Dielectric, Ferroelectric and Piezoelectric Studies of PMN Modified PLZT Ceramics

Dielectric, ferroelectric and piezoelectric properties of xPb(Mg_1/3Nb_2/3)O₃-(1-x)(Pb_0.988 La_0.012)(Zr_0.535Ti_0.465)O₃ ceramic system synthesized through columbite precursor method are investigated. X-ray diffraction patterns of ceramics indicated pseudocubic phase formation with pyrochlore phase. Grain growth (4.47 μ m) and apparent density (7.68 gm/cm³) enhanced remarkably in 0.8PMN-0.2PLZT composition, respectively. Increasing PMN content remarkably increased both room temperature dielectric permittivity (ε_RT = 2316) and dielectric maximum (ε_Tc = 24747) in 0.6PMN-0.4PLZT composition, respectively. PMN substitution in PLZT system enhanced the ferroelectric remanent (P_r = 28.4 μ C/cm²) and spontaneous (P_s = 31.2 μ C/cm²) polarization while coercive field (E_c) continuously decreased in xPMN-(1-x)PLZT system. PMN modification in PLZT system influenced piezoelectric properties (d₃₃, k_p and k_t) throughout the PMN-PLZT system.     

Dielectric and ferroelectric properties of Ba(ZrxTi1−x)O3 ceramics

It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO₃-based system. In this study, barium zirconate titanate Ba(Zr_xTi_1−x)O₃ (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO₃-based compositions caused a decrease in Curie temperature (T_c). At T_c, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm² and 30 μC/cm², respectively.     

Dielectric and ferroelectric properties of lead indium niobate ceramic prepared by wolframite method

The dielectric and ferroelectric properties of lead indium niobate (Pb(In_1/2Nb_1/2)O₃, PIN) ceramic prepared by an oxide-mixing method via wolframite route were investigated. The 98.5% perovskite fine-grained PIN ceramics with average grain sizes of 1–2 μm were obtained by sintering at 1050 °C for 2 h. The dielectric properties of the PIN were of relaxor ferroelectric behavior with temperature of dielectric maximum (T_m) 53 °C and dielectric constant (_r) 4300 (at 1 kHz). The P–E hysteresis loop measurements at various temperatures showed that the ferroelectric properties of the PIN ceramic changed gradually from the paraelectric behavior at temperature above T_m to slim-loop type relaxor behavior at temperature below T_m. Moreover, the P–E loop became more open at temperatures much lower than T_m. At −25 °C, the maximum polarization is found to be 8 μm/cm² at a field of 30 kV/cm, with P_r value of 2.5 μm/cm² and E_c of +7.5 kV/cm.     

Hydrothermal synthesis of Ba(Ti, Sn)O3 fine powders and dielectric properties of the corresponding ceramics

Fine powders of submicron-sized crystallites of BaTiO₃ were prepared at 85–130°C by the hydrothermal method, starting from TiO₂.ξH₂O gel and Ba(OH)₂ solution. The products obtained below 110°C incorporated considerable amounts of H₂O and OH⁻ in the lattice. As-prepared BaTiO₃ is cubic and converts to the tetragonal phase after heat treatment at 1200°C, accompanied by the loss of residual OH⁻ ions. Hydrothermal reaction of SnO₂.ξH₂O gel with Ba(OH)₂ at 150–260°C gives rise to the hydrated phase, BaSn(OH)₆.3H₂O, due to the amphoteric nature of SnO₂.ξH₂O which stabilises Sn(OH)₆²⁻ anions in basic media. On heating in air or releasing the pressure in situ at 260°C, BaSn(OH)₆.3H₂O converts to BaSnO₃ through an intermediate, BaSnO(OH)₄. Solid solutions of Ba(Ti,Sn)O₃ are directly formed from (TiO₂ + SnO₂)..ξH₂O gel up to 35 mol% SnO₂. At higher Sn contents, the hydrothermal products are mixtures of BaSn(OH)₆.3H₂O and BaTiO₃, which on annealing at 1000°C result in monophasic Ba(Ti,Sn)O₃. The sintering characteristics and the dielectric properties of the ceramics prepared out of these fine powders are presented. The dielectric properties of fine-grained Ba(Ti,Sn)O₃ ceramics are explained on the basis of the prevailing diffuse phase transition behaviour.     

