Dielectric-State Analysis in Solid-Solution Pb(Yb1/2Ta1/2)O3–Pb(Lu1/2Nb1/2)O3

The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb_1/2Ta_1/2)O₃– x Pb(Lu_1/2Nb_1/2)O₃. Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ).     

BiScO3 Doped (Na0.5K0.5)NbO3 Lead-Free Piezoelectric Ceramics

Lead-free potassium sodium niobate-based piezoelectric ceramics (1− x )(Na_0.5K_0.5)NbO₃– x BiScO₃ (KNN–BS) ( x =0∼0.05) have been prepared by an ordinary sintering process. Single perovskite phase of KNN–BS exhibits an orthorhombic symmetry at x <0.015 and pseudocubic symmetry at x >0.02, separating by a MPB at 0.015≤ x ≤0.02. Piezoelectric and ferroelectric properties are significantly enhanced in the MPB, which are as follows: piezoelectric constant d ₃₃=203 pC/N, planar coupling coefficient k _p=0.36, remnant polarization P _r=24.4 μC/cm². These solid solution ceramics look promising as a potential lead-free candidate materials.     

Structure-Property Phase Diagram of BaZrxTi1−xO3 System

In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr _x Ti_{1− x} )O₃ system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr _x Ti_{1− x} O₃ system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO₃) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO₃). A comprehensive structure–property correlation of BaZr _x Ti_{1− x} O₃ ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram.     

Effect of BiScO3 and LiNbO3 on the Piezoelectric Properties of (Na0.5K0.5)NbO3 Ceramics

Lead-free potassium sodium niobate-based piezoelectric ceramics (1− y )(Na_{0.5−0.5 x} K_{0.5−0.5 x} Li _x )NbO₃− y BiScO₃ (  y =0.01, x= 0–0.06) have been prepared by an ordinary sintering process. The XRD analysis showed that the structure changes from orthorhombic to tetragonal with the increase of x (at y =0.01, abbreviated as KNNBSL100 x ). At room temperature, the polymorphic phase transition from the orthorhombic to the tetragonal phase was identified at approximately 0.02≤ x ≤0.04. The piezoelectric and ferroelectric properties were significantly enhanced. The temperature dependences of the relative permittivity revealed that the Curie temperature was increased with the addition of LiNbO₃. These solid solution ceramics are promising as potential lead-free candidate materials.     

Crystal Structure and Ferroelectric Properties of (Bi0.5Na0.5)TiO3–Ba(Zr0.05Ti0.95)O3 Piezoelectric Ceramics

The crystal structure and ferroelectric properties of (1− x )(Bi_0.5Na_0.5)TiO₃– x Ba(Zr_0.05Ti_0.95)O₃ (BNBZT x, x ≤12%) lead-free piezoelectric ceramics were studied. The distance between the centers of cations and anions ( d _c–a) as well as the lattice parameters was carefully investigated by Rietveld refinement on X-ray diffraction patterns. It was found that the crystal phase was determined by the amount of Ba(Zr_0.05Ti_0.95)O₃ added, whereas the pure rhombohedral and tetragonal phases are observed in compositions containing x ≤4 and x ≥8%, respectively. A rhombohedral–tetragonal morphotropic phase boundary (MPB) was found at around BNBZT6, which showed a maximum and minimum d _c–a at its rhombohedral and tetragonal phases, respectively. According to the present study, the ferroelectric properties show a strong dependence on their crystal phases. For the single-phase compositions, the remanent polarization ( P _r) generally increased with the value of d _c–a while their coercive fields ( E _c) were determined by their lattice parameters. Nevertheless, the behavior in P _r and E _c for MPB compositions is related to not only the lattice parameter but also the composed phases.     

Effects of La on Dielectric and Piezoelectric Properties of Pb1−xLa2x/3(Nb0.95Ti0.0625)2 O6 Ceramics

Ceramics with the chemical compositions of Pb_{1− x} La_{2 x /3}(Nb_0.95Ti_0.0625)₂O₆ (0≤ x ≤0.060) (PLTN) were prepared by the conventional solid-state reaction method. X-ray diffraction analysis indicated that Ti and La doping not only decreased the rhombohedral–tetragonal phase transformation temperature, but also stabilized the orthorhombic phase of PLTN ceramics. All ceramics sintered at 1190°–1250°C had shown the pure orthorhombic ferroelectric phase. La doping suppresses grain growth and inhibits the formation of pores and cracks, resulting in an increase in relative density up to 97%. The amount of La doping to PLTN ceramics obviously affect ceramics' piezoelectric constant ( d ₃₃) and dielectric loss (tanδ). The sample with x =0.015 possesses high Curie temperature ( T _c=560°C), low dielectric loss (tanδ=0.0054), and excellent piezoelectric constant ( d ₃₃=92 pC/N), presenting a high potential to be used in high-temperature applications as piezoelectric transducers.     

