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Ni-decorated h-BN powders are fabricated with ChCl-EG as additive via electroless plating in the paper. As comparison, the different additive concentration of choline chloride-ethylene glycol (ChCl-EG) ionic liquid (0 g l−1, 30 g l−1, 60 g l−1, 90 g l−1) is presented. The effects of ChCl-EG concentration are studied, including the surface morphologies, phase analysis of Ni-decorated h-BN powders and the residual Ni2+ concentration is measured in electroless plating bath. It is demonstrated that the deposition phenomena of nickel particles on h-BN surface is changed with the addition of ChCl-EG. When the concentration of ChCl-EG is 30 g l−1, the Ni particles on h-BN surface are in dispersed and spheroid state with the average size of 10–1000 nm. It can be found that 30 g l−1 ChCl-EG is conducive to the arise of deposition phenomena, which is the formation of the single nickel particle on h-BN surface. Besides, more Ni particles are deposited on h-BN surface with the increase of nickel plating times, which is characterized with scanning electron microscope and transmission electron microscope. Furthermore, the deposition phenomenon and growth mechanism are proposed without and with ChCl-EG as additive to further elaborate the formation of Ni particles on h-BN surface.

We report on temperature dependence of local electromechanical properties of lead-free (K,Na)NbO3-based ceramics that macroscopically manifests a large temperature-insensitive strain. Piezoresponse force microscopy reveals the particular role of the orthorhombic-tetragonal phase transition, where a reconstruction of the domain structure occurs and local piezoelectric response shows a peak value. A good quantitative agreement between temperature dependences of the local and previously reported macroscopic small-signal piezoelectric coefficients is observed. An influence of the polymorphic phase transition on polarization switching kinetics was revealed. [ABSTRACT FROM AUTHOR]

Microscale 1-3-type-like magnetoelectric (ME) composites with ferromagnetic microstrips laterally embedded in a piezoelectric ceramic substrate were fabricated by a dice-and-insert method. Mechanically sliced microstrips of Li/Ta-modified (K,Na)NbO3 lead-free ceramics and CoFe2O4 ceramics were used as the piezoelectric and piezomagnetic phases, respectively, which were inserted into each other and bonded together by epoxy. The ME properties of such 1-3-type-like composites with piezoelectric substrates were verified. The maximum ME coefficient was found to vary with the strip size, substrate thickness, and thickness of epoxy bonding layers. A maximum value of 48 mV/(cm·Oe) was achieved. In addition, a special anisotropy was obtained in the present lateral 1-3 type ceramic composites and made it have potential applications in detecting magnetic field directions. [ABSTRACT FROM AUTHOR]

Phase structure, dielectric, ferroelectric and piezoelectric properties of dense 0.95(NaKLi)(NbTa)O-0.05CaZrO lead-free ceramics prepared by spark plasma sintering (SPS) are reported. Compared with normal sintering, SPS yields a pseudocubic perovskite phase structure with a reduced c/a ratio, enhanced mechanical property and a lower Curie temperature. Large electric-field-induced strain of 0.135 % can be achieved at 4 kV/mm, accompanied with reduced ferroelectricity as evidenced by the slim polarization P( E) hysteresis loops and 'sprout'-shaped bipolar strain curves. The piezoelectric strain is temperature insensitive in the range from room temperature to about 100 °C, featuring the current material promising potential for practical applications. [ABSTRACT FROM AUTHOR]

