Rebound behavior of nanoparticle-agglomerates

In general, the rebound behavior of particles depends on the particle/substrate material combination and the particle size. In the present investigation the rebound behavior of nanoparticle agglomerates is investigated in a low pressure impactor and compared to single spherical particles. For agglomerates, their structure and mechanical strength will also affect the rebound behavior. The rebound of openly structured agglomerates (fractal dimension D_f < 2) is determined by the primary particle size and the particle-substrate combination. The impact velocity required for rebound (critical velocity) is independent of the agglomerate size and equal to the critical velocity of single spherical particles having the same size as the primary particles. In case of agglomerate fragmentation no rebound was observed for openly structured agglomerates. For denser agglomerates (D_f > 2), the critical impact velocity decreases with increasing agglomerate size, where the decrease is more accentuated for higher fractal dimensions, finally approaching the behavior of spheres.     

Evaluation of aerosol sizing characteristic of an impactor using imaging plate technique

The activity-size distribution of radon decay products are normally determined using two approaches: direct and indirect. The present study utilises the direct approach to evaluate sizing information of a low pressure cascade impactor using imaging plate (IP) technique for radon decay products. The experiment verified the use of the collection media as suggested by the manufacturer of impactor and proposed a few improvements toward sizing characteristics of impactor. The obtained relative activity-size distribution of radon decay products presents a sharp unimodal log-normal distribution of the particle characterised by activity median aerodynamic diameter (AMAD) of 268 nm and geometric standard deviation (sigma(g)) of 1.66. The obtained data with all the suggested improvements were evaluated by the data obtained from a scanning mobility particle sizer (SMPS, Model 3934, TSI Inc), as reference data. The verification lead to a derivative area ratio of 0.803 between the reference and experimental data.     

Microstructure, dielectric and piezoelectric properties of La-modified Bi0.5(Na0.84K0.16)0.5TiO3 lead-free ceramics

Lead-free ceramics (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ were prepared by a conventional ceramic technique and the effects of La doping and sintering temperature on the microstructure, ferroelectric and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and La³⁺ diffuses into the Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ lattices to form a solid solution with a rhombohedral symmetry. The addition of La leads to the significant change in the grain morphology and size for the (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ and a number of rod grains with the length of 10–50 μm and the diameter of 1–2 μm are observed in the ceramic with x = 0.04 sintered at 1,140 °C for 2 h. However, as sintering temperature increases to 1,160 °C, the rod grains disappears and the uniform and rectangular grains are observed in the ceramics with x = 0.04. As x increases from 0 to 0.06, the coercive field E _c of the ceramics decreases from 4.33 to 2.81 kV/mm and the remanent polarization P _r of the ceramics retains the high values of 25.9–27.7 μm/cm². The depolarization temperature T _d decreases from 154 to 50 °C with x increasing from 0 to 0.10. All the ceramics exhibit the diffusive phase transition at high temperature (280–320 °C). The ceramic with x = 0.04 sintered at 1,150 °C for 2 h exhibit the optimum piezoelectric properties, giving d ₃₃ = 165 pC/N and k _p = 32.9 %. The optimum sintering temperature is 1,150 °C at which the improved piezoelectric properties (d ₃₃ = 165 pC/N and k _p = 32.9 %) are obtained. At the high La³⁺ level (x = 0.10 and 0.12), the ceramics exhibit weak ferroelectricity (P _r = 13.0–21.2 μm/cm²) and thus possess poor piezoelectricity (d ₃₃ = 17–27 pC/N).     