Dielectric and Piezoelectric Properties of the Morphotropic Phase Boundary Composition in the (0.8−x) Pb(Mg1/3Ta2/3)O3−0.2PbZrO3−xPbTiO3 Ternary System

Morphotropic phase boundary (MPB) compositions separating rhombohedral and tetragonal phases in the (1− x − y )Pb(Mg_1/3Ta_2/3)O₃– y PbZrO₃– x PbTiO₃ (PMT–PZ–PT100 x ) ternary solid solution system were characterized using X-ray diffraction and dielectric, piezoelectric properties. This work focused on compositions with a PZ content fixed at y =0.2, with an MPB composition found to be located at x =0.4. Piezoelectric coefficients and dielectric permittivity were found to be on the order of d ₃₃=580 pC/N and 4100, respectively. Acceptor modification using manganese was found to induce a "hardening" effect in 0.4PMT–0.2PZ–0.4PT, with decreased piezoelectric coefficients d ₃₃ and dielectric loss and increased mechanical quality factor Q . Piezoelectric coefficients d ₃₃, Q values, and dielectric loss were found to be 500 pC/N, 2000, and 0.4%, respectively, for 0.4PMT–0.2PZ–0.4PT with MnO₂ dopant levels around 0.5 wt%. The figure of merit (product of Q and d ₃₃) was found to be on the order of 1 × 10⁶, significantly higher when compared with other hard piezoelectric PZT materials. Specifically, the PMT–PZ–PT materials may be attractive candidates for high-power ultrasonic applications, particularly fine-scale components that require relating high permittivities.     

Structure and Microwave Dielectric Properties of (Zn1−xCox)TiO3 Ceramics

Dielectric ceramics in the system (Zn_{1− x} Co _x )TiO₃ ( x = 0–1) were synthesized by the solid-state reaction route. The phase distribution, microstructure, and dielectric properties were characterized by using powder X-ray diffraction analysis, electron microscopy, and microwave measurement techniques. Three phase composition regions were identified in the specimens sintered at 1150°C; [spinel + rutile] at 0 ≤ x ≤ 0.5, [spinel + ilmenite + rutile] at 0.5 < x ≤ 0.7, and [ilmenite] phase at 0.7 < x ≤ 1. For the 0 ≤ x ≤ 0.5 region, the amount of Ti-rich precipitates incorporated into the spinel phase decreased with the Co content at 0 ≤ x ≤ 0.5, with a concomitant increase of the rutile phase. The ilmenite phase appeared for high Co content. The microwave dielectric properties depended on the phase composition and volume according to the three phase regions, where the relative amount of rutile to the spinel or ilmenite determined the dielectric properties. The dielectric constant as a function of Co addition was modeled with a Maxwell mixing rule. An optimum phase distribution was determined in this system with dielectric constant of 25, a Q * f 70 000 GHz, and a low temperature coefficient of the resonant frequency.     

Phase Transitional Behavior and Piezoelectric Properties of Lead-Free (Na0.5K0.5)NbO3–(Bi0.5K0.5)TiO3 Ceramics

(1− x )(Na_0.5K_0.5)NbO₃–(Bi_0.5K_0.5)TiO₃ solid solution ceramics were successfully fabricated, exhibiting a continuous phase transition with changing x at room temperature from orthorhombic, to tetragonal, to cubic, and finally to tetragonal symmetries. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was found at 2–3 mol% (Bi_0.5K_0.5)TiO₃ (BKT), which brings about enhanced piezoelectric and electromechanical properties of piezoelectric constant d ₃₃=192 pC/N and planar electromechanical coupling coefficient k _p=45%. The MPB composition has a Curie temperature of 370°–380°C, comparable with that of the widely used PZT materials. These results demonstrate that this system is a promising lead-free piezoelectric candidate material.     