Growth of BA(TI1-xZRx)O3 single crystal fibers by laser heated pedestal growth technique

Ba(Ti_1-xZr_x)O₃ (x = 0.15 and 0.2) single crystal fibers were grown by the laser heated pedestal growth (LHPG) technique. The XRD results show that the grown crystals are of single phase. Temperature dependence of dielectric permittivity, room temperature hysteresis loops and strain were measured. A broad permittivity peak was observed with the temperature of the dielectric constant maximum T_m ≌ 339 K for x = 0.15, and T_m = 310 K for x = 0.2. The data were in agreement with those of corresponding ceramics, indicating that the compositions of the single crystals were similar to those starting stoichiometry (ceramics). The remnant polarization of 8.5 and 4.0 μC/cm² was obtained for x = 0.15 and 0.2, respectively. The strain level of ~0.065% and high field d₃₃ of ~ 130 pC/N for x = 0.15 were obtained.     

High-Permittivity Temperature-Stable Ceramic Dielectrics with Low Microwave Loss

The compounds SrZrO₃ and CaZrO₃ combine high permittivity with low loss and positive temperature coefficient of permittivity. Temperature-stable materials were produced by forming solid solutions between these zirconates and zirconates or titanates having negative coefficients. The properties of temperature-stable compositions in the systems Ca(Zr,Ti)O₃ and (Ba,Sr)(Zr,Ti)O₃ were investigated. At 4 GHz the relative permittivities were from 29 to 35 and the loss tangents from 3 to 11×10⁻⁴. Both permittivity and microwave loss increased as the principal alkaline-earth ion was changed from Ca to Sr to Ba, but the higher losses could be reduced by adding ∼1 mol% Nb or Ta. Dense fine-grained ceramics with the properties required for microwave applications were prepared.     

Dielectric, piezoelectric and pyroelectric properties of Pb(Zr, Ti)O3 ceramics elaborated by low temperature sintering with the aid of oxyfluoride additives

Pb(Zr, Ti)O₃ ceramics have been elaborated by low temperature sintering at 900°C with the aid of oxyfluoride additives. The mixture of PbO and PbF₂ (eutectic composition) allowed to achieve the densification of more than 98% of the theoretical density. The dielectric, piezoelectric and pyroelectric properties of thus obtained ceramics were investigated.     

Sm掺杂Pb(Mg1/3Nb2/3)O3-PZT压电陶瓷的研究

本文通过一步反应合成法制备了铌镁-锆钛酸铅(Pb(Mg_1/3Nb_2/3)O₃-Pb(Zr,Ti)O₃,PMN-PZT)压电陶瓷,研究了稀土元素钐(Sm)掺杂对PMN-PZT(x%(摩尔分数)Sm-PMN-PZT)结构与电学性能的影响规律,得到了具有高压电性、高机电耦合系数和高居里温度的压电陶瓷。当x=2.0时,压电常数d₃₃=611 pC/N,机电耦合系数k_p=0.68,介电损耗tan δ=1.65%,相对介电常数ε_r=2 650,居里温度T_C=283 ℃。测试压电陶瓷电致应变性能,在3 kV/mm下单极电致应变达到0.20%,显示出其大应变材料的特征。结果表明,Sm掺杂PMN-PZT压电陶瓷具有优异的综合电学性能,有望在换能器、传感器以及致动器等领域广泛应用。     

Outlook at the further development of the perovskite piezoelecthic ceramics

The remarkable electromechanical properties of the PZT-type piezoelectric ceramics approach presently to their saturation. Now it is necessary to research solid solutions which are not based on the Pb(Zr,Ti)O₃ system.     

The preparation and properties of PZT thin film by sputering method

The ferroelectric PZT thin films were prepared on Pt/Ti/SiO₂/Si substrate by RF sputtering method followed by the rapid thermal annealing. The preparation of the Pt and Ti thin films as bottom electrode, and their influences on the PZT thin films were studied in details. The substrate temperature during sputtering was room temperature; the rapid thermal annealing temperature was 500°C-750°C and the annealing time was 30-70s. The influences of different preparation parameters on the structure and electric properties were studied with X-ray diffraction technique and RT66A Standardized Ferroelectric Test System. The electric properties of the prepared PZT thin film was: P_a=39μc/cm₂, P_r = 9.3 μc/cm², E_c=28KV/mm, ε=300, p=10⁹ω⋅cm.     

