Preparation and electrical properties of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> solid solutions

Ceramic samples of lead magnesium niobate (PMN) and (1 ? x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ (PMN-PT) solid solutions with x = 0, 0.05, 0.10, and 0.30 have been prepared by solid-state reactions, and their structural, electrical, and piezoelectric properties have been studied using x-ray diffraction, Rietveld profile analysis, impedance spectroscopy, and the resonance/antiresonance method. The results indicate that the use of nonstoichiometric columbite niobates enables the synthesis of phase-pure PMN and PMN-PT.     

Phase developments in Pb(Mg<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> and Pb(Zn<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> via B-site precursor route

Phase formation stages of MgWO₄ and ZnWO₄ (precursor compositions for following steps) were investigated by monitoring the reactions of oxide chemicals at various temperatures. Developed phases were examined by using X-ray diffraction (XRD). Successive attempts were also conducted for Pb(Mg_1/2W_1/2)O₃ (PMW) and Pb(Zn_1/2W_1/2)O₃ (PZW) by reacting PbO with the precursor compounds. Stages of phase development in the two compositions were also analyzed. The results are compared with those of another tungsten-containing perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) and its B-site precursor Fe₂WO₆. After PbO addition to the precursor powders, a perovskite phase formed directly (i.e., without any intermediate phases) in the case of PMW. For PbO + ½ZnWO₄, in contrast, the decomposition of ZnWO₄ and preferential reaction with PbO resulted in Pb₂WO₅ and ZnO, instead of the perovskite PZW.     

Structure and physical properties of tetragonal PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> solid solutions

The principal bond distances in the structure of tetragonal PbMg_1/3Nb_2/3O₃-PbTiO₃ (PMN-PT) solid solutions have been determined by the Rietveld method. The ferroelectric state of (PbMg_1/3Nb_2/3O₃)_0.62(PbTiO₃)_0.38 samples is shown to be governed by the displacement of the Pb ions from their ideal crystallographic site. In the frequency range 4000–5000 cm^?1, the refractive index of the samples is 2.70–2.75, as determined by the Kramers-Kronig method.     

Dielectric responses in Mg<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>-replaced Pb[(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>),Ti]O<Subscript>3</Subscript> ceramics

Octahedral lattice sites of Pb[(Zn_1/3Nb_2/3),Ti]O₃ were replaced by 20 at.% Mg_1/3Ta_2/3 complex to enhance perovskite development, especially at Pb(Zn_1/3Nb_2/3)O₃-rich compositions. Resultant changes in the perovskite formation and associated dielectric responses were investigated. A perovskite structure was identified at Pb(Zn_1/3Nb_2/3)O₃-rich compositions by X-ray diffraction, although the development was rather incomplete. Phase transition modes in the dielectric constant spectra changed from diffuse to sharp ones, regardless of the introduction of Mg_1/3Ta_2/3. Dielectric maximum temperatures of the ceramics shifted linearly with the compositional change.     

Phase equilibrium and properties of solid solutions of PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>-PbNb<Subscript>2/3</Subscript>Mg<Subscript>1/3</Subscript>O<Subscript>3</Subscript>-PbGeO<Subscript>3</Subscript> system

Phase diagrams of three sections of the four-component system PbTiO₃-PbZrO₃-PbNb_2/3Mg_1/3O₃-PbGeO₃ are plotted (at 20°C) and electrophysical properties of solid solutions are studied. It is found that morphotropic areas, in which dielectric, piezoelectric, and elastic properties are extreme, have a wider concentration interval than in binary systems serving as the base for the studied solid solutions. In monophase areas, isosymmetrical fields (phase states) divided by areas of constant structural parameters are revealed. An explanation of the observed effects based on the real defect structure of objects is proposed.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.     

Synthesis and characterization of pseudo-ternary Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ferroelectric ceramics via a B-site oxide mixing route

Perovskite phase formation and dielectric/ferroelectric properties of the pseudo-ternary Pb(Fe_1/2Nb_1/2)O₃-PbZrO₃-PbTiO₃ (PFN-PZ-PT) ferroelectric ceramics have been investigated as promising materials for multi-layer ceramic capacitors. Complete solid solution with pure perovskite phase can be formed in this system in the whole composition range studied using conventional solid-state reaction method via a B-site oxide mixing route. Crystal lattice of the ceramics obtained shrinkages with the increase of the concentration of Pb(Fe_1/2Nb_1/2)O₃ (PFN) and expands with the increase of the content of PbZrO₃ (PZ). With the increase of the concentration of PbTiO₃ (PT), crystal structure of PFN-PZ-PT changes from pseudo-cubic ferroelectric phase to tetragonal one while retains the fraction of PFN as constant. A morphotropic phase boundary (MPB) forms at the composition of 42 mol% PT regardless of whatever concentration of PFN, and the content of PFN affects little on the composition of MPB. The preliminary phase diagram of the PFN-PZ-PT system is determined by X-ray diffraction (XRD) measurements combining with dielectric/ferroelectric characterization. Dielectric measurements indicate that the value of dielectric maximum (ɛ_m) and the temperature where ɛ_m appears (T_m) increase with the increase of the concentration of PT. However, PFN exhibits opposite effects, i.e., ɛ_m increases with the increase of the concentration of PFN accompanied by the decrease of T_m.     