High Q Microwave Dielectric Ceramics in (Ni1−x Znx)Nb2O6 System

(Ni_{1− x} Zn _x )Nb₂O₆, 0≤ x ≤1.0, ceramics with >97% density were prepared by a conventional solid-state reaction, followed by sintering at 1200°–1300°C (depending on the value of x ). The XRD patterns of the sintered samples (0≤ x ≤1.0) revealed single-phase formation with a columbite ( Pbcn ) structure. The unit cell volume slightly increased with increasing Zn content ( x ). All the compositions showed high electrical resistivity (ρ_dc=1.6±0.3 × 10¹¹Ω·cm). The microwave (4–5 GHz) dielectric properties of (Ni_{1− x} Zn _x )Nb₂O₆ ceramics exhibited a significant dependence on the Zn content and to some extent on the morphology of the grains. As x was increased from 0 to 1, the average grain size monotonically increased from 7.6 to 21.2 μm and the microwave dielectric constant (ɛ'_r) increased from 23.6 to 26.1, while the quality factors ( Q _u× f ) increased from 18 900 to 103 730 GHz and the temperature coefficient of resonant frequency (τ_f) increased from −62 to −73 ppm/°C. In the present work, we report the highest observed values of Q _u× f =103 730 GHz, and ɛ'_r=26.1 for the ZnNb₂O₆-sintered ceramics.     

Microstructure and Microwave Dielectric Properties of (1−x)Ca(Mg1/3Ta2/3)O3/xCaTiO3 Ceramics

Dense (1− x )Ca(Mg_1/3Ta_2/3)O₃/ x CaTiO₃ ceramics (0.1≤ x ≤0.9) were prepared by a solid-state reaction process. The crystal structures and microstructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Single-phase solid solutions were obtained in the entire composition range. Long-range 1:2 ordering of B-site cations and oxygen octahedra tilting lead to the monoclinic symmetry with space group P 2₁/ c for x =0.1. For x above 0.1, the long-range ordering was destroyed and the crystal structure became the orthorhombic with space group Pbnm . The microwave dielectric properties showed a strong dependence on the composition and microstructure. The dielectric constant and temperature coefficient of resonant frequency increased nonlinearly as the CaTiO₃ content increased while the Qf values decreased approximately linearly. Good combination of microwave dielectric properties was obtained at x =0.45, where ɛ_r=45.1, Qf =34 800 GHz, and τ_f=17.4 ppm/°C.     

Crossover of Ba(Ti,Y)O3 Solid Solutions to Ba3Ti2YO8.5–BaTiO3 Composites and their Dielectric Properties

Ceramic samples with the nominal composition (1− x ) BaTiO₃+ x Ba₃Ti₂YO_8.5 ( x =0−0.535) were prepared by the mixed oxide method. X-ray diffraction (XRD) analysis shows that the materials are of single phase with a cubic symmetry as x ≤0.16. The compositions of the solid solutions ( x ≤0.16) can be expressed equivalently as Ba(Ti_{1− y} Y _y )O_3−δ ( y ≤0.122, y = x /(1+2 x )). For x >0.16, the materials are diphasic composites consisting of Ba(Ti_{1− y} Y _y )O₃ ( y =0.122) and Ba₃Ti₂YO_8.5. The microstructure observation by scanning electron microscopy supports the XRD result. The dielectric behavior and phase transitions of the solid solutions ( x ≤0.16) vary with different Y concentrations. The dielectric constant of the composites ( x >0.16) follows approximately the Lichteneker relation in a wide temperature range.     

Physical and Dielectric Properties of (1–x)PbZrO3·xBaTiO3 Thin Films Prepared by Chemical Solution Deposition

Physical and dielectric properties of (1– x )PbZrO₃· x BaTiO₃ thin films prepared by a chemical coating process have been investigated as a function of BaTiO₃ ( x ) content (0≤ x ≤0.2). Changing the molar ratio between propylene glycol and water prior to the deposition optimized the chemical precursors. (1– x )PbZrO₃- x BaTiO₃ thin films that contained a majority of perovskite phase, but also contained large amounts of other phases, were fabricated. These films could withstand fields of 250 kV/cm at 1 kHz. The microstructure of the thin films was found to depend on the BaTiO₃ content. The phase transition from antiferroelectric to ferroelectric was gradually induced as the BaTiO₃ content increased. A maximum dielectric constant of ∼809 was obtained at the composition of x = 0.1. A maximum dielectric constant of ∼809 was obtained at the composition of x = 0.1. A thin film at the low-field antiferroelectric-ferroelectric phase boundary with x = 0.05 exhibited the highest P _sat and P _r values. The maximum values of these were 45 and 31 μC/cm², respectively.     

