Thermal expansion of spinel-type ${\mathrm{Si}}_3{\mathrm{N}}_4$

The lattice parameter and thermal expansion coefficient (TEC) for the spinel-type ${\mathrm{Si}}_3{\mathrm{N}}_4$ phase prepared under high-pressure and high-temperature conditions are determined for $14\mathrm{K}<T<\mathrm{}302\mathrm{}\mathrm{K}$ by x-ray diffraction, at a synchrotron-radiation source, and for $0\mathrm{K}<T<\mathrm{}1683\mathrm{}\mathrm{K}$ by first-principles calculations. The low- and high-temperature experimental TEC data are in excellent agreement with the calculations. Our results provide the first experimental evidence that the linear expansion coefficient tends to vanish for $T<\mathrm{}100\mathrm{}\mathrm{K}.$ The experimental temperature dependence of the TEC is accurately represented by polynomials over the complete $T$ range.