Agglomerates and aggregates of nanoparticles made in the gas phase

Gas-phase (aerosol) technology is used widely in manufacture of various nanostructured commodities at tons/hour today. So it is quite promising for synthesis of sophisticated nanoparticles motivating basic and applied research. Frequently such nanoparticles are made as clusters of primary particles (PPs) by chemical reaction, aerosol coagulation, sintering, surface growth and even fragmentation. When PPs are bonded by strong chemical forces, they are termed aggregates. As such they are sought in catalysis, lightguide preform manufacture and, most importantly, as components in electronic devices (sensors, batteries). When PPs and aggregates are held together by rather weak, physical forces, they form agglomerates. These are attractive in nanocomposites and fluid suspensions (paints, nanofluids, bioimaging). Such clusters may have also distinct health effects, beyond those of equivalent spherical particles.Agglomerates and aggregates are characterized by microscopy, electromagnetic scattering and mass mobility measurements in terms of their volume-equivalent radius, radius of gyration and/or mobility radii in the free molecular and continuum regimes along with the corresponding power laws (fractal dimension, D_f). Coagulation and sintering largely determine nanoparticle structure. Coagulation of PPs leads to agglomerates of D_f = 1.78 and 1.91 in the continuum and free-molecular regimes, respectively. The coagulation rate of agglomerates is higher than that of volume-equivalent spheres in the free molecular regime. Agglomerates attain also a self-preserving size distribution by coagulation facilitating process design for their manufacture. Mesoscale simulations elucidate the sintering (or coalescence) of agglomerates to aggregates and narrowing of their PP size distribution. Once agglomerates start to sinter, they follow a power law to aggregates and eventually to compact (spherical) particles, regardless of composition and initial PP size distribution. Aggregate properties are in-between those of the initial agglomerate and the fully coalesced sphere. Finally the stability of agglomerates under ultrasonication, stretching, fluid dispersion, impaction and capillary condensation is highlighted.     

Size effect on piezoelectric properties of barium stannate titanate ceramics prepared from nanoparticles

Piezoelectric properties of Ba(Ti_1?x Sn _x )O₃ ceramics with x = 0.025, 0.045 and 0.065, prepared from 16 nm powders, were compared with those of the corresponding ceramics obtained from 86 nm powders to see the effect of tin content and particle size of the starting powders. Ba(Ti_1?x Sn _x )O₃ powders were synthesized by solid state reaction of BaCO₃, TiO₂ and SnO₂ at 1,050 °C. The powders were high energy ball milled to produce nanocrystalline powders having average particle size of 16 nm. The milled powders were sintered at 1,350 °C for 4 h to yield ceramics. For these ceramics, increasing Sn content from x = 0.025–0.065 produces a decrease in (1) unipolar strain level s from 0.084 to 0.027 %, and (2) electromechanical coupling factor k _p from 33.6 to 19.3 %. However, the bulk density, room temperature dielectric constant and piezoelectric charge constant d ₃₃ exhibit an increase from 5.03–5.84 g/cm³, 1,342–2,156 and 7–110 pC/N, respectively, with increasing Sn content. The increasing trend of density and d ₃₃ presently observed is in sharp contrast to the result of corresponding ceramics prepared from 86 nm nanopowders. The present study reveals a cooperative mechanism involving both the nanoscale size of the starting particles and optimum tin content which results in the enhancement of d ₃₃ with tin content.     

Grain growth,densification and electrical properties of lead-free piezoelectric ceramics from nanocrystalline (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 powder by sol–gel technique

The sintering behavior revealed in the sintering processes of the conventional and a two-step process and electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from the nanocrystalline powders synthesized by a sol–gel technique were systematically studied. It was found that the sintering process of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics made from nanocrystalline powders was significantly improved, the sintering temperature was reduced markedly from 1,540 to 1,280 °C, as well as a high relative density (>97 %) was obtained in the conventional sintering. Under the two-step sintering conditions, the full densification and the most suppression of grain growth was achieved simultaneously. The (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from nanocrystalline powders sintered by the two-step sintering technique (sintered at T ₁ of 1,300 °C for 1 min and T ₂ of 1,150 °C for 20 h) exhibited the optimum average grain size of 700 nm and a high relative density of 98 %. The electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics were greatly influenced by the grain size and phase structure formed under the both sintering conditions, with sintering temperature and grain size increased, the electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics, which made from nanocrystalline powders, shows an enhancing trend: d ₃₃ ~100 pC/N, k _p ~53.3 % for the specimen sintered at 1,300 °C for 1 min and 1,150 °C for 20 h, d ₃₃ ~310 pC/N, k _p ~53.3 % for the specimen sintered at 1,350 °C for 2 h respectively.     

