Solid state phase equilibria in the ternary Nd–Si–B system at 1270 K

The solid state phase equilibria in the ternary Nd–Si–B diagram were determined at 1270 K using experimental techniques such as X-ray diffraction, scanning electron microscopy and electron probe microanalysis. No ternary compounds were obtained in the phase diagram with the exception of the interstitial Nowotny phase Nd5Si3Bx. The characteristic feature of this diagram is the major role played by the neodymium tetraboride NdB4, which is in thermodynamic equilibrium with all the binary silicides. The binary systems Nd–Si and Nd–B were re-investigated prior to the study of the ternary one. X-ray single crystal structures of Nd2B5 (Pr2B5-type), NdB4 (ThB4-type), Nd5Si3 (Cr5B3-type) and Nd5Si4 (in both types Zr5Si4 and Sm5Ge4) were solved. For the first time, Nd5Si4 has been found to adopt the Sm5Ge4-type. Structural relationships between NdB4, Nd2B5 and Gd2B5 on one side and between both forms of Nd5Si4 on the other side are largely discussed.