Influence of the sintering conditions on the physical proprieties of the ceramic PFN multiferroics

An influence of compacting conditions on applied properties of the multiferroic PbFe_1/2Nb_1/2O₃ (PFN) ceramics synthesized by the columbite method and powder calcination technique is presented in this work. The obtained specimens were subjected to X-ray and chemical composition homogeneity analyses, magnetic tests, electric direct current conductivity and electromechanical tests. Differences in the degree of diffuseness, densities and a grain size were observed depending on the sintering method. The dielectric and magnetic parameters as a function of temperature were measured. The tests confirmed that PFN powder compacting by a hot uniaxial pressing method had an advantageous influence on the crystalline structure ordering and the ceramics microstructure, what improves the applied properties of the material.     

Piezoelectric properties and dielectric behavior of Bi1/2Na1/2[Ti1−x (Sb1/2Nb1/2) x ]O3 lead-free piezoelectric ceramics

New lead-free piezoelectric ceramics of ABO₃ perovskite type, Bi_1/2Na_1/2[Ti_1−x (Sb_1/2Nb_1/2) _x ]O₃, were synthesized by conventional solid state reaction. The effect of the replacement of complex ions of (Sb_1/2Nb_1/2)⁴⁺ in the B cationic site on structural and electrical properties was investigated. The XRD analysis showed that all samples exhibited a single phase of perovskite structure. Piezoelectric and dielectric measurement revealed that the substitution of (Sb_1/2Nb_1/2)⁴⁺ ions lead to an increase in piezoelectric constant(d ₃₃), electromechanical coupling factor(k _t), relative dielectric constant(ɛ _r),and loss tangent (tanδ), while excess of (Nb_1/2Sb_1/2)⁴⁺ ions results in a decrease in d ₃₃, k _t, ɛ _r, but an increase in tanδ. Temperature dependence of dielectric constant ɛ _r measurement indicated these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant increased sharply attributed to the superparaelectric clusters after (Sb_1/2Nb_1/2)⁴⁺ ions substitution.     

Ferroelectricity in Aurivillius-Type Structure Ceramics with n = 2 and (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 Composition

Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization. Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials. In this work, ceramics with nominal composition (SrBi₂Nb₂O₉)_0.35(Bi₃TiNbO₉)_0.65 (T_C∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity, dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated ferroelectric hysteresis loops at 250^∘C have been obtained, with values of P_r = 21.4 μ C/cm² and E_c = 70.4 kV/cm.     

Substituent Effects in 0.65Pb(Mg1/3Nb2/3O30.35PbTiO3 Piezoelectric Ceramics

Pb(Mg_1/3Nb_2/3O₃–-PbTiO₃ (PMN-PT) ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers and actuators due to their high dielectric constants and electromechanical coupling factors. However, their dielectrical and mechanical losses are too high for high-power applications. In this paper, the dielectric and electromechanical properties of piezoelectric PMN-PT ceramics were investigated in specimens containing various A-site and B-site substituents with the goal of developing lower loss materials for wider applications. Emphasis was placed on various transition metal cation substituents of both lower and higher valences. Mn substituent was found to be the most promising substituent investigated for developing high power low loss piezoelectric PMN-PT ceramics.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias

Recently, one type of thermal-type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature T_c for stable responsivity to temperature. Electric field induced-type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg_1/3Nb_2/3)O₃ (PMN) and Pb(Sc_1/2Ta_1/2)O₃ (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor. This paper describes the sensor properties of electric field induced-type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high-response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced-type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.     

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbSc_1/2Nb_1/2O₃ (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (～50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ～ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg_1/3Nb_2/3O₃ to PbSc_1/2Nb_1/2O₃ related type.     

Processing and Electrical Properties of 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 Ceramics

Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ ceramics at the morphotropic phase boundary (50:50) were sintered by conventional and reactive methods to 95% theoretical density and grain sizes <10 m. Excess PbO, added to enhance the densification, resulted in PbO-based non-ferroelectric phases that degraded the electrical properties. Volatilization of excess PbO by annealing the samples after sintering resulted in dense, perovskite samples and excellent electrical properties. The best electrical properties, obtained via reactive sintering, were a remanent polarization, P _r, of 0.36 C/m², a maximum dielectric constant of 31,000 (at the T _c = 371°C and 1 kHz), a piezoelectric charge coefficient, d ₃₃, of 508 pC/N, and an electromechanical coupling coefficient, k ₃₃, of 0.61.     

Enhanced electrochemical and thermal properties of Sm2O3 coated Li[Li1/6Mn1/2Ni1/6Co1/6]O2 for Li-ion batteries

For EV vehicles of the future, a lithium ion battery with highly enhanced electrochemical and thermal properties has been widely investigated. Here we introduce Sm₂O₃ as a new surface coating source for the cathode material of Li-ion batteries and explore the effects of the Sm₂O₃ coating using XRD, EIS, and DSC measurements. The cathode material used is Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. The XRD and TEM results indicate that the Sm₂O₃ is coated on the surface of the cathode material without changing the layered structure of the core Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. With the Sm₂O₃ coating, the cycling performance during 50 cycles using 6 C rate, as well as 1 C rate, is highly improved, five times better. The EIS results show that film resistance and the charge transfer resistance decrease in comparison with the pristine Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. Furthermore, the DSC results show a highly enhanced thermal property. We highly recommend the Sm₂O₃ coating for Li-ion batteries for various applications.     