( Ba1− x Ca x)( Ti0.92 Sn0.08) O3 ( x = 0.00-0.06 mol) ceramics with a high relative density over 96% were prepared by a conventional sintering method at 1480°C. At room temperature, a polymorphic phase transition from orthorhombic phase to tetragonal phase was confirmed by the XRD patterns in the composition range of 0.04 ≤ x ≤ 0.06. A high piezoelectric coefficient d33 up to 568 pC/N was obtained at x = 0.05 mol, which is higher than the other component of ( Ba, Ca)( Ti, Sn) O3 system. At the same time, the corresponding planar electromechanical coupling factor kp, converse piezoelectric coefficient dS/ dE, and dielectric constant εr reach 47.7%, 1013 pm/V, and 23000, respectively. These results indicate that the ( Ba, Ca)( Ti, Sn) O3 ceramics are a promising candidate to replace for the lead-based piezoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract: XRD and Raman scattering experiments revealed an interesting finding that phase structure changed from orthorhombic to tetragonal symmetry when pulverizing (Li,Ta)-doped (K,Na)NbO3 lead-free piezoelectric ceramics (sintered body) to powder. Both orthorhombic and tetragonal phases coexist in the Li0.05(Na0.51K0.49)0.95Nb0.80Ta0.20O3.00 (LKNNT) sintered bulk sample at room temperature, but almost only the tetragonal phase is observed in the ground powder. In addition, annealing experiment enhanced the formation of tetragonal phase and improved the temperature stability of piezoelectricity. It is revealed that the internal stress existing in the LKNNT ceramics favors the formation of orthorhombic phase, which transfers to tetragonal phase when the stress was released. [Copyright &y& Elsevier]

Silver antimonate (AgSbO) is a potential high-temperature thermoelectric oxide with a low thermal conductivity, but it is difficult to fabricate dense bulk material with high phase purity. Well-dispersed AgSbO nanopowder with an average diameter of 50 nm was synthesized by an ion-exchange process in this study, the sintering density of which was apparently enhanced. Nearly single-phase AgSbO ceramic samples with a relative density close to 90% were obtained when sintered at a relatively low temperature (1273 K). The electrical conductivity of AgSbO increased greatly with increasing sintering temperature, probably because of defects originating from the compositional deviation caused by sintering, in addition to increased density. This study also confirmed that AgSbO had a low thermal conductivity, from 1.1 W m K at room temperature to 0.8 W m K at 673 K. [ABSTRACT FROM AUTHOR]

With the assistance of excess Na2O additives, LiNbO3-doped (K, Na)NbO3 lead-free piezoceramics were successfully prepared by conventional sintering at a temperature as low as 950°C. Shrinkage curve measurement and micrograph observation elucidate that the nature of the densification behavior at 950°C is liquid phase sintering, during which the liquid phase penetrated between initial small particles and large quadrate grains of 20–40 μm formed in the solution–precipitation process. Although the density and grain size show inappreciable changes during the final stage of the coalescence process, the piezoelectric properties of the sintered samples are greatly influenced by the soaking time, depending on the optimization of which the piezoelectric constant d33 and the planar mode of the electromechanical coupling factor kp reached 280 pC/N and 48.3%, respectively. The present study revealed that good piezoelectric properties can be obtained in the Li-doped KNN ceramics even by normal sintering at a reduced temperature (950°C). [ABSTRACT FROM AUTHOR]

Crystallographic structure, phase transition and electrical properties of lead-free (Na0.535K0.485)1− xLi x(Nb0.942Ta0.058)O3 ( x=0.042–0.098) (NKL xNT) piezoelectric ceramics were investigated. The experimental results show that both Li content and sintering temperature strongly affect the orthorhombic–tetragonal polymorphic phase boundary (PPB), which results in remarkable differences of the piezoelectric property and its temperature stability in the NKL xNT ceramics. Chemical analysis indicates that sodium volatilizes more seriously than potassium and lithium with increasing sintering temperature. Due to the comprehensively optimized effects of Li content and sintering temperature, an enhanced piezoelectric constant d33 (276 pC/N) was obtained at room temperature in the ceramics with x=0.074 sintered at 1000°C. In the same composition, a further high d33 up to 354 pC/N was obtained at 43°C, which is close to its To−t temperature. Furthermore, better temperature stability can be obtained when x=0.082 sintered at 1000°C, whose piezoelectric constant d33 (236 pC/N) keeps almost constant from room temperature to 100°C. Such a temperature-independent piezoelectric property is available in the NKL xNT ceramics with high Li content because its To−t was moved below room temperature. [ABSTRACT FROM AUTHOR]

A facile hydrothermal route was adopted for synthesis of lead-free piezoceramics (K, Na)NbO3 powders. The influences of temperature and KOH/NaOH concentration on the resultant powders were investigated. Although two similar perovskite phases appeared when K/Na ratio tended toward 1:1, the two-phase coexistence tendency was weakened by increasing hydrothermal reaction temperature, and consequently only one phase could be obtained after spark plasma sintering. Reasonably good ferroelectric and piezoelectric properties were obtained for the samples after postannealing, whose piezoelectric constant ( d33) reached 135 pC/N. The optimal remnant polarization ( Pr) and mechanical quality factor ( Qm) were 26.2 μC/cm2 and 164, respectively, which were both twice as much as those of the samples using powders prepared from solid-state reaction. [ABSTRACT FROM AUTHOR]

