Effect of Microstructure on Ferroelectric and Piezoelectric Properties of A-Site and B-Site Modified PLZT

Ba modified (Pb,La,Ag)(Zr,Ti)O₃ ceramics synthesized by conventional mixed-oxide method with chemical formula [Pb_{0.983 - z}La_0.012Ag_0.005Ba_z] [(Zr_0.52Ti_0.48)_0.99825]O₃ were investigated for ferroelectric and piezoelectric properties. XRD studies indicate that increment of Ba concentration resulted in strong tetragonality in the ceramics. Grain growth (3.08 μ m) inhibited and apparent density (7.54 gm/cm³) enhanced up to 1.5 mole% Ba respectively. As Ba content increased dielectric properties showed maximum values (ε_RT = 2347, ε_Tc = 23449) while T_c constantly decreased. The remanent (P_r = 34.72 μ C/cm²) and spontaneous polarization (P_s = 41.84 μ C/cm²) were optimum in 1 mole% Ba respectively while E_c showed increasing trend throughout the series. Piezoelectric properties attained maximum values of d₃₃ = 438 pC/N in 1.5 mole% Ba while k_p = 0.533 and k_t = 0.412 in 1 mole% Ba doped (Pb,La,Ag)(Zr,Ti)O₃ ceramics respectively.     

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.     

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.     

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.     

Ferroelectricity in AgNbl-xTaxO3 solid solutions

Existence of the ferroelectric phase in AgNb_l-xTa_xO₃ solid solutions was confirmed. Temperature of the ferroelectric phase transition decreases from 348K for AgNbO₃ to 140K for AgNb_0.4Ta_0.6O₃ with increasing Ta concentration. Investigations of spontaneous polarization P_s, total pyroelectric coefficient p_t and dielectric permittivity were carried out for ceramic samples (0 ≤ X ≤ 0.6). Values of P_s, p_t and ε_max increase with increaseing Ta concentration. Values of P_s are of the order of 0.1 μC/cm².     

Ferroelasticity and ferroelectricity in betaine arsenate

Single crystals of betaine arsenate, an addition compound of the amino acid betaine with H₃AsO₄, were investigated by dielectric, optical, caloric, and X-ray methods. At room temperature betaine arsenate is ferroelastic with two different monoclinic domains. This state seems to disappear at 411 K. Below T_c = 119 K the ferroelastic domains show a ferroelectric behaviour with a spontaneous polarization P_s = 2μC/cm² at T = T_c - 35 deg.     

Complex piezoelectric, elastic, and dielectric coefficients of La-DOPED 0.93 Pb(Mg1/3Nb2/3)O3:0.07 PbTiO3 under DC bias

Complex material parameters (piezoelectric coefficient d₃₁, elastic s₁₁^E, and the dielectric constant K₃₃) of the relaxor ferroelectric ceramic (1-x) Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃(x =.07) with 1% La (lanthanum) were measured as a function of bias field using a bar resonator. The values of the dielectric and piezoelectric phase angles are found to be comparable (i.e., around 0.04 for a d.c. bias field of 2.5 kV/cm), while the elastic phase angle is an order of magnitude smaller (0.001 for the same d.c. bias). For comparison of complex material parameters found from bar resonators, a sample in the form of a small disk is used to measure Poisson's ratio as well as the real components of the piezoelectric and elastic coefficients as a function of bias field.     

Effects of Excess Bismuth Content in Precursor Solutions on Ferroelectric Properties of BiFeO3 Thin Films Prepared by a Chemical Solution Deposition

Cr-substituted BiFeO₃ (BFCr) thin films prepared from precursor solutions with stoichiometric composition and various excess Bi contents ranged from 5 to 20 mol% were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a chemical solution deposition method, and the effects of excess Bi content in precursor solutions on the ferroelectric properties of the as-deposited BFCr thin films were studied. It was found that the BFCr thin film prepared from precursor solution with excess Bi content of 5 mol% exhibited the best dielectric constant-frequency and polarization-electric field characteristics. In detail, its dielectric constant is 158 at frequency of 100 kHz and remnant polarization (P_r) value is 49 μ C/cm² at electric field of 600 kV/cm.     

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.     

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.     

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).     

A new tantalum sulfur compound as electrode material for non-aqueous alkali metal batteries

Polycrystalline (PbS)_1.14(TaS₂)₂, a misfit layer sulfide, was used as cathodic material for lithium secondary battery. One molar LiClO₄ in propylene carbonate (PC) was used as electrolyte. The cell could be galvanostatic discharged down to x = 4.6 [Li_x(PbS)_1.14(TaS₂)₂] when the current density was 65 μA cm⁻² and the cell was cycled more than 100 times between 3.5 and 1.5 V at a current density of 260 μA cm⁻². Lattice expansion increased linearly with lithium content and was less than that reported for the Li/TaS₂ system. Chemical diffusion coefficients were determined by a modified version of the galvanostatic intermittent titration technique and they were fairly constant in the composition range 0.2 < x < 1, and an average value of 8.1 × 10⁻¹¹ cm² s⁻¹ was calculated. Sodium intercalation was also accomplished, but the uptake of this ion resulting in a significant lattice expansion compared with that observed for lithium ions. Moreover, a similar dependence of the sodium chemical diffusion coefficient on the composition was observed with an average value of 1.4 × 10⁻¹⁰ cm² s⁻¹, somewhat higher than that of lithium ion. We believe that differences in lattice expansion may be responsible for the differences found in the chemical diffusivity values.     

