In-Situ Synthesis, Crystal Structure and Properties of Yb2c2

Abstract

YB2C2 is a novel ultra-high temperature ceramic material with high damage tolerance. In this work, the in-situ synthesis mechanism, crystal structure, electronic structure, elastic properties and thermal shock resistance of YB2C2 was investigated systematically by experiment and calculations. From the X-ray diffraction, differential scanning calorimetry and thermodynamic calculations, it is revealed that YB2C2 is formed by the reaction of YB2C and C at above 1202 oC, and becomes the main phase at 1450 oC. In response to its controversy over the crystal structure, the space group of YB2C2 was determined to be P4/mbm by X-ray diffraction, transmission electron microscopy, Rietveld refinement and first-principles calculations, and the atom occupations are as follows: Y is located at 2a (0, 0, 0), B is located 4h (0.138, 0.638, 1/2) and C is located 4 h (0.0.6616, 0.1616, 1/2), respectively. The electronic structure, chemical bond and elastic properties of YB2C2 were calculated based on the determination of its crystal structure. The results show that the chemical bonding of YB2C2 displays sharp anisotropy, with strong B-C bond within the B2C2 nets, and weak Y-B/Y-C bond between Y atom layers and B2C2 nets. In addition, YB2C2 shows excellent thermal shock resistance with the residual flexural strength at up to 1300 oC being more than 70% of the strength at room temperature, which renders it a promising ultra-high temperature structural material.

Keywords: YB2C2, In-situ synthesis, Crystal structure, Properties