V. N. Molchanov

Structure of superconducting single crystals of 2201 thallium cuprate (Tl1.85Cu0.15)Ba2CuO6, Tc = 110 K

Abstract Single crystals of 2201 phase with various superconducting transition temperatures ranging from nonsuperconducting to 110K have been obtained. An X-ray structural study of tetragonal single crystals with Tc = 110 K, space group 14/mmm, a = 3.8686(3), c = 23.259(3) A, has been carreid out. We have found that thallium atoms are partially replaced by copper atoms. We have also found that Tl atoms and O(3) atoms linked with Tl are displaced from their symmetrical sites. A correlation between the structure and properties of Tl-2201 cuprate crystals has been established on the basis of our data and the data reported in the literature.

Crystal structure and optical activity of La3Nb0.5Ga5.5O14 and Sr3Ga2Ge4O14 single crystals of the langasite family

Precision X-ray structural studies of the La3Nb0.5Ga5.5O14 and Sr3Ga2Ge4O14 single crystals were carried out. The space group P321 was confirmed. The anomalous X-ray scattering was taken into account to establish the absolute structures (chirality) of the crystals; they proved to be of different sign. The structural features responsible for the optical activity of crystals were revealed, and the dependence of the magnitude and sign of specific rotation on the structural parameters of these compounds were determined.

Lattice parameters of La3Ga5SiO14 as a function of hydrostatic pressure

Abstract Langasite (La3Ga5SiO14) crystallizes in the polar space group P321. Here we report the pressure dependence of the lattice parameters at high hydrostatic pressures up to 10.2 GPa. The results presented in terms of compressibility agree well with results from measurements of the elastic constants. According to a Birch-Murnaghan equation of state, the bulk modulus and its pressure derivative are 134.6(2) and 2.8(1) GPa, respectively. The compression of langasite crystals is anisotropic, the c/a-ratio appears to be a linear function of the pressure applied according to c/a = 0.62460(6) + 0.00055(1)* p/GPa. Altogether four single crystals have been investigated. Two of them showed a splitting of reflections (hhl). This splitting reaches a maximum at approximately 9 GPa and proved to be reversible.

Comparative study of Tl-2201 single crystals with Tc = 30 and 110 K by means of X-ray structural analysis and NMR

Abstract The crystal structure of a tetragonal single crystal of Tl-2201 with Tc = 30 K has been determined by the X-ray diffraction technique (a = 3.8717(3), c = 23.224(3) A, space group I4/mmm, Z = 2). The chemical composition is found to be Tl1.90(1)Cu.0.10(1)Ba2CuO6.18(4). Displacements of Tl and O3 atoms from their symmetric sites have been observed. Structural parameters of Tl-2201 cuprates with various Tc have been compared. The superconducting transition temperature is shown to correlate most strongly with the parameter c, with the length of the bond between Cu and apical oxygen as well as with the distance between Ba2+ and the cuprate plane.

Enantiomorphism of the Ca3Ga2Ge4O14 compound and comparison of the Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 structures

The absolute crystal structures of two enantiomorphic forms of the Ca3Ga2Ge4O14 crystals (a = 8.075(1) Å, c = 4.9723(6) Å, space group P321) with the positive and negative senses of the optical activity are determined using X-ray diffraction analysis. The final R factors are as follows: R = 1.75% and Rw = 2.57% for the crystal with the positive sense of the optical activity and R = 1.86% and Rw = 2.78% for the crystal with the negative sense of the optical activity. The replacement of the Ca2+ ions by larger Sr2+ ions (with the formation of the Sr3Ga2Ge4O14 compound) leads to an anisotropic expansion of the crystal lattice (with a more considerable increase in the lattice parameter a as compared to the lattice parameter c), a change in the occupation of the 1a and 3f positions by the Ga3+ and Ge4+ ions, and symmetrization of the octahedra and tetrahedra forming the structural framework. The shape of the dodecahedron changes so that its size along the polar electric axis 2 increases significantly. This change is the main factor responsible for the increase in the piezoelectric activity of the Sr3Ga2Ge4O14 compound as compared to the piezoelectric activity of the Ca3Ga2Ge4O14 compound.

Crystal structure of the new barium borate Ba5(BO3)2(B2O5)

The crystal structure of the new barium borate Ba5(BO3)2(B2O5) is established (R = 0.0436). Single crystals were grown by spontaneous crystallization in the BaO-B2O3-Na2O system using the flux method. This compound crystallizes in the orthorhombic system, sp. gr. P212121; the unit-cell parameters are a = 9.590(2) Å, b = 16.659(3) Å, c = 22.919(6) Å, and Z = 12. The structure consists of coordination polyhedra of barium cations and the anionic groups [BO3] (planar triangles) and [B2O5] (vertex-sharing double [BO3] triangles), which form a pseudohexagonal framework. Melting of barium borate occurs by a peritectic reaction at 1170 ± 10°C.

Nanostructured crystals of the fluorite phases Sr1 − xRxF2 + x(R—rare-earth elements) and their ordering: II. Crystal structure of the ordered Sr4Lu3F17 phase

AbstractThe crystal structure of the ordered phase Sr4Lu3F17 prepared by directed crystallization of the melt has been investigated. The crystals have a trigonally distorted fluorite lattice (space group R % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC % vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz % ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb % L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe % pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam % aaeaqbaaGcbaGafG4mamJbaebaaaa!3BD7!

Growth and structure of barium sodium orthoborate NaBaBO3 crystals

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