Search results for "Phase Transition"
showing 10 items of 1281 documents
Solvent-mediated phase transformation between two tegafur polymorphs in several solvents
2014
This paper describes a study of the solvent-mediated polymorphic transformation (SMPT) of the metastable α tegafur to the thermodynamically stable β tegafur in several solvents. Phase transformation in acetone, ethanol, i-propanol, toluene, and water at 22 °C was described using the solid-state kinetic model P2; the rate constants for this process were in the range from 0.028 min−1 to 0.0056 min−1. In all of the employed solvents, an induction time was observed. Kinetic, solubility and scanning electron microscopy data indicated that nucleation kinetics corresponded to a second-order power function and according to the kinetic model, the nuclei growth rate was constant in the examined SMPT.…
Formation of local spin-state concentration waves during the relaxation from photoinduced state in a spin-crossover polymer
2017
The complex relaxation from the photoinduced high-spin phase (PIHS) to the low-spin phase of the bimetallic two-dimensional coordination spin-crossover polymer [Fe[(Hg(SCN)3)2](4,4′-bipy)2]nis reported. During the thermal relaxation, commensurate and incommensurate spin-state concentration waves (SSCWs) form. However, contrary to the steps forming at thermal equilibrium, associated with long-range SSCW order, the SSCWs forming during the relaxation from the PIHS phase correspond to short-range order, revealed by diffuse X-ray scattering. This is interpreted as resulting from the competition between the two types of SSCW order and another structural symmetry breaking, due to ligand ordering,…
Spin crossover star-shaped metallomesogens of iron(II).
2014
Three new types of spin crossover (SCO) metallomesogens of Fe-II based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris(2-aminoethyl)-amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1H-naphtho[2,3-d]imidazole (nim18) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic meas…
An EPR investigation of the phase transitions and cooperative ordering phenomena of pentaamminecopper(II) polyhedra in Cu(NH3)5X2 [X=BF4, CIO4; Br]
1996
The results of powder and single-crystal EPR studies on Cu(NH3)5X2 compounds [X=BF4, CIO4; Br] give evidence that phase transitions from a cubic α-phase (g i ≃2.12) with an anti-K2PtCl6 type structure to low-temperature β-phases with reduced symmetry occur, which are induced by ordering processes of the vacancies □ of elongated [Cu(NH3)5□]2+ pseudo-octahedra. The type of order is crucially controlled, by the nature of the anion. In the case of the BF 4 − and ClO 4 − salts the large anions are structure-determining leading to a slightly disturbed antiferrodistortive order of the elongated CuIIN5 square pyramids atT c≃155 K and <130 K, respectively. The resulting pseudo-tetragonal β-structure…
Neutron diffraction experiments on UCu4+xAl8−x
1992
Abstract Neutron diffraction experiments are reported on UCu4+xAl8−x for concentrations 0.1≤ x ≤1.9 and temperatures 1.6 K≤T≤300 K. For x ≤ 1 these compounds undergo antiferromagnetic phase transitions into a collinear AF I-type structure. with the magnetic moments aligned along the tetragonal c-axis and alternating order within the a−b planes. With increasing concentration the ordering temperatures decrease and moment compensation due to a Kondo-type interaction develops for x>1.
LaAg x In1?x
1980
The phonon dispersion of LaAg x In1−x (x=1, 0.89, 0.8) has been studied by inelastic neutron scattering in the cubic high temperature phase. A soft mode behaviour was observed at theM-point. The doubling and the cubic to tetragonal deformation of the elementary cell was observed through the phase transition. The measurements of the elastic constants were extended to 450 K and their magnetic field dependence was investigated.
Structure and properties of high piezoelectric coupling Pb(B′½Nb½)O3-PbTiO3binary systems
1999
Abstract The (1-x)Pb(Lu½ Nb½)O3-xPbTiO3 and (1-x)Pb(Er½ Nb½)O3-xPbTiO3 binary systems have been obtained, the structure and properties of which are studied. The unit cell of erbium niobate (PErN) is described as pseudomonoclinic of orthorhombic Bmm2 symmetry: a=c=4.2161 A b=4.0869 A β=90.55° and composition is characterized with antiferroelectric phase transition at 305°C. The PErNT system has the morphotropic phase region extending over the x=0.4–0.6 interval. In PLuNT ceramics system the pseudomonoclinic phase structure Bmm2 extending over the 0≤x ≤0.38 interval becomes pseudocubic at x≈ 0.2. The morphotropic region is spread over 0.38< × < 0.49; at higher PT concentrations (1.0 ≥ × ≥ 0.4…
Meltable Spin Transition Molecular Materials with Tunable Tc and Hysteresis Loop Width.
2015
Herein, we report a way to achieve abrupt high-spin to low-spin transition with controllable transition temperature and hysteresis width, relying not on solid-state cooperative interactions, but utilizing coherency between phase and spin transitions in neutral FeII meltable complexes
Probing the Thermochromic Phase Transition in CuMoO 4 by EXAFS Spectroscopy
2018
The work was supported by philanthropist MikroTik and administrated by the University of Latvia Foundation. The experiment at HASYLAB/DESY was performed within the project I-20160149 EC.
Spin crossover in metallomesogens
2009
Abstract In this review article are illustrated the strategies developed in order to achieve interplay/synergy between spin transition and liquid crystal transition. The synthesised Fe(II) metallomesogens exhibit different types of interplay between both phase transitions. A classification according to the analysis of the magnetic and structural data has led to the separation of three types of interplay, namely: type i systems with coupled phase transitions, subdivided into three groups a , b and c (in a the structural changes associated with the Cr ↔ LC drive the spin transition while in b these structural changes influence the spin state of the metallic centers but they are not the drivin…