Abstract
High-density xCaTiO3–(1−x)La(Mg1∕2Ti1∕2)O3 ceramics (x=0.0–1.0) were prepared by solid-state reaction. The products were characterized by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. CaTiO3–La(Mg1∕2Ti1∕2)O3 ceramics formed solid solutions throughout the compositional range with no evidence of a secondary phase. For most ceramics the symmetry was orthorhombic with Pbnm space group. The La(Mg1∕2Ti1∕2)O3 end member exhibited 1:1 ordering of Mg2+ and Ti4+ cations (in octahedral sites) superimposed on the perovskite distortions leading to monoclinic symmetry with P21∕n space group. Long-range 1:1 order of Mg2+ and Ti4+ cations was destroyed at x=0.3. The degree of distortion, unit-cell volume, and crystal lattice stress decreased with increasing CaTiO3 content. Twin and antiphase domains, generated by structural phase transitions on cooling, were observed in all the ceramics. Twin domain density increased with CaTiO3 content but the size of individual domains decreased. The twin domains were classified according to the symmetry elements at the twin boundaries as {112} and (110) twin types. The microwave dielectric properties (at 3.5–5.5 GHz) showed a strong dependence on composition. The relative permittivity (εr) and temperature coefficient of resonant frequency (TCf) increased nonlinearly with CaTiO3 content (εr29–170; TCf −50 to +710 ppm∕°C). In contrast Qf (GHz) values decreased approximately linearly with CaTiO3 content (48 000–5790). Near zero TCf (1.06 ppm∕°C) was attained at x=0.55, where εr=44.6 and Qf=32000GHz. The increase in relative permittivity and TCf with CaTiO3 content correlated with the reduction in composition-induced lattice stress in association with increasing macroscopic polarizability.
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call