A comparative study of the influence of buoyancy driven fluid flow on GaAs crystal growth

A systematic investigation of the effect of gravity driven fluid flow on GaAs crystal growth was performed. It includes GaAs crystal growth in the microgravity environment aboard the Space Shuttle. The program involves a controlled comparative study of crystal growth under a variety of earth based conditions with variable orientation and applied magnetic field in addition to the microgravity growth. Earth based growth will be performed under stabilizing as well as destabilizing temperature gradients. The boules grown in space and on earth will be fully characterized to correlate the degree of convection with the distribution of impurities. Both macro- and micro-segregation will be determined. The space growth experiment will be flown in a self-contained payload container through NASA's Get Away Special program

Research for preparation of cation-conducting solids by high-pressure synthesis and other methods

It was shown that two body-centered-cubic skeleton structures, the Im3 KSbO3 phase and the defect-pyrochlore phase A(+)B2X6, do exhibit fast Na(+)-ion transport. The placement of anions at the tunnel intersection sites does not impede Na(+)-ion transport in (NaSb)3)(1/6 NaF), and may not in (Na(1+2x)Ta2 5F)(Ox). The activation energies are higher than those found in beta-alumina. There are two possible explanations for the higher activation energy: breathing of the bottleneck (site face or edge) through which the A(+) ions must pass on jumping from one site to another may be easier in a layer structure and/or A(+)-O bonding may be stronger in the cubic structures because the O(2-) ion bonds with two (instead of three) cations of the skeleton. If the former explanation is dominant, a lower activation energy may be achieved by optimizing the lattice parameter. If the latter is dominant, a new structural principle may have to be explored

Metamagnetism and critical fluctuations in high quality single crystals of the bilayer ruthenate Sr3Ru2O7

We report the results of low temperature transport, specific heat and magnetisation measurements on high quality single crystals of the bilayer perovskite Sr3Ru2O7, which is a close relative of the unconventional superconductor Sr2RuO4. Metamagnetism is observed, and transport and thermodynamic evidence for associated critical fluctuations is presented. These relatively unusual fluctuations might be pictured as variations in the Fermi surface topography itself. No equivalent behaviour has been observed in the metallic state of Sr2RuO4.Comment: 4 pages, 4 figures, Revtex 3.

EFFECTS OF HYDROSTATIC PRESSURE AND OF JAHN-TELLER DISTORTIONS ON THE MAGNETIC PROPERTIES OF RbFeF3

Nous avons déterminé dans RbFeF3 les rapports (ƊTi/ƊHa)p = 0,35 et 0,19°/kOe (ƊTi/ƊP)H = 0,18 et - 0,8l°/kbar pour les transitions de premier ordre à T1 = 40 °K et T2 = 87 °K. Les chaleurs latentes correspondantes sont 0,006 et 0,04 cal/g ; les variations des volumes relatifs sont ƊVi/Vi = 1,5 x 10-6 et - 22 x 10-6. Nous expliquons l'inhomogénéité de la température de Néel, les structures crystallographiques, le ferromagnétisme faible au-dessous de T2, ainsi que l'anisotropie magnétique cubique mesurée pour des champs supérieurs à 0,5 kOe.RbFeF3 exhibits first-order transitions at T1 = 40 °K and T2 = 87 °K. We report (ƊTi/ƊHa)p= 0.35 and 0.19 °/kOe, (ƊTi/ƊP)H = 0.18 and - 0.81°/kbar for T1 and T2, respectively, corresponding to latent heats 0.006 and 0.04 cal/g and relative volume changes ƊVi/ Vi = 1.5 x 10-6 and - 22 x 10-6. The inhomogeneity of the Néel temperature, the crystallographic structures, the weak ferromagnetism below T2, and the cubic magnetic anisotropy in an Ha > 0.5 kOe are interpreted