The salt of the radical cation of 2,2'-bis-l,3-dithiole (TTF) and the radical anion of 7,7,8,8-tetracyanoquinodimethane (TCNQ), C18HaN4S4, crystallizes in the monoclinic system, space group P2~/c, with cell constants: a= 12.298 (6), b=3"819 (2), c= 18"468 (8) /~, fl= 104"46 (4) °, Z=2, Dm= 1"62 (1) and Dc=1"615 g cm -3. Intensities for 1373 independent reflections were collected on an automated diffractometer. The structure was solved by standard heavy-atom methods and has been refined by fullmatrix least-squares calculations to an R value of 0"044. The TTF radical cations and the TCNQ radical anions form homologous columnar stacks with interplanar spacings of 3.47 and 3.17 A, respectively. The dihedral angle between the least-squares planes of the cations and the anions is 58.5 ° and is approximately bisected by [010].

After hafnium carbide has been oxidized at temperatures in the range of 1400" to 2060°C, three distinct layers are present in the film cross section: (a) a residual carbide layer with dissolved oxygen in the lattice, (b) a dense-appearing oxide interlayer containing carbon, and (c) a porous outer layer of hafnium oxide. Experimental measurements of layer thicknesses and oxygen concentrations are combined with an extended formulation of moving-boundary diffusion theory to obtain the diffusion constants of oxygen in each of the three layers. The results indicate that the oxide interlayer is a better diffusion barrier for oxygen than either of the other layers. Based on X-ray microanalysis, X-ray diffraction, and resistance measurements, the interlayer is an oxygendeficient oxide of hafnium with a carbon impurity. The interlayer hardness equals that of the residual carbide layer.

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