Effect of addition of Ba(W0.5Cu0.5)O3 in Pb(Mg1/3Nb2/3)O3-Pb(Zn1/3Nb2/3)O3-Pb(Zr0.52Ti0.48)O3 ceramics on the sintering temperature, electrical properties and phase transition

In this work, we report on the Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramics with Ba(W_0.5Cu_0.5)O₃ as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W_0.5Cu_0.5)O₃ significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W_0.5Cu_0.5)O₃-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: (K_p = 0.63, Q_m = 1415 and d₃₃ = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications.     

Rhombohedral-monoclinic phase transition related to grain orientation in Zr-rich Pb(ZrxTi1−x)O3 thin films

Pb(Zr_xTi_1−x)O₃ thin films with mixed orientations of (1 1 1) and (1 0 0) were prepared on Pt/Ti/SiO₂/Si substrate by sol-gel technique. The compositions of PZT thin films are chosen as x = 0.55 and x = 0.58. Both of the compositions are in the rhombohedral phase region of the Pb(Zr_xTi_1−x)O₃ phase diagram, but the former is near the monoclinic phase existence region, and the latter is far from the monoclinic phase existence region. Rhombohedral-monoclinic phase transitions are reported in both of the thin films. The results show that the phase transition is related to the grain orientation. Phase transitions in the films are clearly identified: rhombohedral phase transforms to M_B phase in (1 1 1)-oriented grains, and rhombohedral phase transforms to M_A phase in (1 0 0)-oriented grains. The remnant polarization is determined by the content of (1 1 1)-oriented grains. It is shown that the remnant polarization is greater in the film with higher content of (1 1 1)-oriented grains.     

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg1/3Nb2/3)TiO3–xPbTiO3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg_1/3Nb_2/3)TiO₃–xPbTiO₃ is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.     

Additional transition induced by magnetoelectric interaction in ferroelectromagnet Pb（Fe1/2Nb1/2）O3

Besides the two phase transitions known in ferroelectromagnets, an additional transition was observed experimentally in Pb（Fe1/2Nb1/2）O3 and the possible mechanism was explored. The magnetic moment shows that anomalous increases when the temperature goes down away from the Neel temperature of 20-30 K. The existence of the hysteresis verifies the weak ferromagnetic property. This additional phase transition is considered to originate from the magnetoelectric coupling between the ferroelectric and antiferromagnetic orders in this compound. From the Moessbauer parameter analysis, it is confirmed that the hybridization of the O 2p, Fe 3d and Nb 4d electron states makes the realization of magnetoelectric coupling possible.     

Effects of TiC addition on formation of Ti3SiC2 by self-propagating high-temperature synthesis

Formation of Ti₃SiC₂ was conducted by self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Si:C = 3:1:2 and the TiC-containing samples compressed from powder mixtures of Ti/Si/C/TiC with TiC content ranging from 4.3 to 33.3 mol%. The effect of TiC addition was studied on combustion characteristics and the degree of phase conversion. For the elemental powder compacts, with the progress of combustion wave the sample experiences substantial deformation, including axial elongation and radial contraction. The extent of sample deformation and flame-front propagation velocity were considerably reduced for the samples with TiC addition, because the dilution effect of TiC lowered the reaction temperature. Two reaction mechanisms were adopted to explain the formation of Ti₃SiC₂, one involving the reaction of a Ti–Si liquid phase with solid reactants for the elemental powder compact and the other dominated by the interaction of solid-phase species for the TiC-containing sample. For all products synthesized in this study, the XRD analysis identifies formation of Ti₃SiC₂ along with a major impurity TiC and a small amount of Ti₅Si₃. The resulting Ti₃SiC₂ is typically elongated grains. Based upon the XRD profile, the Ti₃SiC₂ content at a level of 71.5 vol.% was obtained in the product from the elemental powder compact. With the addition of TiC, an improvement in the yield of Ti₃SiC₂ was observed and an optimal conversion reaching 85 vol.% was achieved by the sample with 20 mol% of TiC. However, further increase of the TiC amount led to a decrease in the Ti₃SiC₂ content, because of the low reaction temperature around 1150 °C.     

