Features of measuring the temperature dependences of the electric resistance of carbon materials obtained by thermolysis of mixtures of phenolphthalein with melamine

Carbon materials with high nitrogen content show great potential for modern electronics. To obtain such materials, it is convenient to use melamine as a source of nitrogen, since during its thermal decomposition a significant amount of nitrogen-containing groups is formed, which can be incorporated into the structure of the carbon material. The study of the temperature dependence of resistance for the obtained materials has made it possible to establish the effect of nitrogen atoms on the band structure of the samples. The article describes a method for obtaining single-phase nitrogen-containing solid solutions, based on amorphous carbon, by thermolysis of molten mixtures of melamine with phenolphthalein under heating to 500 °C. This method has made it possible to achieve the nitrogen content of 21 wt. %. The results of the study of new materials by the X-ray phase analysis are presented, confirming the chaotic structure of solid solutions and the absence of long-range order in the arrangement of carbon or nitrogen atoms. The morphology of the obtained samples with various concentrations of phenolphthalein varies from loosely bound powders to solid foam. The complexity of measuring the temperature dependences of resistivity is associated with the difficulty of preparing standard rectangular samples. To measure the temperature dependences of resistance, the samples were ground to a powder of the given granulometric composition, and a vacuum measuring cell was constructed, as well as measurement technique was developed in the range of 30-300 °C. The paper describes the experimental setup and sample preparation, and also presents the results of measurements of samples of solid solutions of nitrogen in amorphous carbon with a high nitrogen content. A monotonical decrease in the band gap of solid solutions from 1.07 to 0.61 eV with an increase in the nitrogen content in them has been shown.