Weakly Coupled Relaxor Behavior of BaTiO3–BiScO3 Ceramics

The structural and dielectric properties of (1− x )BaTiO₃– x BiScO₃ ( x =0–0.5) ceramics were investigated to acquire a better understanding of the binary system, including determination of the symmetry of the phases, the associated dielectric properties, and the differences in the roles of Bi₂O₃ and BiScO₃ substitutions in a BaTiO₃ solid solution. The solubility limit for BiScO₃ into the BaTiO₃ perovskite structure was determined to be about x =0.4. A systematic structural change from the ferroelectric tetragonal phase to a pseudo-cubic one was observed at about x =0.05–0.075 at room temperature. Dielectric measurements revealed a gradual change from proper ferroelectric behavior in pure BaTiO₃ to highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% BiScO₃. Several of the compositions showed high relative permittivities with low-temperature coefficients of capacitance over a wide range of temperature. Quantification of the relaxation behavior was obtained through the Vogel–Fulcher model, which yielded an activation energy of 0.2–0.3 eV. The attempt characteristic frequency was 10¹³ Hz and the freezing temperature, T _f, ranged from −177° to −93°C as a function of composition. The high coercive fields, low remanent polarization, and high activation energies suggest that in the BiScO₃–BaTiO₃ solid solutions, the polarization in nanopolar regions is weakly coupled from region to region, limiting the ability to obtain long-range dipole ordering in these relaxors under field-cooled conditions.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Electrical, X-Ray, and Thermal Expansion Studies in the System KNbO3-AgNbO3

Unlike the KNbO₃-NaNbO₃ system, the KNbO₃-AgNbO₃ system possessed a very limited degree of solid solution between its end-members. Solid solution of AgNbO₃ in KNbO₃ was limited to slightly less than 6 mole %, and solid solution of KNbO₃ in AgNbO₃ was limited to less than 0.5 mole %. Because of a tendency for the K_{1- x} Ag _x NbO₃ system to lose oxygen spontaneously during firing when 0.06 ≤ x ≤ 0.995, the system could not be treated as a true binary system. The compositions in the KNbO₃ solid solution region (0 ≤ x < 0.06) were ferroelectric at room temperature. Lattice parameter, relative permittivity, and thermal expansion measurements were made on specimens in the region 0 ≤ x ≤ 0.06.     

Quaternary Compounds Prepared in a CaO–Y2O3–SnO2 System

Compounds in a CaO–Y₂O₃–SnO₂ system were prepared by a solid-state reaction at 1673 K. The phase relation in this system was investigated by powder X-ray diffraction. Besides the previously reported ternary compounds, CaSnO₃, Ca₂SnO₄, Y₂Sn₂O₇, and a quaternary compound Ca_0.4Y_1.2Sn_0.4O₃, solid-solution series of Ca_{2− x} Y_{2 x} Sn_{1− x} O₄ with 0≤ x ≤0.5, and Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ with 0≤ y ≤0.2 and 0.95≤ y ≤1.0 were found. The cell parameters of these solid-solution series were refined. The changes of rhombohedral cell parameters in the samples prepared in the range 0.565< y <0.714 of Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ suggested the existence of solid solutions of Ca_0.4Y_1.2Sn_0.4O₃, although their single phases could not be prepared, except at y =0.6.     

Effects of Ca/Ti Cosubstitution upon Microwave Dielectric Characteristics of CaSmAlO4 Ceramics

(Ca_{1+ x} Sm_{1− x} )(Al_{1− x} Ti _x )O₄ (0≤ x ≤0.4) ceramics were synthesized by solid-state reaction method and their microstructures and microwave dielectric properties were investigated. X-ray diffraction analysis and energy-dispersive X-ray analysis indicated that the matrix phase was a solid solution with a composition represented by the chemical formula (Ca_{1+ x} Sm_{1− x} ) (Al_{1− x} Ti _x )O₄ and minor amount of (Ca,Sm)(Al,Ti)O₃ secondary phase was detected. Ca/Ti cosubstitution could significantly improve the microwave dielectric characteristics of CaSmAlO₄ ceramics, and the excellent microwave dielectric characteristics were obtained in the modified ceramics as ɛ_r=19–23, Q × f =49 100–118 700 GHz, and τ_f=−15–15 ppm/°C.     

Ferroelectric and Structural Properties of the Pb(Sc1/2Nb1/2)1-x,Tix,O3 System

Extensive solid solution was observed in the system Pb(Sc_1/2/,Nb_1/2,)_1-x,Ti_x,O₃. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO₃−PbTiO₃. The compound Pb(Sc_1/2Nb_1/2)O₃ exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc_1/2Nb_1/2)_0.575Ti_0.4250O₃. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohedral solid solution.