Relationship between structure and properties in high-temperature Bi(Al0.5Fe0.5)O3-PbTiO3 piezoelectric ceramics

Ceramic samples of xBi(Al_0.5Fe_0.5)O₃-(1 − x)PbTiO₃ (BAF-PT, x = 0.05-0.5) solid solutions were fabricated using the conventional solid state reaction method. X-ray diffraction analysis revealed that all compositions can form single perovskite phase with tetragonal symmetry. The relationship between the tetragonal lattice parameters, tetragonality c/a, cell volume, and ferro-piezoelectric characterization as a function of x was systematically investigated. The BAF modification can effectively improve the poling condition at a proper BAF content. A combination of piezoelectric constant of d₃₃ (50-60 pC/N), electromechanical planar coupling coefficients of k_p (20.3-22.5%), and high Curie temperature T_c (>478 °C) suggested that BAF-PT could be a good candidate for high-temperature piezoelectric applications.     

Study on phase formation and sintering kinetics of BaTi0.6Zr0.4O3 powder synthesized through modified chemical route

BaTi_0.6Zr_0.4O₃ powder was prepared from barium oxalate hydrate, zirconium oxy-hydroxide and titanium dioxide precursors. Barium oxalate hydrate and zirconium oxy-hydroxide were precipitated from nitrate solution onto the surface of suspended TiO₂. Phase formation behaviour of the materials was extensively studied using XRD. BaTiO₃ (BT) and BaZrO₃ (BZ) start forming separately in the system upon calcinations in the temperature range 600–700 °C. BT–BZ solid solution then forms by diffusion of BT into BZ from 1050 °C onwards. The precursor completely transforms into BaTi_0.6Zr_0.4O₃ (BTZ) at 1200 °C for 2 h calcination. The activation energy (AE) of BT (134 kJ mol⁻¹) formation was found to be less than that of BZ (167.5 kJ mol⁻¹) formation. BTZ formation requires 503.6 kJ mol⁻¹ of energy. The sintering kinetics of the powder was studied using thermal analyzer. The mean activation energy for sintering was found to be 550 kJ mol⁻¹.     

Relationship between dielectric properties and structural long-range order in (x)Pb(In1/2Nb1/2)O3:(1 − x)Pb(Mg1/3Nb2/3)O3 relaxor ceramics

The dielectric and structural order–disorder properties of as-sintered complex perovskite (x)Pb(In_1/2Nb_1/2)O₃:(1 − x)Pb(Mg_1/3Nb_2/3)O₃ ceramics are highly influenced by the quantity of Pb(In_1/2Nb_1/2)O₃ (PIN). A high PIN quantity causes the relative permittivity maxima (ε_max) to decrease and the temperature (T_max) to increase. Also, strong frequency dispersion is dominant in the relative permittivity when plotted against the temperature. In ferroelectric hysteresis loop measurements, the maximum values of electric displacements (D_max) decrease with increasing PIN. The ceramics in the composition range x = 0.1–0.8 behave as ferroelectric relaxors and exhibit very slim hysteresis loops for all these compositions. Transmission electron microscopy (TEM) studies show that the size of the 1:1 structural ordered domains is influenced by the PIN quantity. The relationship between the dielectric properties and the long-range 1:1 order in these relaxors appear to be in conflict with the commonly accepted order–disorder behavior in complex perovskite ferroelectrics, in which large structural domains correspond with the tendency to depart from the relaxor state. TEM observations show that individual 1:1 ordered domains in (x)PIN:(1 − x)PMN ceramics are composed of numerous nano-sized ordered domains, separated by fine antiphase boundaries.     

Microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric resonators

Ba(Zn_1/3Ta_2/3)O₃ (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO₃, ZnO, and Ta₂O₅ powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications.     