Microstructure characteristics, phase transition, and electrical properties of (Na0.535K0.485)0.926Li0.074(Nb0.942Ta0.058)O3 (NKN-LT) lead-free piezoelectric ceramics prepared by normal sintering are investigated with an emphasis on the influence of sintering temperature. Some abnormal coarse grains of 20–30 μm in diameter are formed in a matrix consisting of about 2 μm fine grains when the sintering temperature was relatively low (980°C). However, only normally grown grains were observed when the sintering temperature was increased to 1020°C. On the other hand, orthorhombic and tetragonal phases coexisted in the ceramics sintered at 980°–1000°C, whereas the tetragonal phase becomes dominant when sintered above 1020°C. For the ceramics sintered at 1000°C, the piezoelectric constant d33 is enhanced to 276 pC/N, which is a high value for the Li- and Ta-modified (Na,K)NbO3 ceramics system. The other piezoelectric and ferroelectric properties are as follows: planar electromechanical coupling factor kp=46.2%, thickness electromechanical coupling factor kt=36%, mechanical quality factor Qm=18, remnant polarization Pr=21.1 μC/cm2, and coercive field Ec=1.85 kV/mm. [ABSTRACT FROM AUTHOR]

We prepared high-density La1.96M0.04CuO4 (M: Mg, Ca, Sr) polycrystalline ceramics by a spark plasma sintering method, and investigated the temperature dependence of the electrical conductivity, Seebeck coefficient, and power factor. Our results indicate that the relative density of these sintered ceramic samples can reach nearly 100%, and alkaline earth metal ions doping can increase the activation energy (from 0.021 to 0.128 eV). All ceramic samples show high positive Seebeck coefficient (∼100–510 μV/K). The obtained Sr-doped La2CuO4 ceramics show better thermoelectric properties, which potentially make them for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Highly dense La2CuO4 ceramics have been prepared by the spark plasma sintering technique. Temperature dependence of electrical conductivity indicates that La2CuO4 ceramics sintered at over 875°C exhibit a metal-like behavior, which should be ascribed to the special La2CuO4 crystal structure and its correlation splitting of the half-filled d x2− y2 band. Our experimental data indicate that all of the La2CuO4 samples exhibit positive thermoelectric power in the whole measuring temperature range, indicating that the majority of charge carriers are holes. It is desirable to obtain good thermoelectric performance for this system by optimizing the electrical properties and reducing the thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Porous piezoceramics have promising applications in underwater sonar detectors or medical ultrasonic imaging. We report the electrical and acoustic properties based on different pore microstructures of porous lead zirconate titanate (PZT) ceramics, fabricated using stearic acid (SA) and polymethylmethacrylate (PMMA) as pore-forming agents. The corresponding ferroelectric and piezoelectric properties decreased with increasing porosity due to the decrease in volume fraction of PZT phase, and were in good agreement with a modified cubes model in the case of isolated porosity. The corresponding acoustic impedance decreased from 16 to 8MRayls (106 kg/m2 s), with increasing porosity from 3% to 43%, due to low acoustic impedance of pore phase. The electrical properties of porous PZT ceramics were closely associated with porosity and the interconnection of pores, but only slightly associated with the shape of pores. However, the acoustic impedance was only connected to porosity, not to either shape or interconnection of pores. [Copyright &y& Elsevier]