Fabrication and operation limit of lead-free PTCR ceramics using BaTiO3–(Bi1/2Na1/2)TiO3 system

The electric properties of BaTiO₃–(Bi_1/2Na_1/2)TiO₃ (BT–BNT) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130°C. For determining the maximum switching temperature T _s, the phase diagram of BT–BNT binary system was clarified. Two semiconductorization processes and their electric properties are described. The lanthanum(La)-doped BBNT ceramics sintered in air still showed dielectric behaviors, but the niobium(Nb)-doped ones had a low resistivity at room temperature, ρ _RT, on the order of 10³ Ωcm and showed a PTC behavior. Sintering under a low O₂ atmosphere produces BT–BNT ceramics with less than 10² Ωcm compared to those prepared in air. Our current research produced the BBNT ceramics with T _s values around 210°C by increasing the (Bi_1/2Na_1/2) content in the ceramics.     

Piezoelectric and dielectric characteristics of low temperature sintering Pb(Ni1/3Nb2/3)O3-Pb(Mn1/3Nb2/3)O3-Pb(Zr1/2Ti1/2)O3 ceramics for multilayer piezoelectric actuator

In this study, in order to develop the composition ceramics for multilayer piezoelectric actuator, PNN substituted PMN-PZT ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated. With the increase of the amount of PNN substitution, dielectric constant (εr), electromechanical coupling factor (k _p), and piezoelectric constant (d ₃₃) of specimens showed the maximum value at each sintering temperature, and crystal structure changed from tetragonal to rhombohedral. At the sintering temperature of 950^∘C, the density, εr, k _p, d ₃₃, Q_m and Tc of 12 mol% PNN substituted PMN-PNN-PZT composition ceramics showed the optimal values of 7.79 g/cm³, 1160, 0.599, 419pC/N, 894 and 332^∘C, respectively, for low loss multilayer piezoelectric actuator application.     

Defect chemistry and transport properties of Pb(Zr1/2Ti1/2)O3

Abstract

In order to gain insight into the degradation mechanisms associated with ferroelectric thin films, such as fatigue and imprint, an understanding of the defect chemistry and transport properties of the material is needed. In this study several complimentary techniques have been used to either measure or calculate indirectly the various thermodynamic parameters governing defect formation and transport in Pb(Zr_1/2Ti_1/2)O₃, (PZT). By combining the results of DC equilibrium conductivity, thermoelectric power and the sealed cell techniques, “constant composition oxygen activity” and “constant composition conductivity,” values for the oxidation enthalpy (ΔH_ox), hole trapping energy (E _A) and the enthalpy of motion for holes (ΔE _A) have been determined to be ?0.49 eV, ≤0.9 eV and ≥0.1 eV, respectively. From these results, it is apparent that PZT is an oxygen excess p-type semiconductor in the experimental regime of 500°–700°C and P(O₂) ≥ 10^?4 atm. Furthermore, the results indicate that there is a significant concentration of trapped holes at high temperatures and hole conduction appears to be an activated process (i.e. small polaron conduction).     

Piezoelectric ceramics of (Bi1/2Na1/2)TiO3-PbTiO3-BaTiO3 system

Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi_1/2Na_1/2)TiO₃(BNT)-based solid solution, that is, (Bi_1/2Na_1/2)(_1-x)(Pb_a Ba_b)_xTiO₃(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(F_a-tetragonal (F_β) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi_1/2Na_1/2)TiO₃[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε₃₃Tε₀, and a high electromechanical coupling factor k₃₃, along with a high mechanical strength.     

Mechanical and electric fatigue of PZT(53/47) films on metallic substrates

Abstract

We have investigated the fatigue of electromechanical and dielectric properties of sol-gel derived PZT(53/47) thin films deposited on metallic substrates by means of electric and mechanical cycling. For the mechanical cycling a two point bending method was used to apply transversal stress to the samples. During mechanical cycling the piezoelectric coefficient d₃₁ remained constant up to about 10⁵ cycles, for a higher number of cycles a strong decrease was observed. During electric cycling no significant changes in the ferroelectric and electromechanical hysteresis loops could be found up to about 3×10⁵ cycles. Above this number the coercive field increases, the maximum strain and the remanent polarization decrease.

Obviously each electric cycling of the investigated films is accompanied by a mechanical cycling. It is assumed, that microcracks induced by mechanical stress are the main reason for the deterioration of the physical properties films during electric and mechanical cycling both.     

Surface acoustic wave properties in 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001]c

Surface acoustic wave propagation in a 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ multidomain single crystal poled along [001]_c has been analyzed theoretically using Christoffel wave equations. From the measured experimental data, the orientational dependence of surface acoustic wave phase velocities, electromechanical coupling coefficients and power flow angles was calculated. The results showed that surface acoustic wave propagations of 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ are poor than 0.93Pb(Zn_1/3Nb_2/3)O₃-0.07PbTiO₃ crystal slightly. However, the 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ single crystals have higher rhombohedral-tetragonal phase transition temperature and much stabler electromechanical properties. This may expand applications range of SAW devices.     

