidirectional charge-stripe order with a commensurate 4a0 period along the Cu–O–Cu bond. Notably, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and formation of the Fermi surface. Our work provides fresh insight into the microscopic origin of electronic inhomogeneity in high-Tc cuprates.
关键词： spectroscopic imaging scanning tunnelling microscopy,electronic inhomogeneity,cuprates,charge-stripe crystal phase,high-temperature superconductivity
更新于2025-09-09 09:28:46