Impedance and electric modulus analysis of Sm-modified Pb(Zr0.55Ti0.45)1−x/4O3 ceramics

The polycrystalline ceramic samples of Pb_1−xSm_x(Zr_0.55Ti_0.45)_1−x/4O₃ (x = 0.00, 0.03, 0.06 and 0.09) were prepared by solid-state reaction technique at high temperature. Electric impedance (Z) and modulus (M) properties of the materials have been investigated within a wide range of temperature and frequency using complex impedance spectroscopy (CIS) technique. The complex impedance analysis has suggested the presence of mostly bulk resistive (grain) contributions in the materials. This bulk resistance is found to decrease with the increase in temperature. It indicates that the PSZT compounds exhibit a typical negative temperature coefficient of resistance (NTCR) behavior. The bulk contribution also exhibits an increasing trend with the increase in Sm³⁺ substitution to PZT. The complex modulus plots have confirmed the presence of grain (bulk) as well as grain boundary contributions in the materials. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the materials.     

Synthesis, structural, dielectric and electrical impedance study of Pb(Cu1/3Nb2/3)O3

Lead copper niobate Pb(Cu_1/3Nb_2/3)O₃ (PCN) prepared by the columbite precursor method and structurally characterized using X-ray diffraction analysis. The final phase X-ray diffraction diagram shows that final phase material has perovskite structure with pyrochlore phase. Temperature dependent of ′ and ″ shows that the compound exhibit dielectric anomaly in the studied temperature range. Impedance spectroscopy used to characterize the electrical behaviour. ac impedance spectrum results indicate that the relaxation mechanism of the material is temperature dependent and has dominant bulk contribution in different temperature ranges. Frequency dependence of the real (′) and imaginary (′′) part of the dielectric permittivity shows typical characteristic of ferroelectric materials. Temperature dependent of dc resistively shows that resistance decreases with the increase in temperature and follows Arrhenius behaviour in different temperature regions.     

Effect of Ln2O3 (Ln = La, Pr, Eu, Gd) addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics

(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics added with 0.2 wt.% Ln₂O₃ (Ln = La, Pr, Eu, Gd) were prepared by a citrate method, and the structure and electrical properties of the ceramics were investigated with respect to the size of the lanthanide. All the specimens maintain a coexistence of rhombohedral and tetragonal phases in crystal structure, while no remarkable evolution in microstructure with the lanthanide addition was observed. Compared with (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃, the lanthanide addition resulted in an increased diffuseness in phase transition and a decrease in depolarization temperature (T_d). The variation in dielectric, piezoelectric and ferroelectric properties with the lanthanide addition presents an evident lanthanide size dependence. The addition of La₂O₃ or Pr₂O₃ tailored the electrical properties basically following a soft doping effect, with the specimens added with La₂O₃ and Pr₂O₃ attaining high piezoelectric constants (d₃₃) of 188 and 184 pC/N, respectively. By contrast, the Eu₂O₃ or Gd₂O₃ addition led to an abnormal change in the electrical properties, which was qualitatively interpreted by an internal stress effect.     

Structural and electrical properties of Gd(Ni1/2Zr1/2)O3

The Gd(Ni_1/2Zr_1/2)O₃ (GNZ) ceramic is synthesized by the solid-state reaction technique. The X-ray diffraction pattern of the sample shows monoclinic phase at room temperature. The dielectric dispersion of the material is investigated in the temperature range from 303 K to 673 K and in the frequency range from 100 Hz to 1 MHz. The relaxation peak is observed in the frequency dependence of the loss tangent. The relaxation time at different temperatures is found to obey Arrhenius law having activation energy of 1.1 eV which indicates the hopping of ions at the lattice site and may be responsible for the dielectric relaxation of GNZ. The scaling behaviour of loss tangent suggests that the relaxation mechanism is temperature independent. The frequency dependent conductivity spectra follow the power law. In the impedance formalism, the Cole-Cole model is used to study the relaxation mechanism of GNZ.     

