Crystal structures, dielectric properties, and lattice vibrational characteristics of (1-x)CaWO4-xTiO2 composite ceramics

Lattice vibrational characteristics, crystal structures and dielectric properties of non-stoichiometric Nd(1+x)(Mg1/2Sn1/2)O3 ceramics

A CaMgGeO4 (CMG) ceramic with an olivine structure was fabricated by the traditional solid-phase reaction method; this material was dense at 1300 °C/6 h and exhibited excellent dielectric properties (er = 6.83, Q × f = 125 432, f = 14.9 GHz). The effects of BaCu(B2O5) (BCB) on the sintering characteristics, crystal structures and microwave dielectric properties of CMG systems were studied. BCB can effectively reduce the sintering temperature (Ts) of the CMG ceramic, and when the amount of BCB is 16 wt%, the Ts can be lowered to 875 °C. The CMG ceramic containing 8 wt% BCB shows excellent dielectric properties (er = 7.01, Q × f = 73 962, f = 14.8 GHz) at 940 °C/6 h. Raman mode 11 moves to a lower wavenumber with increasing BCB content, while the BCB content has the opposite effect on the dielectric constant; however, the full width at half-maximum (FWHM) value of mode 11 correlates negatively with the Q × f values. In addition, the change in the packing fraction is similar to that in the Q × f values with increasing BCB content. A decrease in the packing fraction means an increase in the vibrational space and possibly non-resonance, which in turn reduces the Q × f value. In addition, the ceramic has good chemical compatibility with the Ag electrode, indicating broad application prospects in low-temperature co-fired ceramics (LTCCs) for CMG.

Effects of BaCu(B2O5) additives on the crystal structures and dielectric properties of CaMgGeO4 ceramics for LTCC applications

New Directions In Solid State Chemistry

Crystal structures and microwave dielectric properties of Sr2MgWO6 ceramics at different sintering temperatures

Complex perovskite microwave dielectric ceramics (MWDCs) of A ( B 1 / 3 ′ B 2 / 3 ′ ′ ) O 3 -type (A = Ba, Sr,…; B′ = Mg, Zn,…; B″ = Nb, Ta), which exhibit excellent dielectric properties, have currently been widely used in microwave and millimetre wave devices. Vibrational spectra, including both Raman and far-infrared (FIR) spectra, are powerful tools to investigate the atomic thermal vibrational properties of MWDCs and reveal the intrinsic origin of dielectric properties. In this review, lattice dynamics and phonon characteristics of the A ( B 1 / 3 ′ B 2 / 3 ′ ′ ) O 3 -type MWDCs are summarised and presented in detail to introduce remarkable progress in this field and make a guide for the design of novel advanced MWDCs. The atomic sites and the corresponding modes in Raman and FIR spectra are identified and illuminated. The effects of the processing conditions and the ordered superstructures in the nanoscale region on vibrational modes are summarised systemically. Intrinsic properties can be extrapolated from the fitting results of FIR spectroscopy, which were also discussed based on the Kramers–Kronig relations, Lorentz three-parameter classical model and four-parameter semi-quantum model. The correlations between vibrational modes (phonons), crystal structures, and dielectric properties are created, which can help to build the mathematical models so as to understand the structure–property relationship of MWDCs better.

Chun-Hai Wang

Papers

Lattice dynamics and phonon characteristics of complex perovskite microwave ceramics