Structure and thermal motion parameters of tetragonal ZnP2 between 300 and 740 K

Abstract

The lattice constants and thermal motion parameters of tetragonal ZnP2 are measured between 300 and 740 K using X‐ray diffraction on single crystals. Absolute measurements of integrated intensities show that the crystals are nearly perfect. At 300 K the lattice constants are a = (5.07250 ± 0.00003) Å and c = (18.5529 ± 0.0001) Å. The coefficients of linear expansion are αa = 6.50 × 10−6 K−1, αc = 6.25 × 10−6 K−1 below 380 K and αa = 7.90 × 10−6 K−1, αc = 6.95 × 10−6 K−1 above this temperature. Between 377 and 382 K there is a region of hysteresis where Δc = 0.0003 Å. The crystal structure stays tetragonal at least up to 740 K, and the lattice instability near 380 K is suggested to arise from excitation of a soft mode. The average thermal motion parameters at 300 K are B [00.1] = (0.95 × 0.1) Å2 (perpendicular to the basal plane) and B = [11.0] = (0.7 × 0.1) Å2 (in the basal plane). The increase with temperature is linear; ΔB [00.1]/ΔT = 3 × 10−3 xA2 K−1, ΔB [11.0]/ΔT = 2.5 × 10−3 Å2 K−1; up to T = 550 K, where the effects of anharmonicity become noticeable.