Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3–Pb(Zr/Ti)O3 Relaxors

The structure and dielectric properties of (1− x )Pb(Sc_2/3W_1/3)O₃–( x )Pb(Zr/Ti)O₃ ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x ≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc_2/3W_1/3)O₃ (PSW) can be described by a random-site model with one cation site occupied by Sc³⁺ and the other by a random distribution of (Sc_1/3³⁺W_2/3⁶⁺). The ordering is destabilized in solid solutions of PSW with PbZrO₃ (PSW–PZ), but stabilized by PbTiO₃ in the (1− x )PSW–( x )PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum ( T _ɛ,max) increases linearly with x ; however, for PSW–PT T _ɛ,max decreases in the ordered region (up to x = 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, T _ɛ,max increased by more than 60°C.     

Crystal Structure and Related Properties of Manganese-Doped Barium Titanate Ceramics

The influence of manganese on the crystallographic phase and the microstructure of BaTi_{1− x} Mn _x O₃ ceramics (0 ≤ x ≤ 0.05) is investigated. The crystal structure at room temperature changes from tetragonal to hexagonal between x = 0.005 and 0.017, which causes a drastic change in the microstructure. The Jahn_Teller distortion caused by the Mn_Ti³⁺ ions is proposed as the driving force for the phase transition. Annealing of the as-fired samples in both a reducing and oxidizing atmosphere restores the tetragonal phase, which is accompanied by a change in the microstructure based on the percentage of tetragonal phase.     

Formation and Structural Characterization of 1:1 Ordered Perovskites in the Ba(Zn1/3Ta2/3)O3–BaZrO3 System

The phase stabilities in the(1−x)Ba(Zn_1/3Ta_2/3)O₃ (BZT)-xBaZrO₃(BZ)system have been investigated using samples prepared by the mixed oxide method. The substitution of Zr⁴⁺destabilizes the 1:2 cation ordering in BZT and pro-motes the formation of a cubic, 1:1 ordered structure with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions beyond this range stabilize a disordered perovskite. The limits of stability of the 1:1 ordering coin-cide with compositions previously found to exhibit anoma-lies in their dielectric loss. The range of homogeneity is consistent with a "random layer" model for the 1:1 ordered "Ba{β';_1/2β^1/2}O₃" structure. In this model the B× positions are assumed to be occupied exclusively by Ta⁵⁺, and the b× sites by a random distribution of Zn₂₊, Zr₄₊, and the remaining Ta 5+ cations. The validity of the model, where the ordered solid solutions can be represented by Ba{[Zn_{2− y /3}Ta_{(1−2 y )/3}Zr y ]_1/2[Ta]_1/2}O₃(y =2x)was con-firmed by Rietveld refinements conducted using data col-lected with a synchrotron X-ray source.     

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.     

X-ray Diffraction and 151Eu Mössbauer Spectroscopic Study of the Hf1−xEuxO2−x/2(0 ≤x≤ 1.0) System

Powder X-ray diffractometry (XRD) and ¹⁵¹Eu Mössbauer spectroscopy were performed for samples prepared in the temperature range 1500–1500°C for the hafnia–europia (HfO₂–Eu₂O₃) system Eu _x Hf_{1− x} O_{2− x /2}(0 ≤ x ≤ 1.0). The XRD results showed that two types of solid solution phases formed in the composition range 0.25 ≤ x ≤ 0.725: an ordered pyrochlore-type phase in the middle-composition range (0.45 < x < 0.575) and a disordered fluorite-type phase, enveloping the pyrochlore-type phase on both sides, in the composition ranges 0.25 ≤ x ≤ 0.40 and 0.60 ≤ x ≤ 0.725. ¹⁵¹Eu Mössbauer spectroscopy sensitively probes local environmental changes around trivalent europium (Eu³⁺) caused by the formation of these solid solution phases. In addition to the broad, single Mössbauer spectra observed in this study for the Eu³⁺, the values of isomer shift (IS) exhibited a pronounced minimum in the neighborhood of the stoichiometric pyrochlore phase ( x ≈ 0.5). Such IS behavior of Eu³⁺ was interpreted based on the XRD crystallographic information that the ordered pyrochlore phase has a longer (in fact, the longest) average Eu–O bond length than those of the disordered fluorite phases on both sides or the monoclinic (and C-type) Eu₂O₃at x = 1.0.     