Piezoelectric properties of the Pb(Sc1/2Nb1/2) O3-Pb(Mg1/3Nb2/3) O3-PbTiO3 ternary ceramic materials near the morphotropic phase boundary

Abstract

The physical and electrical properties of xPb(Sc_1/2Nb_1/2)O₃-yPb(Mg_1/3Nb_2/3)O₃-zPbTiO₃(PSMNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows on almost linear region between the PSMNT 58/00/42 and PSMNT 00/68/32 MPB compositions of the binary systems. The maximum piezoelectric constant, d ₃₃ = 680 pC/N, were found at PSMNT 29/33/38, where ε^T ₃₃/ε₀ = 3,800, and electromechanical coupling factors, (k _p = 70%, k₃₁ = 43%, and k ₃₃ = 76%) and T _c = 207°C were obtained. The maximum electromechanical coupling factors, (k _p = 72%, k ₃₁ = 45%, and k ₃₃ = 77%) were found at PSMNT 29/34/37, where ε^T ₃₃/ε₀ = 3,000, d ₃₃ = 640 pC/N, and T _c = 205°C were obtained. These values are better than those of PZT.     

Fabrication and properties of 1-3-2 multi-element piezoelectric composite

A design method is presented for 1-3-2 type multi-element piezoelectric composite so as to provide basis for the development and study of transducer and transducer array. The composite samples have been fabricated by a twice dice-filling process from lead zirconate titanate (PZT-4), epoxy resin and silicone, the properties of the composites have been measured and investigated physically. The results show that the piezoelectric, dielectric and electromechanical coupling properties of the composite exhibit a good consistency, while it has a high thickness electromechanical coupling factor K _t and a wide bandwidth of pulse-echo signal. The impedance plot of every element indicates good behavior that all elements show excellent frequency consistency, and on the other hand the chance of coupling of lateral resonance and thickness resonance is very small, and with a clear thickness resonance mode at around 100?kHz. Silicon has extremely decoupling properties which can efficiently block the transmission of the acoustic vibrations and eliminate coupling effect among elements. And the farther the distance between the incentive element and receiving element is, the smaller the response signal become, while the response signal decay rate exhibits the trend of increase, the largest up to 95%.     

Fabrication and electrical properties of textured Na1/2Bi1/2TiO3-BaTiO3 ceramics by reactive-templated grain growth

The <001> fiber-textured Na_1/2 Bi_1/2TiO₃-BaTiO₃ (6 mol% BaTiO₃) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi₄Ti₃O₁₄ (BiT) particles prepared by a molten salt method as templates. The effects of sintering conditions on texture development and microstructure evolvement were both studied, and the mechanisms of grain orientation and densification were discussed. High Lotgering factor (≥96%) and high density (≥96% theoretic density) textured Na_1/2 Bi_1/2TiO₃-6BaTiO₃ ceramics were prepared by using the max templates concentration supplying 100% Bi in the final product, and sintering at 1200 °C for 10 h. The NBT-6BT obtained exhibited good piezoelectric performance with piezoelectric coefficient d ₃₃ ?=?241pC/N, and electromechanical coupling factor k _p ?=?41.2%, k _t ?=?66.5% at room temperature.     

Electrical conductivity of the Al-stabilized La<Subscript>2/3</Subscript>TiO<Subscript>3</Subscript>

A-site deficient lanthanum titanate (La_2/3TiO₃) materials with perovskite structure are attractive due to their electrical applications such as ion conductors and dielectrics. However, its stability at room temperature in air is obtained only if Na or Li etc. is incorporated into La site or Al into Ti site. In this study, the electrical conductivities of La_0.683(Ti_0.95Al_0.05)O₃ have been measured in oxygen partial pressure (Po₂) between 1 and 10⁻¹⁸ atm at 1000~1400°C. The electrical conductivity exhibited −1/4, −1/6 and −1/5 dependence (log σ ∝ log , n = −1/4, −1/6, −1/5) depending upon temperature and Po₂. The defect model explaining the observation was proposed and discussed. The chemical diffusion coefficient was estimated from the electrical conductivity relaxation.     

Pulsed Laser Deposited Ba(Mg1/3Ta2/3)O3 Microwave Dielectric Thin Films

Ba(Mg_1/3Ta_2/3)O₃ (BMT) microwave dielectric thin films were successfully synthesized by a modified pulsed laser deposition (PLD) process, which includes low temperature (200°C) deposition and high temperature (>500°C) annealing. Crystalline structured BMT thin films were obtained when the PLD-deposited films were post-annealed at a temperature higher than 500°C in oxygen atmosphere. The characteristics of BMT thin film, including crystallinity, grain size, film roughness, and dielectric properties were improved with annealing temperature, achieving dielectric constant K = 23.5 and dissipation factor tan δ = 0.015 (at 1 MHz) for the 800°C-annealed films.