Normal zirconium phosphate, ZrP₂O₇, has a reversible inversion at 300 degrees C and at 1,550 degrees C dissociates into zirconyl phosphate, (ZrO)₂P₂O₇, with loss of P₂O₅as vapor. Zirconyl phosphate is stable up to about 1,600 degrees C and has a very low thermal expansion--1 x 10_-6(20 to 1,000 degrees C).