Nam-Kyoung Kim

Perovskite formation sequence by B-site precursor method and dielectric properties of PFW-PFN ceramics

Abstract The reaction sequences of B-site precursors and perovskite phase formation, crystallographic data, dielectric properties, and microstructures in the PFW-PFN system are reported. The formations of B-site precursors and perovskite phases were studied by X-ray diffraction. B-site precursors formed directly from the constituent oxides or through a competition with a pyrochlore-type structure, while perovskite phases were developed through a competition with pyrochlores. Maximum dielectric constants and Curie temperatures (@100 kHz) of PFW and PFN were found as 8,400 and 23,000 at −71° and 110°C, respectively. PFW exhibited a typical relaxor behavior, whereas PFN showed little relaxation.

Phase developments and dielectric/ferroelectric responses in the PMN–PT system

Abstract Monophasic (⩾99.4%) perovskite powders of a Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 system were prepared by a B-site precursor method. Phase developments and lattice parameter changes in the perovskite system were examined by X-ray diffraction. Weak-field dielectric responses of the ceramic system were investigated as functions of PbTiO 3 concentration and measurement frequency. Phase transition modes in the dielectric spectra were analyzed in terms of diffuseness characteristics. Ferroelectric hysteresis behaviors were monitored with respect to temperature changes.

Preparation and dielectric properties of Pb[(Mg1/3Ta2/3), (Zn1/3Nb2/3)]O3 relaxor ceramics

Abstract Powders of Pb(Mg1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 ceramic system were prepared by a B-site precursor method. Perovskite phase contents and lattice parameters of the system are reported. Weak-field radio-frequency dielectric constants and losses of sintered samples were investigated as functions of composition, temperature, and frequency. Dielectric relaxation and diffuse phase transition behaviors were characterized. Microstructures were examined and correlated with dielectric characteristics.

Stabilization of perovskite phase and enhancement in dielectric properties by substitution of Pb(Mg1/3Nb2/3)O3 to Pb(Zn1/3Ta2/3)O3

Abstract Stabilization of a perovskite structure in the Pb(Zn1/3Ta2/3)O3-Pb(Mg1/3Nb2/3)O3 system was attempted. System powders were prepared by reacting PbO and pre-synthesized B-site precursor compositions. Perovskite phase developments were studied as functions of substituent amounts and heat-treatment stages. Formation tendencies of perovskite/pyrochlore structures were discussed in terms of electronegativity difference and tolerance factor. Dielectric properties of the system ceramics were investigated, with further analyses on diffuseness characteristics in the dielectric constant spectra.

Perovskite phase developments in Pb[(Mg,Zn)1/3Ta2/3]O3 system and dielectric characteristics

Stabilization of a perovskite structure was attempted by replacing Mg for Zn in Pb(Zn1/3Ta2/3)O3. System powders were prepared using a B-site precursor method by reacting PbO with separately-prepared precursor compositions. Effects of the substituent Mg concentration on perovskite phase developments and subsequent changes in dielectric properties were investigated, as a function of measurement frequency. Phase transition modes reflected in the dielectric constant spectra were analyzed in terms of diffuseness exponent and degree of diffuseness. Internal microstructures of the ceramics were examined, and correlations with perovskite phase contents and dielectric properties are discussed.

Crystallographic, dielectric, and diffuseness characteristics of PZN–PT ceramics

Abstract Nearly-monophasic powders of Pb(Zn 1/3 Nb 2/3 )O 3 –PbTiO 3 (PZN–PT) with perovskite structure were prepared (except for PZN) by the B-site precursor method and densified into ceramic form. Phase transition modes between second-order relaxor-type and first-order normal-ferroelectric-type were studied in terms of phase developments, crystallographic aspects, dielectric constants, and diffuseness characteristics of dielectric constant spectra.

Lead magnesium tantalate-lead titanate perovskite ceramic system : preparation and characterization

Abstract Selected composition ceramics in the Pb(Mg 1/3 Ta 2/3 )O 3 –PbTiO 3 system were prepared and characterized. Phases developed in the B-site precursor and perovskite systems were examined by X-ray diffraction. Dependencies of the lattice constants and dielectric properties upon composition were investigated. Dielectric relaxation modes in the paraelectric temperature range were quantitatively analyzed in terms of diffuseness parameters. Ferroelectric hysteresis responses with changes in temperature were monitored. Dielectric maximum temperatures in the system increased steadily with increasing PbTiO 3 concentration, whereas maximum dielectric constants were higher at intermediate compositions.

Perovskite phase developments and dielectric characteristics in barium-substituted lead zinc tantalate system

Abstract Phase formations in Pb(Zn1/3Ta2/3)O3, with Ba partially/fully substituted for Pb as a perovskite stabilizer, were studied. Ceramic powders were prepared by a B-site precursor method in order to enhance the perovskite yields. Lattice parameters of the pyrochlore and perovskite structures were determined. Weak-field low-frequency dielectric properties of the ceramics were measured, and diffuseness characteristics reflected in the dielectric spectra were evaluated. Microstructures of the fracture surfaces were examined.

Synthesis chemistry of MgNb2O6 and Pb(Mg1/3Nb2/3) O3

The sequences of chemical and structural changes accompanying the syntheses of colurnbite MgNb2O6 (from MgO and Nb2O5) and perovskite Pb(Mg1/3Nb2/3)O3 (from PbO and MgNb2O6) were investigated. MgNb2O6 formed completely after first competing with the formation of an intermediate pyrochlore phase. Pb(Mg1/3Nb2/3)O3 first formed completely from PbO and MgNb2O6, then decomposed into pyrochlore, which decomposed again into the precursors MgNb2O6 and PbO.

Preparation of Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 ceramics by the B-site precursor method and dielectric characteristics

Powders in the Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 system, with a high perovskite yield, were prepared by a B-site precursor method. PbO was added to pre-reacted B-site components of Mg1-xZnxNb2O6 solid solution, which was further calcined to form a perovskite structure. Perovskite phase contents and lattice parameters were obtained from X-ray analyses. Weak-field low-frequency dielectric constants and losses of sintered pellets were measured as functions of composition, temperature and frequency. Dielectric relaxation behaviours were investigated in terms of diffuseness coefficients. Microstructures were observed to correlate with other characteristics.