Synthesis and Thermal Expansion of MZr sub 4 P sub 6 O sub 24 (M = Magnesium, Calcium, Strontium, Barium)

MZr sub 4 P sub 6 O sub 24 (M = magnesium, Ca, Sr, Ba), which belongs to a new, low-thermal-expansion family of materials known as (NZP) or (CTP), were synthesized by solid-state reaction (oxide mixing) and sol--gel methods, and their sinterability in two cases was investigated and compared. Thermal-expansion measurements were made on sintered samples by dilatometry, high-temperature X-ray diffractometry, and the laser speckle technique. An anisotropy in axial thermal-expansion coefficients was observed in these materials. CaZr sub 4 P sub 6 O sub 24 and SrZr sub 4 P sub 6 O sub 24 showed reverse anisotropy and opposite bulk therml expansion, i.e. CaZr sub 4 P sub 6 O sub 24 had negative bulk thermal expansion and SrZr sub 4 P sub 6 O sub 24 positive bulk thermal expansion in the temperature range 25-500 deg C. The microstructure of the sintered samples was also examined by scanning electron microscopy. 15 ref.--AA