The synthesis of elementoorganic polymers and their subsequenttransformation into inorganic materials by thermolysis is a novel approachto design new materials providing semiconducting properties and high oxidationresistance at high temperatures. Amorphous B28C40N32ceramics were produced by thermolysis of a polyborcarbodiimide precursorat 1100C in argon gas atmosphere.X-ray wide angle scattering shows that the samples are fully amorphousup to 1600C. In order to investigatethe medium range structure of the amorphous ceramics, small angle scatteringexperiments were performed. For the identification of the scattering centresthe methode of contrast variation was employed. This was achieved by combinationof small angle X-ray scattering (SAXS) experiments with small angle neutronscattering (SANS) measurements. In order to suppress the influence of surfacescattering the immersion technique with suitable mixtures of C2H5OHand C2D5OD was applied. These experiments revealed,that the amorphous ceramics contain heterogeneities in the order of 20caused by phase separation in the amorphous matrix. Further on, the temperaturedependence of the medium range structure of the samples was investigated.A strong temperature-time dependence is determined considering the Guinierradius of the scattering regions of the annealed samples. Investigationsof the crystallisation process during heat treatment up to 2000Csuggest the formation of a carbon rich ternary boroncarbonitride phase.
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