Metal nanoparticle-loaded porous carbon hollow spheres by twin polymerization

The formation of silver and gold nanoparticle-encapsulated hollow carbon spheres (HCS) by twin polymerization is reported. Therefore, silica spheres with different diameters (Aerosil^® AS90, d = 20 nm; Aerosil^® OX50, d = 40 nm; Stöber particles, d = 200 nm) were coated with the metal carboxylates [AgO₂C(CH₂OCH₂)₃H] (1) or [(PPh₃)AuO₂C(CH₂OCH₂)₃H] (2). Thermal treatment of the as-produced templates gave the respective metal nanoparticle-functionalized systems, which were characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy. The plasmon resonance of the surface-bonded particles was determined by using UV–Vis spectroscopy showing absorptions at 412 nm for silver and 524 nm for gold. The metal nanoparticle-modified templates were then coated with a twin polymer layer as result of the acid-catalyzed twin polymerization of 2,2′-spiro-bi[4H-1,3,2-benzodioxasiline] (3). This coating consists of a phenolic resin and in situ formed silicon dioxide nanoclusters. After carbonization and removal of the SiO₂ phase by refluxing with a NaOH solution, the appropriate metal-loaded HCS were obtained. The thus prepared carbon materials were characterized by PXRD, electron microscopy and nitrogen adsorption–desorption isotherms. Mainly micro-porous materials (IUPAC type I) were obtained with a surface area between 910 and 1110 m²/g. These HCS materials were used for the catalytic reduction of methylene blue and 4-nitrophenol proving the accessibility of the incorporated M-NPs. A size-dependent influence of the used carbon hull was found.     

Correlation Between Band Structure and Magneto- Transport Properties in HgTe/CdTe Two-Dimensional Far-Infrared Detector Superlattice

Theoretical calculations of the electronic properties of n-type HgTe/CdTe superlattices (SLs) have provided an agreement with the experimental data on the magneto-transport behaviour. We have measured the conductivity, Hall mobility, Seebeck and Shubnikov-de Haas effects and angular dependence of the magneto-resistance. Our sample, grown by MBE, had a period d=d ₁+d ₂ (124 layers) of $d_{1}=8.6~\mathrm{nm}~\mathrm{(HgTe)} /d_{2}=3.2~\mathrm{nm}~\mathrm{(CdTe)}$ . Calculations of the spectras of energy E(d ₂), E(k _z ) and E(k _p ), respectively, in the direction of growth and in plane of the superlattice; were performed in the envelope function formalism. The energy E(d ₂,Γ,4.2 K), shown that when d ₂ increase the gap E _g decrease to zero at the transition semiconductor to semimetal conductivity behaviour and become negative accusing a semimetallic conduction. At 4.2 K, the sample exhibits n type conductivity, confirmed by Hall and Seebeck effects, with a Hall mobility of $2.5 \times 10^{5}~\mathrm{cm}^{2}/ \mathrm{V\,s}$ . This allowed us to observe the Shubnikov-de Haas effect with n=3.20×10¹² cm^?2. Using the calculated effective mass ( $m^{*}_{E1}(E_{F}) = 0.05 m_{0}$ ) of the degenerated electrons gas, the Fermi energy (2D) was E _F =88 meV in agreement with 91 meV of thermoelectric power α. In intrinsic regime, α～T ^?3/2 and R _H T ^3/2 indicates a gap E _g =E ₁?HH ₁=101 meV in agreement with calculated E _g (Γ,300 K)=105 meV. The formalism used here predicts that the system is semiconductor for d ₁/d ₂=2.69 and d ₂<100 nm. Here, d ₂=3.2 nm and E _g (Γ,4.2 K)=48 meV so this sample is a two-dimensional modulated nano-semiconductor and far-infrared detector (12 μm<λ _c <28 μm).     

