To examine the origin of negative thermal expansion in oxides ZrV x P 2-x O 7 (x=0-2) andAW 2 O 8 (A=Zr, Hf),ab initioself-consistent-field molecular orbital calculations were carried out for a model compound (HO) 3 P-O-P(OH) 2+ 3 . Our study suggests that symmetric stretching vibrations of two-coordinate oxygen bridges are strongly coupled with their bending vibrations and are more important for negative thermal expansion at high temperature. The oxygen bridges accomodate a large stretching of theA-O (A=Zr, Hf) andM-O (M=P,V) bonds at high temperature by decreasing the bond angles of the oxygen bridges. When the bond angles increase, the bonds are shortened due to the π-type orbital interactions associated with the oxygen lone pair orbitals.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry