Systematic and controllable negative, zero, and positive thermal expansion in cubic Zr_1-xSn_xMo₂O₈

We describe the synthesis and characterization of a family of materials, Zr_1-xSn_xMo₂O₈ (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, α_l, ranging from -7.9(2) × 10^-6 to +5.9(2) × 10^-6 K^-1 (12-500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of "cubic" SnMo₂O ₈, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material.