Dielectric and piezoelectric studies of perovskite-tungsten bronze structured (1 − x)[0.5PMN-0.5PZT]-xPBBiN nanoceramic composites by high-energy mechanical activation technique

In this paper, phase development, dielectric and piezoelectric properties of nanocomposites consisting of perovskite structured PMN-PZT and tungsten bronze structured PBBiN synthesized via high energy mechanical activation technique were examined as a function of x in (1 ? x)(0.5PMN-0.5PZT)-xPBBiN with a stoichiometric formula as (1 ? x)[0.5Pb(Mg_0.33Nb_0.67)O₃-0.5Pb(Zr_0.53Ti_0.47)O₃]-x[Pb_0.59Ba_0.38Bi_0.02Nb₂O₆]. It was observed that the high-energy mechanical activation technique has greatly improved the reactivity of the precursors by reducing the phase formation temperatures and eliminating unwanted secondary phases and liquid phase sintering as x increased. Powder X-ray diffraction studies of the ternary system revealed the perovskite cubic (PMN-PZT) coexisted with tungsten bronze orthorhombic (PBBiN) phase. The average particle size ranged from 22 to 81 nm. A combination of both perovskite and tungsten bronze grains revealed intragranular and intergranular growth which accelerated densification and homogeneity in the nanocomposite. The dielectric (ε_RT = 2,248) and piezoelectric properties (d ₃₃ = 412 pC/N and k _p = 0.446) obtained were maximum at x = 0.4 which could be suitable for possible electromechanical and energy harvesting applications.     

Enhancement of dielectric and magnetic properties in phase pure,dense BiFeO<Subscript>3</Subscript> nanoceramics synthesized by spark plasma sintering techniques

Phase pure, dense BiFeO₃ (BFO) ceramics with average grain sizes of ~?110 nm, ~?450 nm, and ~?1.15 µm were fabricated by spark plasma sintering method. BFO ceramics exhibited grain-size-dependent magnetic properties, which ascribed to the antiferromagnetism–ferromagnetism (AFM–FM) transition. For BFO nanoceramics (~?110 nm), such transition was much significant, and contributed to a large exchange bias field of H_EB?=?500 Oe at 5 K. In addition, BFO nanoceramics (~?110 nm) exhibited lower leakage current and higher resistivity compared to the larger-grained BFO ceramics (~?450 nm and ~?1.15 µm). The calculated activation energies (E_a) and X-ray photoelectron spectroscopy analyses revealed the existence of different types of defects in BFO ceramics with different grain sizes.     

Enhanced photocatalytic activity of BiFeO3 particles by surface decoration with Ag nanoparticles

BiFeO₃ particles with different morphologies and sizes were synthesized via a hydrothermal process, where the morphology and size was tailored by using different KOH concentrations in precursor solution. The samples prepared at n(KOH) = 3, 4.5, 6, and 7.5 M are composed, respectively, of octahedron-shaped particles (500–600 nm), cube-like particles (200–500 nm), irregular spherical agglomerates (9–16 μm) formed from disk-like grains with diameter of 1.4–2.8 μm and thickness of 0.2 μm, and cuboid-shaped particles with length-to-width ratio of 1.4:1–3.5:1 and width size ranging from 80 to 280 nm. Ag nanoparticles were deposited on the surface of BiFeO₃ particles by a chemical reduction method to produce Ag@BiFeO₃ nanocomposites. The photocatalytic activity of prepared samples was evaluated by degrading rhodamine B under simulated sunlight irradiation. It is demonstrated that Ag-decorated BiFeO₃ particles exhibit an enhanced photocatalytic activity compared to bare BiFeO₃ particles. This can be explained by the effective transfer of photogenerated electrons from the conduction band of BiFeO₃ to Ag nanoparticles and hence increased availability of holes for the photocatalytic reaction. Hydroxyl radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and are found to be produced over the irradiated BiFeO₃ and Ag@BiFeO₃ photocatalysts; especially, an enhanced yield is observed for the latter.     