Critical exponents of the dielectric constants in diffused-phase-transition crystals

The critical exponent γ in the relation between the dielectric constant and temperature (1/ε - 1/ε_m = C'^-1×(T - T_m)^γ) has been determined precisely for relaxor ferroelectrics Pb(Mg_1/3 Nb_2/3)O₃, Pb(Zn_1/3 Nb_2/3)O₃ and a related solid solution 0.88Pb(Zn_1/3 Nb_2/3)O₃-0.12PbTiO₃, as well as for normal ferroelectrics BaTiO₃ and K(Ta_0.55Nb_0.45)O₃. A high correlation of the γ value with the phase transition diffuseness has been found empirically. Moreover, this γ value is very close to another critical exponent γ^* which is defined in the relation between the dielectric constant and hydrostatic pressure (1/ε - 1/ε_m = C^*-1(p - p_m)^γε).     

Pulsed laser deposition of Sm modified PbTiO3 ferroelectric thin films

Sm modified PbTiO³ thin films have been prepared by pulsed laser deposition on Pt/TiO₂/SiO₂/(100)Si substrates. It has been found that the Sm concentration of the films remains close its concentration in the target, however, a Pb loss exists during the deposition process. To compensate for the Pb loss we used Pb rich targets and an oxygen pressure of 0.1 mbar. Films deposited at 530°C are crystalline and preferentially oriented with the [100] film direction perpendicular to the substrate surface. In comparison to bulk ceramics, the films have a tetragonal distortion lower than that expected from their Sm concentration. This is likely due to the influence of the substrate. The films prepared are ferroelectric with aP_r = 3.2 μC/cm².     

Microstructures and mechanical properties of 8Y-FSZ ceramics with BaTiO3 additive

The microstructure and mechanical properties of 8 mol% Y₂O₃ fully stabilized zirconia (8Y-FSZ) with BaTiO₃ additive were investigated. The introduction of BaTiO₃ additive would significantly increase the density and the grain size of 8Y-FSZ ceramics. XRD, Raman spectroscopy, and dielectric measurement were performed. A rhombohedral Ba(Ti_1−xZr_x)O₃ ferroelectric phase resulted in the composite with 5 mol% additive, while for those with higher additive content, the secondary phase changes to cubic Ba(Ti_1−xZr_x)O₃. The fracture toughness of the xBaTiO₃/(1−x)8Y-FSZ composites reached a maximum and then decreased with increasing the amount of additive. The highest value reached 6.1 MPa m^1/2 for 0.05BaTiO₃/0.95(8Y-FSZ) sintered at 1475 °C for 3 h, where the piezoelectric/ferroelectric secondary phase toughening played an important role. Moreover, the fracture toughness of the composites increased firstly and then decreased with increasing sintering temperature.     

Large hydrostatic piezoelectric constant and temperature dependence of the piezoelectric properties of Bi(NiTi)1/2O3: PbTiO3 ceramics

Large hydrostatic piezoelectric coefficient, d_h - 111 pC/N, for compositions in the system (1-x) Bi(NiTi)_1/2O₃: (x) PbTiO₃[BPNT] has been reported in this paper. Temperature dependencies of the dielectric, elastic, and piezoelectric properties of two compositions, x = 0.40 and x = 0.50, around the morphotropic phase boundary of Mn⁺² doped BPNT ceramics have been studied. Room temperature dielectric hysteresis loops with P_r = 37.86 μC/cm² and E_c = 25.75 kV/cm were observed for x = 0.40. Electromechanical coupling factors, k_p = 32.5%, k₃₁ = 19.7%, and k_t = 57.1% and piezoelectric constants, d₃₃ = 250 pC/N, d₃₁ = -67 pC/N, and d_h = 111 pC/N were measured in the BPNT-40 composition. The hydrophone figure of merit, d_hg_h ≈ 1055 × 10^-15 m²/N was calculated from these measurements.     

Temperature dependence of electrical and electromechanical properties of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thin films

The electrical and electromechanical properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PNN–PZT, PMN/PNN/PZT = 20/10/70) on Pt/Ti/SiO₂/Si substrates by chemical solution deposition was investigated. The PMN–PNN–PZT films annealed at 650 °C exhibited slim polarization hysteresis curves and a high dielectric constant of 2100 at room temperature. A broad dielectric maximum at approximately 140–170 °C was observed. The field-induced displacement was measured by scanning probe microscopy, the bipolar displacement was not hysteretic, and the effective piezoelectric coefficient (d₃₃) was 66 × 10⁻¹² m/V. The effective d₃₃ decreased with temperature, but the value at 100 °C remained 45 × 10⁻¹² m/V.     