Lead-free piezoelectric Na xK1− xNbO3 ( x=20–80 mol%) ceramics were fabricated using spark plasma sintering at a low temperature (920°C). All the Na xK1− xNbO3 ceramics showed a similar orthorhombic phase structure, while the corresponding lattice parameters decreased from the KNbO3 side to the NaNbO3 side with increasing Na content. A discontinuous change in lattice parameter close to composition of 60 mol% Na indicated the presence of a transitional area that is similar to the morphotropic phase boundary (MPB) in Na xK1− xNbO3 ceramics. The sintered density of the Na xK1− xNbO3 ceramics decreased with increasing Na content, from a relative density of 99% for the K-rich side to 92% for the Na-rich side. The piezoelectric constant d33 and planar mode electromechanical coupling coefficient kp showed a maximum value of 148 pC/N and 38.9%, respectively, due to the similar MPB effects in the PZT system. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics have received attention because of increasing interest in environmental protection. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, highly dense Na0.5K0.5NbO3 ceramics were prepared using spark plasma sintering (SPS). Although the SPS temperature was as low as 920°C, the density of the Na0.5K0.5NbO3 solid solution ceramics was raised to 4.47 g/cm3 (>99% of the theoretical density). After post-annealing in air, reasonably good ferroelectric and piezoelectric properties were obtained in the Na0.5K0.5NbO3 ceramics with submicron grains. The crystal phase of the Na0.5K0.5NbO3 has an orthorhombic structure. The Curie temperature is 395°C and the piezoelectric parameter ( d33) of the Na0.5K0.5NbO3 ceramics reached 148 pC/N. [ABSTRACT FROM AUTHOR]

Abstract: Lead-free piezoelectric ceramics based on bismuth sodium titanate (Bi1/2Na1/2)TiO3 (BNT)–barium zirconate titanate Ba(Ti,Zr)O3 (BZT) were prepared by using a modified sintering process. The BNT–BZT ceramics sintered at 1180 °C for 3 h in air showed perovskite structure with high densities around 5.32–5.82 g/cm3 (~97% as relative density). Focusing on the morphotropic phase boundary (MPB) of BNT–BZT system, the ferroelectric, dielectric and piezoelectric properties of the BNT–BZT ceramics were studied. In the case of (Bi1/2Na1/2)TiO3–xBa(Ti0.942Zr0.058)O3 solid solution ceramics, the maximum of piezoelectric constant d 33 (147 pC/N) was obtained for the ceramic with 9% BZT, which has a tetragonal phase near the MPB region. The BNT–BZT system was expected to be a new and promising candidate for lead-free piezoelectric ceramics. [Copyright &y& Elsevier]

Lead magnesium niobium titanate (PMNT) thin films with a composition near the morphotropic phase boundary were prepared on conventional Pt(111)/Ti/SiO2/Si substrates using a modified sol-gel process. A PbO seeding layer was introduced to the interface between the PMNT layer and the substrate to enhance the [001]-preferential orientation of the PMNT film. Single-phase perovskite PMNT films with highly [001]-preferential orientation were obtained at reduced annealing temperatures compared with the PMNT films directly deposited on the same substrates. The dielectric and ferroelectric properties of the prepared PMNT films were evaluated as a function of annealing temperature. [ABSTRACT FROM AUTHOR]

Pressureless sintering of Ti3SiC2 ceramics has been investigated by using mechanically alloyed elemental Ti, Si and C powder mixture as the starting materials. It has been found that mechanical alloying enhanced both the formation of Ti3SiC2 phase and the densification during sintering process. Highly dense Ti3SiC2 ceramics with a relative density up to 99% and a phase purity of ∼80% Ti3SiC2 (TiCx as the secondary phase) were obtained by sintering the mechanically alloyed powders at relatively low temperatures near 1773 K in an argon atmosphere of 0.1 MPa. The physical properties of the present pressureless-sintered Ti3SiC2-based ceramics are comparable to those of nearly single phase Ti3SiC2 ceramics fabricated by the reactive hot-isostatic pressing (HIP) that had been used so far. [ABSTRACT FROM AUTHOR]

Alkaline volatilization during sintering in ( K, Na) NbO3 ( KNN)-based lead-free piezoceramics is a problem that causes non-stoichiometry and hence affects the phase structures and properties. This work investigated the depth-dependent distributions of alkaline elements in Li-modified KNN ceramics using X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that Li evaporated more severely than Na and K, consequently almost no Li elements remained on the as-sintered surface, while its content became stable at the depth over 55 μm from the outmost surface. In addition, X-ray diffraction results suggested the phase structure might show discrepancy at the pellet surface and the interior part due to the textured surface grains. [ABSTRACT FROM AUTHOR]