Preparation and piezoelectric properties of CuO-doped (Na0.5K0.5)NbO3 ceramics by the citrate precursor method

A low-cost citrate so-gel route was investigated to synthesize nano-sized crystalline powders (<100 nm) of 1 mol% CuO modified (Na_0.5K_0.5)NbO₃ compositions. It was found that amorphous gels can be transformed into crystallite powders with single-phase perovskite structure when calcined at 500?C600 °C for 3 h. The transmission electron microscopy observation showed that the particles are column-like and well dispersed, depending on the calcination condition. The as-pressed samples exhibit improved densification behavior and finer grain morphology after sintering. Electrical properties of the samples sintered at 1,060 °C are as follows: dielectric constant ?? _r  = 605, piezoelectric constant d ₃₃ ~ 117 pC/N, planar electromechanical coupling factor k _p  ~ 0.38 and mechanical quality factor Q _m  ~ 725.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

Low temperature sintering and properties of lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics with Ba(Cu0.5W0.5)O3 addition

The low-temperature sintering behavior of (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ (BCZT) piezoelectric ceramics with Ba(Cu_0.5W_0.5)O₃ (BCW) addition has been investigated. The addition of 0.1 wt% BCW promotes the sinterability of BCZT ceramics owing to the generation of a liquid phase, resulting in a reduction of sintering temperature from 1,540 to 1,350 °C. The piezoelectric coefficient (d ₃₃), and the electromechanical coupling factor (kp) of the BCZT ? 0.1 wt%BCW specimen sintered at 1,350 °C were 555 pC/N and 55 %, respectively, while Curie temperature (Tc) increases from 85 to 95 °C.     

Structure and piezoelectric properties of K0.5Na0.5NbO3–AlFeO3 lead-free ceramics by using AlFeO3 as a sintering aid

The (1 ? x)K_0.5Na_0.5NbO₃–xAlFeO₃ ((1 ? x)KNN–xAF) (x = 0.01–0.08) lead-free piezoelectric ceramics were prepared at low temperature of 1,000 °C by conventional ceramic processing. And AF was used as a sintering aid in order to improve the sintering behavior of KNN. The effect of AF addition on the microstructure, dielectric and piezoelectric properties of the ceramics have been investigated. The results indicate that a small amount of AF can improve the sintering performance and piezoelectric properties of the ceramics effectively. The KNN–AF ceramics for x = 0.03 show the best piezoelectric properties: d ₃₃ = 116 pC/N, k _p  = 32.9 %, Q _m  = 114.8, T _C  = 382 °C, P _r  = 21.8 μC/cm². This also indicates that (1 ? x)KNN–xAF ceramics are a promising lead-free piezoelectric candidate material because of its good properties, low-temperature sintering characteristics and plenty of Al₂O₃ and Fe₂O₃ resources with low cost.     

High piezoelectric coefficient of Ba0.85Ca0.15Ti0.90Zr0.10O3−Sr(Cu1/3Ta2/3)O3 ceramics

The (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ? x   wt% Sr(Cu_1/3Ta_2/3)O₃ [BCZT ? x  wt% SCT, x = 0–0.3] lead-free ceramics were prepared by the conventional solid-state method. The phase structure was investigated by X-ray diffraction. The results show that only a tetragonal phase is observed in these ceramics. The sintering behavior of BCZT ceramics is also improved by using SCT as a sintering aid. The ceramic with x  = 0.2 wt% SCT demonstrates good piezoelectric properties:d₃₃ ~ 577 pC/N and k_p ~ 59.1 %, Furthermore, the Curie temperature of the ceramics also increases and reaches 97 °C.     

