Crystal growth and negative thermal expansion properties of a Y 2 Mo 4 O 15 single crystal.

A bulk-size single crystal of Y 2 Mo 4 O 15 with 20 × 11 × 8 mm 3 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 κ 11 , κ 22 , κ 33 , and κ 13 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 Y 2 Mo 4 O 15 crystal shows significant anisotropy thermal expansion properties, which exhibits a negative thermal expansion along the b -axis ( α 22 = -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 Y 2 Mo 4 O 15 crystal, which does not comply with the current mechanism.