Highly (00l) oriented Ca3Co4O9-based ceramics were fabricated by spark plasma sintering combined with a dynamic forging process. The grain orientation is effective in lowering the electrical resistivity and enhancing the thermoelectric power factor but with little influence on the Seebeck coefficient. A metallic-to-semiconducting transition temperature can be observed and the activation energy is almost independent of the La-doping. All of the Ca3Co4O9-based ceramic samples exhibit large thermoelectric power, and the figure of merit for La-doped Ca3Co4O9 sample can reach 0.26 at 975 K, which can be a promising candidate of p-type material for high-temperature thermoelectric application. [ABSTRACT FROM AUTHOR]

LiNbO3-doped (Na, K)NbO3 lead-free piezoceramics were prepared by conventional sintering at a temperature as low as 950 °C using excess Na2O additives. The crystal structure changed from orthorhombic to tetragonal with increasing LiNbO3 amount since the phase transition temperature TO-T shifted downward. In the region of two-phase coexistence, enhanced piezoelectric constant d33 (280 pC/N) and electromechanical coupling factor kp (48.3%) with a high Curie temperature TC (475 °C) were obtained in the nominal composition 0.92(Na0.535K0.48)NbO3–0.08LiNbO3. Our results open up the way to low-temperature sintering of (Na, K)NbO3-based lead-free piezoceramics with high performance. [ABSTRACT FROM AUTHOR]

Li/Ta-codoped lead-free (Na,K)NbO3 ceramics with a nominal composition of [(Na0.535K0.480)0.942Li0.058](Nb0.90Ta0.10)O3 were synthesized normally at 1070°–1100°C. The XRD patterns of all samples show a single pervoskite structure with tetragonal symmetry. Although MPB separating the orthorhombic and tetragonal symmetries was absent, the maximum piezoelectric coefficient ( d33), electromechanical coupling coefficient ( kp), Curie temperature ( Tc), and remanent polarization ( Pr) were optimized as 216 pC/N, 38.1%, 445°C, and 8.73 μC/cm2, respectively. [ABSTRACT FROM AUTHOR]

The crystallographic structure of (Na,K)NbO3-based compounds and phase transitional behavior in (1-x)(K0.5Na0.5)NbO3–xLiNbO3 (x=0, 3, 6, and 8 mol %) ceramics were accurately determined using high resolution x-ray diffraction (XRD). The phase transition between orthorhombic and tetragonal was distinctly characterized focusing on the XRD peak changes in {222} and {400} diffraction planes, by which lattice parameters of the perovskite type subcell, a, b, and c as well as angle β can be calculated. The discontinuous change in angle β at x=6 mol % is located at the phase transitional region, where enhanced piezoelectric constant d33=215 pC/N was obtained. The present study provides a precise as well as simple method to investigate crystallographic structures in (Na,K)NbO3-based ceramics. [ABSTRACT FROM AUTHOR]

Mechanical alloying (MA) synthesis of Ti3SiC2 from a stoichiometric elemental powder mixture of Ti, Si, and C was conducted by using a planetary mill with a specially designed MA jar, which enables the real-time measurement of temperature and gas pressure during the MA process. Sudden gas pressure and temperature rises were detected when the mixed powders were mechanically alloyed for a certain period, and consequently a large amount of Ti3SiC2 particles was synthesized. Using the Ti–Si–C system as an example, the present study confirmed the combustion reaction triggered by the ball-milling process for the first time. [ABSTRACT FROM AUTHOR]

Higher manganese silicide (HMS) is a naturally abundant, environmentally friendly, and mechanically robust P-type thermoelectric (TE) semiconductor. Isoelectronic doping elements Re and Ge are used to partially occupy cation (Mn) and anion (Si) sites, respectively. Compared with the single Re-doped strategy, TE performance is further improved in the isoelectronic double-doped Mn 0.96 Re 0.04 (Si 0.96 Ge 0.04) 1.79 composition. The electrical conductivity (∼54.2 × 103 S m–1 at 823 K) is double that of pure HMS (∼26.1 × 103 S m–1), whereas the power factor increases from ∼1.42 × 10–3 W m–1 K–2 to ∼1.80 × 10–3 W m–1 K–2 due to the increase in carrier concentration caused by the decreased band gap (from 0.82 eV to 0.74 eV), as well as the embedding of the Si, Ge nanodispersions with low work functions. Furthermore, the substitution of Re and Ge increases the amounts of lattice defects, and the presence of nanoscale Ge precipitates cause the broadband phonon-scattering effect in the HMS matrix. Finally, the lattice thermal conductivity at 673 K decreases from ∼2.18 W m–1 K–1 to ∼1.60 W m–1 K–1. The zT value at 823 K increases by ∼36% from 0.45 to 0.61. The strategy of cation and anion double doping can effectively improve the TE properties of materials, which has significance for the optimization of other materials. [ABSTRACT FROM AUTHOR]

