Ultralow‐expansion Ceramics in the System Na 2 O‐zro 2 P 2 O 5 ‐sio 2

Compositions in the series Na 1+x Zr 2 P3‐ x Si x O 12 and Na 1+4z Zr 2 ‐ z P 3 O 12 , where x = 0≤x≤1 and z=0≤z≤1/2, have thermal expansions that can be controlled (by selecting the composition) to values in the range <10×10 ‐7 in a temperature regime of a few hundred degrees. The lowest a values were obtained for x ∼0.33 and z∼0.125.