No abstract

Structural investigations of the compounds in the series Ba0.27Sr0.73ZryTi1-yO3 have been carried out. The crystal structure goes to lower symmetry with increasing Zr content and the tolerance factor decreases. The variation of Va/Vb is linear with the tolerance factor. The tilt system is a-a-c0 for compositions with y = 0.50 and 0.65. The tilt system is a-a-c+ for compositions with y = 0.80, 0.90 and 0.97 and for BSZT (Ba0.29Sr0.71Zr0.97Ti0.03O3) and BSZTTa (Ba0.29Sr0.71Zr0.95Ti0.04Ta0.01O3). The tilt angle with respect to the pseudocubic [100] and [001] directions increases with the Zr content. For compositions with y = 0, 0.25 and 0.40, the coordination of the A ion (Ba or Sr) is 12, whereas the A-ion coordination number is 11 for compounds with y = 0.50 and 0.65 and it is lower for compositions with y = 0.80, 0.90 and 0.97 and for the compounds BSZT and BSZTTa. The decrease in coordination number indicates that the compounds are becoming more and more covalent with increasing Zr content. A graph of |90°-pc| against the tolerance factor shows that |90°-pc| falls sharply at a tolerance factor corresponding to the compositions used in the fabrication of dielectric resonators. TCf values show that the sign of this parameter changes at a tolerance factor near 0.965 and has a minimum for compounds with orthorhombic Pbnm/Pnma structures.

Abstract. The simple direct method for solving projections of centrosymmetric crystals [Swaminathan & Lessinger, Cryst. (1973), A29, 717-720; A30, 458] has been found quite effective for the centrosymmetric projections of two non-centrosymmetric crystals: (i) the unique axis projection of chlorooxoishwarone (P2~)and (ii)the c-axis projection of 2,6-dimethoxybenzoic acid (P212t20. more than one contradiction or those of alternative possibilities are to be avoided as suspect. Coincidences (Table 3) resulting from the ~2 relations give on feedback the sign of the reflexion 602, code No. 50, to be positive. The three consistent indications in Table 3 are further reinforced by a ~ indication, S(47) S (47) s(50) = + 1.

We conduct a series of numerical experiments into the nature of three-dimensional (3D) hydrodynamics in the postbounce stalled-shock phase of core-collapse supernovae using 3D general-relativistic hydrodynamic simulations of a 27 M e progenitor star with a neutrino leakage/heating scheme. We vary the strength of neutrino heating and find three cases of 3D dynamics: (1) neutrino-driven convection, (2) initially neutrino-driven convection and subsequent development of the standing accretion shock instability (SASI), and (3) SASIdominated evolution. This confirms previous 3D results of Hanke et al. and Couch & Connor. We carry out simulations with resolutions differing by up to a factor of ∼4 and demonstrate that low resolution is artificially favorable for explosion in the 3D convection-dominated case since it decreases the efficiency of energy transport to small scales. Low resolution results in higher radial convective fluxes of energy and enthalpy, more fully buoyant mass, and stronger neutrino heating. In the SASI-dominated case, lower resolution damps SASI oscillations. In the convection-dominated case, a quasi-stationary angular kinetic energy spectrum E(ℓ) develops in the heating layer. Like other 3D studies, we find E(ℓ) ∝ℓ −1 in the "inertial range," while theory and local simulations argue for E(ℓ) ∝ ℓ −5/3 . We argue that current 3D simulations do not resolve the inertial range of turbulence and are affected by numerical viscosity up to the energy-containing scale, creating a "bottleneck" that prevents an efficient turbulent cascade.

Structural study on the compound Ca0.6Sr0.4ZrO3 has been carried out. The study reveals that it is not isomorphous with its parent compounds CaZrO3 and SrZrO3. It belongs to the space group Pmcn and the size of the unit cell is 2a p×√ 2b p×2√ 2c p. The tilt system of the BO6 octahedra is found to be compound and the octahedra are highly distorted. The A-ions are displaced along the [001] direction by about 0.134 Å and the displacements in adjacent layers are in the opposite directions.