Pyrolysis of different polysilazanes has been used to prepare novel covalent amorphous ceramics composed of silicon, carbon, and nitrogen. The formation and structure of the as‐pyrolyzed amorphous state and its devitrification into stable crystalline phases have been investigated by means of nuclear magnetic resonance spectroscopy, infrared spectroscopy, thermogravimetry, mass spectroscopy, X‐ray and neutron diffraction, and by transmission electron microscopy. Additionally, the electrical conductivity and the compression creep behaviour of the as‐received materials have been analyzed.

Silicate glasses of the composition (Li2O)x(SiO2)100−x (x= 0, 20, 33.3, and 40) have been prepared and characterized by X‐ray and neutron diffraction experiments using the technique of isotopic substitution. Thus, at each composition, a set of independent diffraction patterns allows the discussion of the short‐range and medium‐range structure. For the short‐range structure, average coordination numbers and atomic‐pair distances are obtained from the pairdistribution functions. For the medium‐range structure, i.e., for atomic‐pair distances >0.5 nm, an increase of the amplitudes of the oscillations in the pair‐distribution function is observed with increases in the Li2O content.

The results of X‐ray and neutron diffraction experiments with (Li2O)x(SiO2)100_x glasses (x = 0, 20, 33.3, and 40) are discussed using the Reverse Monte Carlo method to produce atomic clusters, which are analyzed with respect to the O‐O distribution, the angular correlations within the first and higher coordination spheres, and the bond‐orientational multipole moments. Within Li2O‐containing silicate glasses, each lithium atom is surrounded by a ring of six SiO4 tetrahedra in such a way that four oxygen atoms lie at the joints of a tetragonal cell centered by lithium. Thus, the lithium atoms increase the order of the glass.

In the present work, amorphous Si

Short-Range and Medium-Range Order in Lithium Silicate Glasses. Part 1. Diffraction Experiments and Results.-Neutron and X-ray diffraction experiments including isotopic substitution methods enable the description of both short-and medium-range structures of glasses of the composition (Li2O)x(SiO2)100-x (X: 0, 20, 33.3, 40). Atomic pair distances and partial coordination numbers obtained from the pair distribution functions are presented for the short-range structure. In the medium-range region, i.e. for distances ¿ 0.5 nm, the amplitudes of oscillation in the pair-distribution junction increase with increasing Li2O content. -(UHLIG, H.; HOFFMANN, M. J.; LAMPARTER, H.-P.; ALDINGER, F.; BELLISSENT, R.; STEEB, S.; J.