The dental zirconia–leucite composites were synthesized by high temperature solid-state method using potash feldspar, potassium carbonate and zirconia as raw materials. The mechanical properties and the coefficient of thermal expansion (CTE) of the prepared zirconia–leucite composites were tested. The results show that the bending strength, the fracture toughness and the metal–ceramic bonding strength of the prepared samples are about 110 MPa, 3.5 MPa/m^1/2 and 45 MPa, respectively. The CTE was about 13.73×10$^{-6}\ ^\circ $C^-1 and close to that of Ni–Cr dental alloy (14.0×10$^{-6}\ ^\circ $C^-1). The results indicate that the introduction of zirconia is beneficial to the improvement in the mechanical properties and CTE adjustment of porcelain material. The clinical application of the zirconia–leucite composites with good metal–ceramic bonding strength in the dental restoration could be envisioned.

A series of deuterated potassium dihydrogen phosphate (DKDP) crystals with different degrees of deuteration are grown from aqueous solution by the point-seed technique. The microhardness of (100), (001) and so-called ‘tripler’ faces for these DKDP crystals were measured. Initially the hardness number of (001) face for each crystal increases with the increase of the applied load until it reaches 25 g. With further increase in load, the hardness number decreases gradually. The hardness numbers decline with the increase in deuterium content. These composition dependences are expected since the bond strength is weakened by the substitution of deuterium for hydrogen. The hydrogen bond is considered to play the key role in effecting the crystal’s hardness. The visible hardness anisotropy of the different faces is attributed to the inhomogeneous distribution of the oxygen–hydrogen bond on these faces.