Search results for "Phase Transition"

1985

Über die polymerisation bei der sublimation des trioxans. 17. Mitt. Über polyoxymethylene

1962

Bei der Sublimation von gereinigtem Trioxan und bei seiner Kristallisation aus der Schmelze erfolgt in der kristallinen Phase eine langsame Polymerisation zu hochmolekularem Polyoxymethylen. Die Ausbeuten an Polymeren sind um so hoher, je trockener das Trioxan ist und je geringer der Fremdgasdruck bei der Sublimation ist. Es wurde festgestellt, das diese Polymerisation durch Spuren von monomerem Formaldehyd ausgelost wird; wenn letzterer durch Silberoxyd zerstort wird, kann Trioxan unverandert sublimiert und kristallisiert werden. Wahrend der Polymerisation wird monomerer Formaldehyd von den wachsenden Polyoxymethylenketten abgespalten und so der Polymerisationskatalysator regeneriert. Desh…

On lead-scandium tantalate solid solutions with high electrocaloric effect

1992

Abstract The PbSc0,5Ta0,5O3 solutions are found to be a useful material for active elements of microcryogenic devices based on electrocaloric effect. A temperature difference of ΔT = 1. 0-1.8 K at field intensities 20–30 kV/cm in the interval of 210–310 K can be achieved by simultaneous or separate introducing of Sb and Co ions in B-sites of the lattice. The most important contribution to the electrocaloric effect is due to field-induced Fn3m → R3m phase transition in the case of high ordering of B-ions in the perovskite structure ABO3.

Investigations of the Microstructure of Lipid Interface Films

1990

The phase behaviour of phospholipid monolayers at electrolyte/gas interfaces is studied by fluorescence microscopy. At the LE/LC phase transition, phase separation leads to a Wigner-type lattice structure. The observations are quantified using digital image processing. The results show that the phase transition comprises three different regimes.

Structure and phase transition in (C2H5NH3)3Sb2Cl 9•(C2H5NH3)SbCl4; x-ray, DSC and dielectric studies

2000

Abstract The structure of (C2H5NH3)3Sb2Cl9 • (C2H5NH3)SbCl4 at 295 K has been determined. The crystals are orthorhombic, space group Pna21 (a -16.925(3), b = 24.703(5), c = 7.956(2) Å, V = 3326.4(12) Å3 , Z = 4, dc= 2.018, dm= 2.01(1) Mg m-3). They consist of an anionic sublattice composed of two different polymeric zig-zag chains. One is built of Sb2Cl9 3- units (corner sharing octahedra) and the other one is made of corner sharing SbCl5 2-square pyramids. In the cavites between the polyanionic chains four non-equivalent ethylammonium cations are located. Three of them are disordered. The cations are connected to the anions by weak N-H...Cl hydrogen bonds. A first order phase transition of…

Phase transitions and distortion of [BiCl6]3– octahedra in (C3H5NH3)3[BiCl6] – DSC and single-crystal X-Ray diffraction studies

2004

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the orde…

A strong electroweak phase transition from the inflaton field

2016

We study a singlet scalar extension of the Standard Model. The singlet scalar is coupled non-minimally to gravity and assumed to drive inflation, and also couple sufficiently strongly with the SM Higgs field in order to provide for a strong first order electroweak phase transition. Requiring the model to describe inflation successfully, be compatible with the LHC data, and yield a strong first order electroweak phase transition, we identify the regions of the parameter space where the model is viable. We also include a singlet fermion with scalar coupling to the singlet scalar to probe the sensitivity of the constraints on additional degrees of freedom and their couplings in the singlet sec…

High-Pressure Properties of Wolframite-Type ScNbO4

2022

In this work, we used Raman spectroscopic and optical absorption measurements and first-principles calculations to unravel the properties of wolframite-type ScNbO4 at ambient pressure and under high pressure. We found that monoclinic wolframite-type ScNbO4 is less compressible than most wolframites and that under high pressure it undergoes two phase transitions at ∼5 and ∼11 GPa, respectively. The first transition induces a 9% collapse of volume and a 1.5 eV decrease of the band gap energy, changing the direct band gap to an indirect one. According to calculations, pressure induces symmetry changes (P2/c–Pnna–P2/c). The structural sequence is validated by the agreement between phonon calcul…

Single crystal X-ray diffraction studies on [(CH3)nNH4–n]3[Sb2Cl9] (2,3) chloroantimonates(III) in their low-temperature ferroelectric phases—structu…

2005

The structures of two ferroic chloroantimonates(III): [(CH3)2NH2]3[Sb2Cl9] (DMACA) and [(CH3)3NH]3[Sb2Cl9] (TMACA) were determined in their low-temperature phases. The structure of DMACA was investigated at 100 and 15 K, and TMACA at 15 K. The structures consist of two-dimensional inorganic layers and organic cations bound together by the N(C)–H⋯Cl hydrogen bonds. All of the organic cations in both compounds at all studied temperatures are ordered. There is no indication of the structural phase transition in the structure of DMACA below 242 K. The geometry and distortions of the [SbCl6]3– octahedra in both compounds is discussed.

Structure and phase transitions in ethylenediammonium dichloride and its salts with antimony trichloride

2000

During the mixing of ethylenediammonium dichloride and antimony trichloride except of reported earlier [NH3(CH2)2NH3]5(Sb2Cl11)2 · 4 H2O a new salt [NH3(CH2)2NH3](SbCl4)2 was obtained. The crystals are monoclinic at 295 K, space group C2/m, a = 13.829(3), b = 7.408(1), c = 7.588(2) Å; β = 103.18(3)°; V = 756.9(3) Å3; Z = 2; dc = 2.585, dm = 2.56(2) g · cm–3. The structure consists of anionic sublattice built of Sb2Cl82– units composed of two SbCl52– square pyramids connected by edge. The ethylenediammonium cations are located in anionic cavities. The cations are disordered. Each methylene carbon atom is split between two positions. The X‐ray diffraction, DSC, TGA and dilatometric methods we…