Bi 0.33 Zr 2 (PO 4 ) 3 , a negative thermal expansion material with a Nasicon-type structure.

A new negative thermal expansion ceramic material, Bi 0.33 Zr 2 (PO 4 ) 3 , with a sodium zirconium phosphate structure, has been investigated and the results are presented. A three-dimensional structural framework is formed by the interconnection of ZrO 6 octahedra and PO 4 tetrahedra through their vertices. The occupation of a Bi ion in a type I site, located between two ZrO 6 octahedra along ZrO 6 < PO 4 > ZrO 6 ribbons induced the structure to crystallize in a trigonal system with a P 3̄ c 1 space group. The average thermal expansion coefficients between 300 and 1073 K are found to be α a = -12.99 × 10 -6 K -1 , α c = -26.67 × 10 -6 K -1 , and α v = -52.25 × 10 -6 K -1 . The large negative thermal expansion is highly associated with the peak shift towards a higher angle in temperature variable X-ray diffraction patterns, coupled rotation and distortion of ZrO 6 octahedra and PO 4 tetrahedra, and elongation or shrinkage in the Zr-O-P bond angles. Dilatometer results authenticate the negative thermal expansion behavior. The average bulk thermal expansion is registered as -0.73 × 10 -6 K -1 .