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.     

Relationship between Doping and Ordering (1/3<111> and 1/2<111> Types) in A(B2+B5+)O3 and A(B3+B6+)O3 Systems

The Madelung energies of A²⁺ (B_1/3²⁺ B_2/3⁵⁺) O₃^2- and A²⁺ (B_2/3³⁺ B_1/3⁶⁺) O₃^2- systems were calculated for different dopants on the A-site. The theoretical results show that the higher-valence dopant enhances the 1/2<111>-type (1:1) ordered arrangement of B-site cations in A²⁺ (B_1/3²⁺ B_2/3²⁺)O₃^2-, whereas the lower-valence dopant promotes the 1:1 ordering in A²⁺ (B_2/3³⁺ B_1/3⁶⁺)O₃^2-, and no doping promotes the 1/3<111>-type (1:2) ordering in the both systems. These calculation results are in agreement with the experimental observations of donor- and acceptor-doped PMN systems.     

Dielectric and Electrical Conductivity Properties of PMS–PZT Ceramics

The dielectric and electrical conductivity properties of x Pb(Mn_1/3Sb_2/3)O₃–(1− x )Pb(Zr_0.52Ti_0.48)O₃ (PMS–PZT) ceramics were studied. X-ray diffraction indicated that all samples exhibit a single-phase perovskite structure. Dielectric study revealed that the dielectric relaxor behavior was induced by co-doping Mn²⁺ and Sb⁵⁺ into Pb(Zr_0.52Ti_0.48)O₃ ceramics. Electrical conductivity measurements showed that the concentration of carriers are increased with the increase in PMS contents. After annealing in an oxygen atmosphere for 30 h, the direct current conductivity of PMSZ15 was much lower than that of the as-sintered sample. The reason why this phenomenon occurs may be the reduction of oxygen-vacancy concentration.     

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.     

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.     

Crystal Chemistry and Phase Transitions in Substituted Pollucites along the CsAlSi2O6-CsTiSi2O6.5 Join: A Powder Synchrotron X-ray Diffractometry Study

The crystal structures for a suite of substituted pollucites with the compositions CsTi _x Al_{1– x} Si₂O_{6+0.5 x} , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi₂O₆) has a tetragonal structure (space group I 4₁/ a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O²⁻ anions (needed for compensating the charge imbalance between Ti⁴⁺ and Al³⁺), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi_0.1Al_0.9Si₂O_6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating.     

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.     

Fatigue-Free Lead Zirconate Titanate (Pb(Zr,Ti)O3)-Based Capacitors Co-modified by Lanthanum and Lithium for Nonvolatile Memories

Pb_0.98(La_{1− x} Li _x )_0.02(Zr_0.55Ti_0.45)O₃(PLLZT with 0.1 ≤ x ≤ 0.7) thin films were sol-gel-grown on Pt(111)/Ti/SiO₂/Si substrates, employing a thin lead zirconate titanate (PZT) template layer. Films annealed at >550°C showed a highly (111)-oriented preferential growth. Typical values of the switchable remanent polarization (2 P _r) and the coercive field ( E _c) of the PLLZT/PZT/Pt film capacitor for x = 0.3 were 50 μC/cm² and 39 kV/cm, respectively, at 5 V. All the PLLZT/PZT/Pt capacitors (for 0.1 ≤ x ≤ 0.7) exhibited fatigue-free behavior up to 6.5 × 10¹⁰ switching cycles, a quite stable charge retention profile with time, and high 2 P _rvalues, all which assure their suitability for nonvolatile ferroelectric memories.     