Abstract: Single-phase polycrystalline La0.08Sr0.92TiO3 ceramics were prepared by spark plasma sintering (SPS) using sol–gel-derived powders. The La0.08Sr0.92TiO3 bulks had highly relative density (∼92%), and the grain size of the samples obviously grew from 300 nm to 3 μm when the SPS temperature increased from 1203 to 1473 K. The electrical conductivity increased with SPS-processing temperature owing to the increase of relative density, grain size, and oxygen vacancies due to the reducing atmosphere of SPS. The absolute value of Seebeck coefficient increased as the SPS temperature increased from 1203 to 1373 K, and then decreased by further increasing SPS temperature to 1473 K. The sample SPSed at 1373 K had the largest absolute value of Seebeck coefficient of 196 μVK−1 at 679 K. Sol–gel process and SPS can significantly decrease the thermal conductivity of SrTiO3 based ceramics, whose lowest value was reduced to 1.19 Wm−1k−1 at 773 K in the sample SPSed at 1203 K. The maximum ZT value of 0.08 was obtained at 679 K for the sample SPSed at 1473 K. [Copyright &y& Elsevier]

Ferroelectric perovskite oxides exhibit the bulk photovoltaic effect, which enables an above-bandgap photovoltage, controllable photocurrent response, and higher efficiencies. Herein, the phase structure, ferroelectric, dielectric, light absorption, and photovoltaic properties in (Ba 0.95 Ca 0.05)(Ti 0.92 Sn 0.08- x Zr x)O 3 (BCTSZ x) ceramics were investigated. All BCTSZ x samples had good ferroelectric properties along with a narrow band gap (E g = 2.53–2.60 eV). A large photovoltaic response under AM 1.5 G simulated sunlight was observed in the poled BCTSZ 0.06 ceramics, in which the maximum short-circuit current (J SC = 3.66 nA cm−2) as well as the highest transient current (J TC = 32.56 nA cm−2) and photocurrent (J PC = 12.63 nA cm−2) were obtained in 500 μm-thick sample negatively poled at 30 kV cm−1. Our results deepen an understanding of the ferroelectric photovoltaic mechanism of perovskite materials and provide a new material for photovoltaic and multifunctional applications. [ABSTRACT FROM AUTHOR]

Abstract The projected increase in world energy consumption within the next 50 years, coupled with low emission requirements, has inspired an enormous effort towards the development of efficient, clean, and renewable energy sources. Efficient electrical energy storage solutions are keys to effective implementation of the electricity generated from these renewable sources. In step with the development of energy storage technology and the power electronics industry, dielectric materials with high energy density are in high demand. The dielectrics with a medium dielectric constant, high breakdown strength, and low polarization hysteresis are the most promising candidates for high-power energy storage applications. Inspiring energy densities have been achieved in current dielectrics, but challenges exist for practical applications, where the underlying mechanisms need to be understood for further enhancing their properties to meet future energy requirements. In this review, we summarize the principles of dielectric energy-storage applications, and recent developments on different types of dielectrics, namely linear dielectrics, paraelectrics, ferroelectrics, and antiferroelectrics, are surveyed, focusing on perovskite lead-free dielectrics. The new achievements of polymer-ceramic composites in energy-storage applications are also reviewed. The pros and cons of each type of dielectric, the existing challenges, and future perspectives are presented and discussed with respect to specific applications. [ABSTRACT FROM AUTHOR]