Particle formation in ambient MALDI plumes

The ablated particle count and size distribution of four solid matrix materials commonly used for matrix-assisted laser desorption ionization (MALDI) were measured with a scanning mobility particle sizer (SMPS) combined with a light scattering aerodynamic particle sizer (APS). The two particle sizing instruments allowed size measurements in the range from 10 nm to 20 μm. The four solid matrixes investigated were 2,5-dihydroxybenzoic acid (DHB), 4-nitroaniline (NA), α-cyano-4-hydroxycinnamic acid (CHCA), and sinapic acid (SA). A thin film of the matrix was deposited on a stainless steel target using the dried droplet method and was irradiated with a 337 nm nitrogen laser at atmospheric pressure. The target was rotated during the measurement. A large number of nanoparticles were produced, and average particle diameters ranged from 40 to 170 nm depending on the matrix and the laser fluence. These particles are attributed to agglomeration of smaller particles and clusters and/or hydrodynamic sputtering of melted matrix. A coarse particle component of the distribution was observed with diameters between 500 nm and 2 μm. The coarse particles were significantly lower in number but had a total mass that was comparable to that of the nanoparticles. The coarse particles are attributed to matrix melting and spallation. Two of the compounds, CHCA and SA, had a third particle size distribution component in the range of 10 to 30 nm, which is attributed to the direct ejection of clusters.     

Effects of MnO2 and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ + xmol% MnO₂ lead-free ceramics have been prepared by a conventional sintering method and the effects of MnO₂ and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ lead-free ceramics have been studied. The addition of 0.25 mol% MnO₂ promotes grain growth, improves the ferroelectricity of the ceramics and strengthens ferroelectric tetragonal–ferroelectric orthorhombic phase transition near 40 °C. Because of the coexistence of tetragonal and orthorhombic phases and the combinatory effects of soft and hard doping of Mn ions, the ceramic with x = 0.25 exhibits the optimum piezoelectric properties (d ₃₃ = 306 pC/N and k _p = 42.2 %, respectively). Excess MnO₂ inhibits the grain growth and degrades the ferroelectric and piezoelectric properties of the ceramics. Sintering temperature has an important influence on the microstructure, tetragonal–orthorhombic phase transition near 40 °C, ferroelectric and piezoelectric properties of the ceramics. The increase in sintering temperature leads to large grains and more noticeable tetragonal–orthorhombic phase transition near 40 °C, enhances ferroelectricity and thus improves effectively the piezoelectricity of the ceramics. The Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ ceramic sintered at 1350 °C possesses the optimum piezoelectric constant d ₃₃ value of 373 pC/N.     

Dependence of thermal conductivity in micro to nano silica

This work presents the measurement of thermal conductivity of nano-silica particles using needle probe method. The validation test of thermal probe was conducted on ice and THF hydrates using our experimental set up and the results are satisfactory when compared with the literature data. The nano silica used in this study is with particle sizes in the range 50–1000 nm. The sand powders sieved in different sizes ?<75 and 75  μ m ?>? d ?>? 250  μ m were also studied to probe the particle size dependence on thermal conductivity. Thermal conductivity decreased by about 70% in silica nano powders.     

Microstructure and piezoelectric properties of NaF-doped K0.5Na0.5Nb0.95Ta0.05O3 lead-free ceramics

The effects of NaF on the microstructure and electrical properties of K_0.5Na_0.5Nb_0.95Ta_0.05 lead-free ceramics prepared by conventional sintering method were investigated in this study. The dopant NaF effectively lowers the sintering temperature and promotes the grain growth. Samples with a high relative density up to 96.3 % are achieved by adding 0.6 wt% NaF to improve the sinterability. The electric properties are also enhanced, and the optimum properties are achieved at the doping content of 1.0 wt% (d ₃₃ = 153 pC/N, k _P = 32.2 %, Q _m = 80.5, E _c = 0.89 kV/mm, and P _r = 16.5 μC/cm²). The improvement of ferroelectric and piezoelectric properties is suggested to be largely contributed to the compensation of sodium element from dopant NaF for the volatilization of A-site alkali elements.