Sintering Behavior, Phase Evolution, and Microwave Dielectric Properties of Bi(Sb1−xTax)O4 Ceramics

Sintering behavior, phase evolution, and microwave dielectric properties of Bi(Sb_{1− x} Ta _x )O₄ ceramics (0.05≤ x ≤0.60) were studied and their relationships were discussed in detail. Phase studies revealed that a pure monoclinic phase could be formed when x ≤0.20 and a pure orthorhombic phase could be obtained when x ≥0.50. As the x value increased from 0.05 to 0.60, the densified temperature of Bi(Sb_{1− x} Ta _x )O₄ ceramics decreased from 1050° to about 960°C whereas the density increased from 8.07 to 8.41 g/cm³. The microwave dielectric constant increased from 20.5 to 34 whereas the Q × f value decreased from 60 000 to 29 000 GHz. In the monoclinic phase region, the temperature coefficients of resonant frequency shifted linearly from −58 to −45 ppm/°C as the x value increased from 0.05 to 0.2 and then remained constant at about −12 ppm/°C when x ≥0.40. The Bi(Sb_{1− x} Ta _x )O₄ ceramics are promising for application of low-temperature cofired ceramics technology.     

Structure and Dielectric Properties of the Ba(Mg1/3Nb2/3)O3-La(Mg2/3Nb1/3)O3 System

A complete range of perovskite solid solutions can be formed in the (1 − x )Ba(Mg_1/3Nb_2/3)O₃- x La(Mg_2/3Nb_1/3)O₃ (BMN-LMN) pseudobinary system. While pure BMN adopts a 1:2 cation ordered structure, 1:1 ordered phases are stabilized for 0.05 ≤ x ≤ 1.0. Dark-field TEM images indicate that the La-doped solid solutions are comprised of large 1:1 ordered domains and no evidence was found for a phase-separated structure. This observation coupled with the systematic variations in the intensities of the supercell reflections supports a charge-balanced "random-site" model for the 1:1 ordering. The substitution of La also induces a transformation from a negative to positive temperature coefficient of capacitance in the region 0.25 ≤ x ≤ 0.5.     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Electrical Properties of Cerium-Doped BaTiO3

The high-temperature equilibrium electrical conductivity of Ce-doped BaTiO₃ was studied in terms of oxygen partial pressure, P (O₂), and composition. In (Ba_1−xCe _x )TiO₃, the conductivity follows the −1/4 power dependence of P (O₂) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P (O₂) where electron compensation prevails at low P (O₂). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO₃, indicating the substitution of Ce as Ce⁴⁺ for Ti⁴⁺ in Ba(Ti_1−yCe _y )O₃. The Curie temperature ( T _c) was systematically lowered when Ce³⁺ was incorporated into Ba²⁺ sites, whereas the substitution of Ce⁴⁺ for Ti⁴⁺ sites resulted in no change in this parameter.     

Methane Oxidation on Perovskite-Type Ca(Mn1−xTix)O3−δ

X-ray photoelectron spectroscopy was performed to elucidate the catalytic activity of CH₄ oxidation on perovskite-type Ca(Mn_{1− x} Ti _x )O_3−δ synthesized at 1173 K in a flow of oxygen from a gel with citric acid and ethylene glycol. The Mn ion content decreases and the ratio of the Mn³⁺ ion in the Mn ion increases with increases in x . Ca(Mn_{1− x} Ti _x )O_3−δ has a high catalytic activity of CH₄ oxidation at x =0.4. These results indicate that the catalytic activity strongly depends on the Mn³⁺ ion content of the surface.     

Energetics of Substituted Pollucites Along the CsAlSi2O6–CsTiSi2O6.5 Join: A High-Temperature Calorimetric Study

Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTi _x Al_{1− x} Si₂O_{6+0.5 x} , 0 ≤ x ≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B₂O₃) at 701°C. As Ti⁴⁺ substitutes for Al³⁺, the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x = 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short-range order associated with the framework cations Al³⁺, Si⁴⁺, and Ti⁴⁺ in the structure. Using enthalpies of drop solution of SiO₂, Al₂O₃, TiO₂, and Cs₂O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time.     

Oxygen Potentials of (Am0.5Np0.5)O2−x

The oxygen potentials of the oxygen-deficient fluorite-type oxide (Am_0.5Np_0.5)O_{2− x} were measured by the electrochemical method using a zirconia solid electrolyte. Coulomb titration has been performed for the sample at 1333 K over 0.021≤ x ≤0.25. The oxygen potentials were −93.63 and −440.18 kJ/mol for x =0.021 and 0.25 at 1333 K, respectively. The temperature dependence of the oxygen potentials was also measured between 1000 and 1333 K over the x range of 0.021≤ x ≤0.243. The temperature dependence was almost linear over the x and temperature ranges concerned.