Antiferroelectricity-Induced Negative Thermal Expansion in Double Perovskite Pb 2 CoMoO 6 .

Materials with negative thermal expansion (NTE) attract significant research attention owing to their unique physical properties and promising applications. Although ferroelectric phase transitions leading to NTE are widely investigated, information on antiferroelectricity-induced NTE remains limited. In this study, single-crystal and polycrystalline Pb 2 CoMoO 6 samples are prepared at high pressure and temperature conditions. The compound crystallizes into an antiferroelectric Pnma orthorhombic double perovskite structure at room temperature owing to the opposite displacements dominated by Pb 2+ ions. With increasing temperature to 400 K, a structural phase transition to cubic Fm-3m paraelectric phase occurs, accompanied by a sharp volume contraction of 0.41%. This is the first report of an antiferroelectric-to-paraelectric transition-induced NTE in Pb 2 CoMoO 6 . Moreover, the compound also exhibits remarkable NTE with an average volumetric coefficient of thermal expansion α V = -1.33 × 10 -5 K -1 in a wide temperature range of 30-420 K. The as-prepared Pb 2 CoMoO 6 thus serves as a prototype material system for studying antiferroelectricity-induced NTE.