Influences of Cr Doping on the Electrical Properties in BiFeO3 Thin Films

Cr-doped BiFeO₃ (BFO) thin films were deposited on Pt(200)/TiO₂/SiO₂/Si(100) substrates by a chemical solution deposition method. The dielectric constant and dissipation factor of the BFO thin films decrease from 165 and 0.054 (undoped) to 100 and 0.02 (3 mol% Cr-doped) at a frequency of 10 kHz as the Cr content increases. The leakage current and ferroelectric properties were improved significantly by means of Cr doping. The leakage current density of 4.1×10^-6 A/cm² for the 3 mol% Cr-doped BFO thin film is about four orders of magnitude lower than that of undoped BFO thin film at an external electric field of 100 kV/cm. The 3 mol% Cr-doped BFO thin film exhibited a well-saturated hysteresis loop with a large remanent polarization (P_r) of 61 μC/cm² at room temperature. The reason for the improved leakage current and ferroelectric properties in Cr-doped BFO thin films can be attributed to the reduced oxygen vacancies in the films by Cr doping.

Communicated by Dr. George W. Taylor     

Dielectric, pyroelectric and piezoelectric properties of calcium-modified lead magnesium tantalate-lead titanate ceramics

Dielectric, pyroelectric and piezoelectric properties of relaxor ferroelectrics in solid solution, formulated 0.65(Pb_1-xCa_x)(Mg_1/3Ta_2/3)O₃-0.35PbTiO₃, have been investigated. Complete single-phase perovskite with high density was obtained with all samples fired at 1250°C. The Curie temperature and pyroelectric peak temperature decrease almost linearly as the amount of Ca in the compositions increases. The transition temperature of the solid solutions can easily be controlled by Ca additions in the PMT-PT. Dielectric, pyroelectric and piezoelectric constants achieved maximum values for x=0.02. Compositions near 0.65PMT-0.35PT-0.12Ca have been identified to have high dielectric constants(∼ 15000) and low dissipation factors(∼ 0.015) near room temperature.     

Soft piezoelectric (1-x)Pb(Sc1/22Ta1/2)O3-(x)PbTiO3 ceramics with high coupling factors and low QM

The piezoelectric behavior of materials from the (1-x)Pb(Sc_1/22Ta_1/2)O₃-(x)PbTiO₃ solid solution system has been investigated. The [x = 0.45] composition in particular has exhibited an outstanding piezoelectric response [d₃₃ = 650 (pC/N). k_t = 0.5, k_p = 0.61. k₃₃ = 0.73] and a low mechanical quality factor [Q_M = 30]. These features make it a promising candidate for a variety of piezoelectric sensor applications. The difficulties involved in effectively poling a bar sample and a means to avoid these problems are also addressed.     

New Preparation Method of Low-Temperature-Sinterable Perovskite 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Powder and Its Dielectric Properties

A relaxor ferroelectric material, 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (0.9PMN-0.1PT) with a pyrochlore-free phase, was prepared by using one-step calcination in the present study. The 0.9PMN-0.1PT powder with the pure perovskite phase was prepared successfully from a mixture of the PMN precursor and the crystalline PT by heating for 2 h at temperatures greaterthan equal to750°C. The PMN precursor was synthesized by adding an aqueous Mg(NO₃)₂ solution, rather than MgO, to the alcoholic slurry of PbO and Nb₂O₅. The 0.9PMN-0.1PT powder sintered to >96% relative density via heat treatment for 2 h at temperatures of 900°-1200°C. The highest room-temperature dielectric constant (epsilon_rt) was 24700 at 1 kHz for the samples that were sintered at 1100°C; however, the samples that were sintered at 900°C still had epsilon_rt values of 22600 at 1 kHz.     

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.     

Thickness effects on structures and electrical properties of lead zirconate titanate thick films

PbZr_0.52Ti_0.48O₃ thick films with thickness of 1–6 μm have been prepared by a polymer-assisted MOD process. The polymer, poly(vinyl acetate) (PVAc) was introduced into PZT precursor solutions. The grain size increased from 30 nm to 100 nm with an increase of the additive amount of PVAc. Meanwhile, the grains grew larger (in a range of 100–500 nm) and the surface of the films became rougher with increasing film thickness. This promotes the structural relaxation and prevents cracking formation. The critical thickness at which the film begins to crack increases significantly. The dielectric constant and remanent polarization (P_r) increased from 1070 to 1490 and from 36.1 μC/cm² to 52.4 μC/cm², respectively, and the coercive field (E_c) decreased from 57.3 kV/cm to 41.3 kV/cm as the film thickness increased from 0.95 μm to 6.02 μm. PZT thick films prepared in this study are promising materials for MEMS applications.     

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.     

Synthesis and properties of Bi0.5(Na1−x−yKxAgy)0.5TiO3 lead-free piezoelectric ceramics

Bi_0.5(Na_1−x−yK_xAg_y)_0.5TiO₃ piezoelectric ceramics were prepared by conventional ceramic processes. X-ray diffraction patterns show a pure perovskite structure, indicating that the K⁺ and Ag⁺ ions substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃. The temperature dependence of the dielectric constant and dissipation factor shows all ceramics to experience two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The transition temperature from ferroelectric to anti-ferroelectric and the temperature at which the dielectric constant reaches its maximum value decrease with the increase of K⁺ amount. At room temperature, the ceramics containing 17.5–20 mol% K⁺ and 2 mol% Ag⁺ exhibit high piezoelectric constant (d₃₃ = 180 pC/N) and high electromechanical coupling factor (k_p = 35%).