Bi0.33Zr2(PO4)3, a Negative Thermal Expansion Material with a Nasicon-type Structure

A new negative thermal expansion ceramic material, Bi0.33Zr2(PO4)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 ZrO6 octahedra and PO4 tetrahedra through their vertices. The occupation of a Bi ion in a type I site, located between two ZrO6 octahedra along ZrO6 < PO4 > ZrO6 ribbons induced the structure to crystallize in a trigonal system with a P3̄c1 space group. The average thermal expansion coefficients between 300 and 1073 K are found to be αa = -12.99 × 10-6 K-1, αc = -26.67 × 10-6 K-1, and αv = -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 ZrO6 octahedra and PO4 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.