Lightweight (Ca,Mg)Zr₄(PO₄)₆(CMZP) ceramics have been fabricated with relative densities (P_lightweight/p_dense) of less than 0.35 by the polymer foam technique, and higher than 0.35 by the polymer powder technique. The polymer powder method forms an inhomogeneous pore structure having average pore sizes of 30-80 μm compared with the polymer foam method, which yields a large and uniform pore structures with pores 250-300 μm in diameter. The thermal expansion of the lightweight CMZP ceramics varies from positive (+2.7x1 0⁻⁶/â C) to negative (-2.6x10⁻⁶/ â C) with increasing grain size. The lightweight CMZP ceramics exhibit an excellent thermal shock resistance and this resistance is improved by increasing porosity. Mechanical properties including tensile strength, compressive strength, Modulus of rupture (MOR), and Young's moduli have been determined and vary exponentially with porosity. The strengths of the lightweight CMZP ceramics are superior to those of lightweight Zr0₂ with the same bulk density. Young's moduli, which were determined using a sonic velocity technique, range from about 5 GPa to 30 GPa, depending on the composition and the relative density. Furthermore, corrosion studies show that lightweight CMZP ceramics possess high resistance to acid corrosion at ambient temperature. / Master of Science