Effect of CuO on the sintering temperature and piezoelectric properties of MnO2-doped 0.75Pb(Zr0.47Ti0.53)O3-0.25Pb(Zn1/3Nb2/3)O3 ceramics

The sintering temperature of 0.75Pb(Zr_0.47Ti_0.53)O₃-0.25Pb(Zn_1/3Nb_2/3)O₃ ceramics containing 1.5 mol% MnO₂ was decreased from 930 to 850 °C with the addition of CuO. The CuO reacted with the PbO and formed a liquid phase during the sintering, which assisted the densification of the specimens. Most of the Cu²⁺ ions existed in the CuO second phase, thereby preventing any possible hardening effect from the Cu²⁺ ions. Variations of the k_p, Q_m, ?₃^T/?₀ and d₃₃ values with CuO were similar to that of the relative density. The specimen containing 0.5 mol% CuO sintered at 850 °C showed the good piezoelectric properties of k_p = 0.5, Q_m = 1000, ?₃^T/?₀ = 1750 and d₃₃ = 300 pC/N.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

New dielectric material system of La(Mg1/2Ti1/2)O3–Ca0.6La0.8/3TiO3 for microwave applications

The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. 0.6La(Mg_1/2Ti_1/2)O₃–0.4Ca_0.6La_0.8/3TiO₃ ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (_r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Phase structure and electrical properties of (0.8 − x) BaTiO3-0.2Bi0.5Na0.5TiO3-xBaZrO3 lead-free piezoceramics

Lead-free piezoelectric ceramics (0.8 − x)BaTiO₃-0.2Bi_0.5Na_0.5TiO₃-xBaZrO₃ (BT-BNT-xBZ, 0 ≤ x ≤ 0.08) doped with 0.3 wt% Li₂CO₃ were prepared by conventional solid-state reaction method. With the Li₂CO₃ doping, all the ceramics can be well sintered at 1170-1210 °C. The phase structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between tetragonal and pseudocubic phases exists at x = 0.03-0.04. The addition of Zr can improve the piezoelectric properties of BT-BNT ceramics. Furthermore, a relaxor behavior is induced and the tetragonal-cubic phase transition shifts towards lower temperatures after the addition of Zr. The ceramics with x = 0.03 possess the optimum electrical properties: d₃₃ = 72 pC/N, k_p = 15.4%, ?_r = 661, P_r = 18.5 μC/cm², E_c = 34.1 kV/cm, T_c = 150 °C.     

Ni2Cr(BO3)O2涂层的制备及其红外发射性能

通过喷雾造粒和高温焙烧制备Ni_2Cr(BO_3)O_2粉末后利用等离子喷涂得到一种高红外发射涂层,并研究了该种涂层的红外发射性能。SEM观察涂层的表面、断面形貌,发现涂层与基体结合紧密、无脱落;XRD对焙烧后的粉末物相组成进行了表征,主要以Ni_2Cr(BO_3)O_2为主。对涂层红外波段发射率的测试表明,在0.76~2.5μm波段的发射率为0.896、2.5~14μm波段发射率为0.925,具有优异的红外发射性能。Ni_2Cr(BO_3)O_2晶胞内的畸变、非对称性以及电子转移跃迁是导致Ni_2Cr(BO_3)O_2这种材料具有高红外发射率的主要原因。Ni_2Cr(BO_3)O_2涂层能够经受37次"900℃~水冷"热震循环。该种涂层由于其高红外发射性能、优异的耐热震性能和热稳定性能而具有较高的实用价值。     

Phase transition and electrical properties of (1 − x)K0.02Na0.98NbO3-xBaTiO3 ceramics

(1 − x)K_0.02Na_0.98NbO₃-xBaTiO₃ ceramics were prepared by the solid state reaction method, and their electrical properties were investigated. The samples showed crystal structure changing from monoclinic to orthorhombic, and then to tetragonal, with an increase in BaTiO₃ content. The addition of BaTiO₃ markedly enhanced ferroelectric and piezoelectric properties of K_0.02Na_0.98NbO₃ ceramics. Remnant polarization increased and coercive field decreased only in the samples with small amount of BaTiO₃. Piezoelectric properties were improved with the addition of BaTiO₃. The 0.9K_0.02Na_0.98NbO₃-0.1BaTiO₃ ceramics showed maximum piezoelectric constant (d₃₃ = 160 pC/N), which was even comparable with that of (1 − x)K_0.5Na_0.5NbO₃-xBaTiO₃ ceramics. Their good piezoelectric properties, along with a low ferroelectric-ferroelectric transition temperature (T_F-F), made the 0.9K_0.02Na_0.98NbO₃-0.1BaTiO₃ ceramics a potential candidate for lead-free piezoelectric applications.