Microwave dielectric properties and crystal structures of 0.7CaTiO3–0.3[LaxNd(1−x)]AlO3 ceramics

• CTNA substituted 50% by La3+ exhibited good microwave dielectric properties.
• The structure of CTLNA changes from tetragonal to orthorhombic when x ⩾ 0.5.
• Intermediate phases disappear when the calcining temperature is higher than 1350 °C.
• 1% SrTiO3 added in CTLNA can reduce the porosity and improve the densification.

The microwave dielectric and sintering properties of 0.7CaTiO3–0.3[LaxNd(1−x)]AlO3 (CTLNA) specimens have been investigated in this work. It has been found that microwave dielectric properties and crystal structures depend on the LaAlO3 content. When x < 0.5, the crystal structure of 0.7CaTiO3–0.3[LaxNd(1−x)]AlO3 was tetragonal and it changed to the orthorhombic structure when x ⩾ 0.5. When x = 0.5, specimens exhibited excellent microwave dielectric properties with εr = 46.51, Q × f = 39,928 GHz (@3.8 GHz), τf = + 10 ppm/°C. In order to further improve the microwave dielectric properties of the samples, Ca2+ in 0.7CaTiO3–0.3[LaxNd(1−x)]AlO3 were partially substituted by Sr2+. The results showed that the addition of SrTiO3 inhibited the growth of the crystal grain and improved the densification of specimens. By optimizing the composition and preparation process, CTLNA specimens with δ = 0.01 in 0.7[SrδCa(1−δ)]TiO3–0.3[La0.5Nd0.5]AlO3 (SCTLNA) showed high density and a uniform grain structure with εr = 45.87, Q × f = 41612 GHz (@4 GHz), τf = + 10 ppm/°C.