A lattice constant of a. = 4.4555 =t 0.0003 A. has been determined for TaCo.ast * 0.00'1 at 25". The equation a 0 = 4.3007 + Solution of this equation for TaCl.oo 0.1563 (C/Ta) has been calculated relating composition to lattice parameter of TaC.gives a lattice parameter of 4.4570 =k 0.0010 A.
Tantalum carbide and niobium carbide samples with carbon-to-metal molar ratios varying from 0.754 to 0.987 for tantalum carbide and from 0.70 to 0.977 for niobium carbide were examined for superconductivity. Both niobium and tantalum carbides were found to be superconducting with transition temperatures which vary with composition. The major conclusion is that the highest temperature is reached for the stoichiometric composition and any deviation therefrom results in a lowering and eventual disappearance (less than 1.05°K) of T c .
Neutron diffraction studies of several of the D2O ice polymorphs were made with helium pressures to 3.5 kbar. Volume compressions (ΔV / V) were obtained for ices Ih, Ic, and IX at 2.1 to 2.8 kbar. The equilibrium phase boundaries between ices I–II and I–III in the presence of helium are shifted toward higher pressure values. The crystal structures of ices Ih, Ic, II, and IX at approximately 2.5 kbar are the same as the structures found for these ice forms at atmospheric pressure. A tetragonal structure is indicated for ice III with lattice parameters at − 23°C and 2.7 kbar of a = 6.674 ± 0.015 Å and c = 6.97 ± 0.03 Å. The c / a ratio for ice IX has been found to be 1.000 ± 0.003 both at 1 bar and at 2.8 kbar.
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