Subsolidus phase relations in the system Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Rh<Subscript>2</Subscript>O<Subscript>3</Subscript>

The Tm₂O₃-Rh₂O₃ system has been studied by x-ray diffraction, thermal analysis, and chemical analysis of annealed and quenched samples. The results have been used to construct a schematic subsolidus phase diagram of the system. Only one double oxide, TmRhO₃, has been identified. Some of its physicochemical properties are reported.     

Glass formation in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO system

The physicochemical properties of BaO-Bi₂O₃-B₂O₃ glasses have been studied. The effect of KBF₄ additions on the properties of the glasses has been examined. The transmission of the glasses has been correlated with their local structure and composition.     

Calcium bismuth borates in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The 600°C (subsolidus) section of the CaO-Bi₂O₃-B₂O₃ phase diagram has been studied by x-ray diffraction and differential thermal analysis. A new calcium bismuth borate of composition CaBi₂B₄O₁₀ has been identified, and the existence of CaBi₂B₂O₇ has been confirmed. According to T-x phase diagram data, these compounds form peritectically at 700±5 and 783±5°C, respectively.     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Crystal structure,phonon characteristic,and intrinsic properties of Sm(Mg<Subscript>1/2</Subscript>Sn<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> double perovskite ceramic

Sm(Mg_1/2Sn_1/2)O₃(SMS) microwave dielectric ceramic was prepared by the traditional solid state synthesis method. The samples were tested by X-ray diffraction (XRD), vibrational spectra (Raman scattering and far-infrared reflectance spectroscopy). The Sm(Mg_1/2Sn_1/2)O₃ perovskite is monoclinic with the space group P2₁/n proved by XRD. Raman vibrational modes were fitted and assigned by Lorentz function. To calculate the intrinsic properties, far-infrared spectra with seven active modes were fitted using a four-parameter semi-quantitative (FPSQ) model. The dielectric constant calculated according to FPSQ is similar to that obtained from the molecular polarization and the Clausius equation. The intrinsic loss has been determined by the relationship between the damping factor and the spectral center frequency, which is slightly larger than the value obtained in the four-parameter fitting, and indicates that A_1g(Sm) Raman mode has a enormous effect on the dielectric loss. F_3u ⁽³⁾ and F_4u ⁽⁴⁾ have the greatest contribution to the dielectric constant and loss. Finally, the real and imaginary parts of permittivity were analyzed with Kramers-Krönig transformation.     

Electrical properties of perovskite-like compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> system

The electrical properties of layered perovskite-like compounds with the general formula Bi _{m + 1}Fe _{m − 3}Ti₃O_{3m + 3} have been studied in relation to their physicochemical properties and structure.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.     

Crystallization from high-temperature solutions in the K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied general trends of crystallization from high-temperature solutions in the K₂O-P₂O₅-V₂O₅-Bi₂O₃ system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi₂O₃ contents from 25 to 50 wt % and identified the stability regions of BiPO₄, K₃Bi₅(PO₄)₆, K₂Bi₃O(PO₄)₃, and K₃Bi₂(PO₄)_{3 ? x} (VO₄) _x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C ₂/c): K₃Bi₂(PO₄)₂(VO₄), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K₃Bi₂(PO₄)_1.25(VO₄)_1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Effect of excess PbO and sintering temperature on the templated grain growth of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)<Subscript>0.67</Subscript>Ti<Subscript>0.33</Subscript>O<Subscript>3</Subscript> polycrystals

The effect of excess lead oxide and sintering temperature on the microstructure evolution in the templated grain growth (TGG) of the Pb(Mg_1/3Nb_{2/ 3})_0.67Ti_0.33O₃ (PMNT67/33) polycrystals was investigated. By adding excess PbO in the precursor of PMNT ceramics, the textured structure of PMNT polycrystals was obtained near SrTiO₃ (ST) template by the conventional ceramic technique. The texture profiles developed progressively with increasing the concentration of excess PbO. A suitable sintering temperature is also very essential to grow a thick textured layer and avoid a second phase. Furthermore, the through-thickness of the PMNT textured layer is strongly influenced by the uniaxial compact-pressure of preparing the ST seeded PMNT specimen.