Phase transition in Sol-Gel processed barium titanate ceramics

Ferroelectric barium titanate (BaTiO₃) ceramics have been prepared from barium acetate [Ba(CH₃COO)₂] and titanium isopropoxide [Ti(CH₃)₂CHO)₄] precursors by sol-gel technique The as-grown powder was found to be amorphous which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The ceramics showed well saturated polarization-field (P-E) hysteresis loops at room temperature. The values of spontaneous polarization(P_s), remanent polarization (P_r) and coercive field (E_c) of the ceramics were found to be19.0, 12.66μC-cm^-2 and 30KVcm^-1 respectively. The room temperature dielectric constant (ε) and loss tangent (tanδ) of the ceramics were found to be 1135 and 0.012 respectively. The dielectric constant and tanδ showed anomaly peaks at 125°C showing ferroelectric to paraelectric phase transition. The polarization parameters also vanish at 125°C confirming the phase transition.     

Microwave dielectric properties and co-firing with copper of (Bi1−xCux)(Nb1−xWx)O4 ceramics

Effect of substitution of CuO and WO₃ on the microwave dielectric properties of BiNbO₄ ceramics and the co-firing between ceramics and copper electrode were investigated. The (Bi_1−xCu_x)(Nb_1−xW_x)O₄ (x = 0.005, 0.01, 0.015, 0.02) composition can be densified between 900 and 990 °C. The microwave dielectric constants lie between 36 and 45 and the pores in ceramics were found to be the main influence. The Q values changes between 1400 and 2900 with different x values and sintering temperatures while Q_f values lie between 6000 and 16,000 GHz. The microwave dielectric losses, mainly affected by the grain size, pores, and the secondary phase, are discussed. The (Bi_1−xCu_x)(Nb_1−xW_x)O₄ ceramics and copper electrode was co-fired under N₂ atmosphere at 850 °C and the EDS analysis showed no reaction between the dielectrics and copper electrodes. This result presented the (Bi_1−xCu_x)(Nb_1−xW_x)O₄ dielectric materials to be good candidates for LTCC applications with copper electrode.     

Defect formation and mechanical stability of perovskites based on LaCrO3 for solid oxide fuel cells (SOFC)

Perovskites on the basis of LaCrO₃ are of interest as ceramic interconnect materials for the development of solid oxide fuel cells (SOFCs). The interconnects are exposed to oxidising and reducing atmospheres under operating conditions. Oxygen vacancy formation was determined as a function of oxygen partial pressure between 1 and 10⁻²² bar at temperatures between 900 and 1100 °C. Different perovskite compositions made of (La,Ca/Sr)CrO_3−δ, La(Cr,Mg)O_3−δ, La(Cr,Mg/Cu/Co,Al)O_3−δ, and (La,Ca)(Cr,Al)O_3−δ were investigated. Defect models were evaluated to describe the oxygen vacancy formation and the respective thermodynamic data were determined. The results are used to explain existing literature data on the isothermal expansion of LaCrO₃ based perovskites under reducing conditions. Complementary mechanical measurements with selected perovskite compositions revealed that lower oxygen partial pressure causes higher stiffness, strength and fracture toughness. The change in properties is discussed in terms of the observed ferroelastic domains and the interaction of the domain wall motion with the oxygen vacancies.     

Structure stabilization and dielectric properties of pzn ferroelectric ceramics

Structure stabilization and dielectric properties of Pb (Zn_1/3 Nb_2/3)O₃ -PbTiO₃ -BaTio₃ (PZN-PT-BT) ferroelectric ceramics have been carefully studied. Around morphotropic phase boundary (MPB) of PZN-PT system, heterovalant substitution of K⁺ for Pb²⁺ stabilizes the pesrovskite Structure, while substitution of La³⁺ for Pb²⁺ goes toward the other end. Nonstoichiometry addition of excess ZnO or BaO can also suppress the formation of pyrochlore phase.     

Piezoelectric properties of Pb(Mn1/3Nb2/3)O3–PbZrO3–PbTiO3 ceramics with sintering aid of 2CaO–Fe2O3 compound

Since the electromechanical devices move towards enhanced power density, high mechanical quality factor (Q_m) and electromechanical coupling factor (k_p) are commonly needed for the high powered piezoelectric transformer with Q_m≥2000 and k_p=0.60. Although Pb(Mn_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Q_m and k_p are needed. Addition of 2CaO–Fe₂O₃ has been proved to have many beneficial effects on Pb(Zr,Ti)O₃ ceramics. Therefore, 2CaO–Fe₂O₃ is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn_1/3Nb_2/3)O₃–0.468PbZrO₃–0.462PbTiO₃ (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe₂O₃ additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Q_m has the maximum 2150 with 0.3 wt.% 2CaO–Fe₂O₃ addition. The k_p more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe₂O₃ can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe₂O₃ at both sintering temperatures.