Crystal growth and negative thermal expansion properties of a Y2Mo4O15 single crystal

Abstract

A bulk-size single crystal of Y₂Mo₄O₁₅ with 20 × 11 × 8 mm³ was successfully grown by the top-seed solution growth (TSSG) method. The full-width at half maximum of (100) and (010) crystal faces is 37 and 27 arcsec, respectively. The thermal conductivity coefficients κ₁₁, κ₂₂, κ₃₃, and κ₁₃ are determined to be 1.519, 2.097, 0.445, and 0.997 W m⁻¹ K⁻¹, respectively. It is worth noting that the Y₂Mo₄O₁₅ crystal shows significant anisotropy thermal expansion properties, which exhibits a negative thermal expansion along the b-axis (α₂₂ = −5.11 × 10⁻⁶ K⁻¹). The crystal structure analysis shows that the shrinking of Mo–O bond lengths along the b-axis with the increasing temperature would be the main origin of the negative thermal expansion properties for Y₂Mo₄O₁₅ crystal, which does not comply with the current mechanism.