Abstract (K, Na)NbO 3 (KNN)-based solid solutions are outstanding lead-free piezoelectric materials, yet stable reproduction of these materials has always been an obstacle. In the present study, significant ferroelectric phase coexistence was observed in the polycrystalline ceramic sample after sintering. The ferroelectric phase coexistence can be well explained by the chemical heterogeneity in the calcined powder, which is a consequence of using monoclinic Nb 2 O 5 as the precursor. It was demonstrated that the ferroelectric phase coexistence, as well as the chemical heterogeneity, could be a barrier of the reproducibility of performances. Therefore, we suggest that extra attention should be paid on the processing of KNN-based materials, from the very beginning, that is, the choice of precursors. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Here we observed a large strain of lead-free BiFeO 3 ternary ceramics by the composition design [(0.70- x )Bi 1.05 FeO 3 -0.30BaTiO 3 - x Bi(Mg 2/3 Nb 1/3 )O 3 ]. Positive temperature dependence of strain under E  = 4 kV/mm can be observed in the ceramics with x  = 0.07. Large strain property ( S  = 0.32% and d 33 * = 800 pm/V) and low hysteresis ( H  = 5%) can be achieved in the ceramics measured at 200 °C, which may originate from thermally activated domain switching, electric field-induced relaxor to ferroelectric phase transition, and intrinsic lattice strain. We believe that the lead-free bismuth ferrite ternary ceramics with both large strain properties and small hysteresis are promising for high-temperature actuator applications. [ABSTRACT FROM AUTHOR]

The anisotropies of mechanics and thermodynamics properties of zirconia with three zero-pressure polymorphs were studied by using first-principles calculations. It has been shown that Young’s moduli of three phases strongly depend on directions. The sound velocities of faster mixed mode ( v + ) is much larger than that of slower mixed mode ( v − ) and pure transverse mode ( v t ) in monoclinic phase. For both tetragonal phase and the cubic phase, most pure longitudinal mode ( v l ) have the greatest sound velocity among the three acoustic modes. According to the Clarke's model, three zero-pressure polymorphs zirconia also have pronounced anisotropic minimum thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Co-firing of piezoceramics with metals is drawing ever-increasing attention. This article reports Ni-particle-dispersed [Li0.06(K0.5Na0.5)0.94]NbO3 (LKNN/Ni) lead-free piezoelectric composites that were sintered in a protective atmosphere of nitrogen gas. The base metal Ni was not oxidized and the piezoelectric LKNN preserved the perovskite structure. The microstructure observations show that Ni particles were uniformly dispersed in LKNN ceramics matrix. With increasing Ni content from 0 to 20vol%, the piezoelectric constant d 33 of the LKNN/Ni composites decreased from 165 to 23pC/N, and the corresponding dielectric constant ɛ r greatly increased. The 95%LKNN-5%Ni composite still exhibited a typical ferroelectric loop; however, the P-E curves measured for Ni>5vol% composites demonstrated some metallic characteristics. The LKNN/Ni composites could find applications in piezoelectric actuators with functionally graded microstructure (FGM). [Copyright &y& Elsevier]

Abstract: Recently, apatite-type lanthanum silicate, La9.33(SiO4)6O2, and its analogues with cationic doping in the La/Si site have been attracting significant interests due to their high oxide ion conduction. However, the well-known synthesis method is solid-state reaction, which suffers from problems such as the high sintering temperatures for dense pellets and the impurity phases in the final ceramics. In this paper apatite-type lanthanum silicates were prepared by precipitate method combining with an azeotropic-distillation process. The influences of powder calcination temperature on the relative density were investigated and the optimal calcination temperature was proved to be 1100°C. The main phase of the powder calcined at 1100°C was lanthanum silicate La9.33(SiO4)6O2 with trace impurities La2O3 and La2SiO5. However, dense pellet (96.63%) with pure lanthanum silicate phase was obtained at relatively low temperature (1550°C). Electrical measurements have shown that conductivity behaviors of the sintered pellets were also calcination-temperature dependent. The highest overall conductivity values, σ 500°C =1.58×10−3 Scm−1 and σ 800°C =2.21×10−2 Scm−1, were obtained for pellet prepared from powder calcined at 1100°C, which was much higher than that synthesized by other methods. The samples presented activation energies of 0.66±0.01eV. The results in the present study demonstrate that the precipitate-azeotropic-distillation approach is an alternative method to synthesize lanthanum silicate powders. [Copyright &y& Elsevier]