Search results for "Structural phase"
showing 10 items of 12 documents
Pressure-dependent modifications in the optical and electronic properties of Fe(IO3)3: the role of Fe 3d and I 5p lone–pair electrons
2021
We have determined by means of optical-absorption experiments that Fe(IO3)3 is an indirect band-gap material with a band-gap energy of 2.1 eV. This makes this compound the iodate with the smallest band gap. We also found that under compression the band-gap energy has an unusual non-linear pressure dependence, which is followed by an abrupt and discontinuous decrease of the band gap at 24 GPa. The observed behavior is explained by means of density-functional calculations, which show that the behavior of the band gap is governed by the combined influence of Fe 4d and I 5p lone pair electrons. In addition, the abrupt decrease of the band-gap energy at 24 GPa is a consequence of a first-order s…
STRUCTURE AND PHASE TRANSITIONS IN [C(NH2)3]SbCl6 CRYSTALS
1998
Abstract The crystal structure of [C(NH2)3]SbCl6 at 298 K (monoclinic, C2/m) and 240 K (monoclinic, P21/a) has been determined. The structure consists of isolated SbCl6− anions and guanidinium cations. Differential scanning calorimetry, dilatometric and dielectric studies revealed two structural phase transitions; a first-order one at 351 K and a second-order one at 265 K. One of the two crystallographically non-equivalent anions, SbCl6−(1), disordered in the room temperature phase is postulated to contribute to the phase transition mechanism at 265 K. A ferroelastic domain structure is found below 351 K.
Lamb-Mössbauer factor in the spin crossover compound Fe(tpa)(NCS)2
1994
The Lamb-Mossbauer factor in spin crossover compounds has been the subject of controversial discussions in the literature. For several compounds, a significantly larger Lamb-Mossbauer factor for the complex molecules in the low-spin (fls) than in the high-spin (fhs) state has been reported, while for compounds studied in our laboratory such differences could not be observed. We prepared the compound Fe(tpa)(NCS)2, thef factors of which were reported to be very different. We could not prove thef factors of this compound to be different. The implications of a different structural phase of compound prepared by us are discussed.
High-pressure studies of topological insulators Bi2Se3, Bi2Te3, and Sb2Te3
2013
Bi2Se3, Bi2Te3, and Sb2Te3 are narrow bandgap semiconductors with tetradymite crystal structure (R-3m) which have been extensively studied along with their alloys due to their promising operation as thermoelectric materials in the temperature range between 300 and 500¿K. Studies on these layered semiconductors have increased tremendously in the last years since they have been recently predicted and demonstrated to behave as 3D topological insulators. In particular, a number of high-pressure studies have been done in the recent years in these materials. In this work we summarize the main results of the high-pressure studies performed in this family of semiconductors to date. In particular, w…
Dielectric and Elastic Parameters of LixNa1-xTa0.1Nb0.9O3 Ferroelectric Solid Solution Ceramics
2011
Results of the studies of electric and elastic parameters as functions of concentration in ferroelectric LiхNa1-хTa0.1Nb0.9O3 (x = 0–0.16) solid solutions and comparative studies of the elastic properties by acoustic and contact probe techniques are reported. The electric and elastic properties of LiхNa1-хTa0.1Nb0.9O3 solid solutions are shown to be rather sensitive to structural distortion at concentration-induced structural phase transitions. The values of elastic modules obtained from acoustic measurements are found to be in good agreement with those obtained by contact probe techniques.
The Ferroelectric Photo-Groundstate of SrTiO$_3$: Cavity Materials Engineering
2021
Significance Controlling collective phenomena in quantum materials is a promising route toward engineering material properties on demand. Strong THz lasers have been successful at inducing ferroelectricity in S r T i O 3 . Here we demonstrate, from atomistic calculations, that cavity quantum vacuum fluctuations induce a change in the collective phase of S r T i O 3 in the strong light–matter coupling regime. Under these conditions, the ferroelectric phase is stabilized as the ground state, instead of the quantum paraelectric one. We conceptualize this light–matter hybrid state as a material photo ground state: Fundamental properties such as crystal structure, phonon frequencies, and the col…
PHASE TRANSITIONS IN HALOGENOANTIMONATE(V) CRYSTALS: [N(CH3)4]SbCl6 AND [N(C2H5)4]SbCl6
1998
Abstract New crystals of the family of alkylammonium chloroantimonates(V), [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 , have been grown and systematically studied. X-ray studies show that [N(C 2 H 5 ) 4 ]SbCl 6 is composed of isolated cations and ideal SbCl 6 − octahedra. Differential scanning calorimetry, dilatometric and dielectric measurements reveal structural phase transitions in [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 of first order at 236 and 345 K, respectively. The measurements of 1 H-NMR spin-lattice relaxation times, T 1 , show that mechanism of the phase transitions in [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 is due to the reorientations of the tetraalkylammoniu…
Structural phase transition in [(C2H5)4N][(CH3)4N]ZnCl4
2019
The hybrid crystal [(C2H5)4N][(CH3)4N]ZnCl4 was studied using several experimental methods. DSC studies revealed the first order phase transition to the high temperature phase at about 496 K. This phase transition was confirmed in dielectric studies. Optical observation revealed the domain structure appearance characteristic for that of the phase transition between tetragonal and orthorhombic phases. This phase transition shows a lowering of symmetry as in the case of bromide analogs. Additionally, the optical studies showed the appearance of a number of cracks in the sample and in some cases, the samples became milky after cooling from the high temperature to the room temperature phase.
High-pressure structural investigation of several zircon-type orthovanadates
2009
Room temperature angle-dispersive x-ray diffraction measurements on zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three compounds we found evidence of a pressure-induced structural phase transformation from zircon to a scheelite-type structure. The onset of the transition is near 8 GPa, but the transition is sluggish and the low- and high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa. The equations of state for the zircon and scheelite phases are also determined. Among the three studied compounds, we found that ScVO4 is less compressible than EuVO4 and LuVO4, b…
Communication: Evidence of structural phase transitions in silicalite-1 by infrared spectroscopy
2013
The adsorption of trichloroethylene, perchloroethylene, and p-xylene on a MFI (Mobile-FIve) zeolite is studied using in situ FTIR spectroscopy at 298 K. Spectra of self-supported zeolites in contact with increasing pressures of pure gas were recorded at equilibrium in the mid-infrared domain. Analysis of the evolution of the shape and location of vibrational bands of the zeolite as a function of the amount adsorbed allowed the observation of structural modifications of the adsorbent for the first time by infrared spectroscopy.