Translucent PMN and PMN-PT ceramics from high-energy ball milling derived powders

Translucent PMN and PMN-PT ceramics were prepared from nano-sized powders produced by a high-energy ball milling process. A two-step process was used to achieve the translucent PMN and PMN-PT ceramics, in which samples were sintered at 950°C for 1 h at first and then annealed at 1100°C for 6-24 h. Transmittances at 600 nm wavelength of the PMN, PMN-0.10PT and PMN-0.35PT ceramics annealed for 12 h were 21, 16 and 11%, respectively. The formation mechanism of translucent PMN and PMN-PT ceramics in the present work is similar to that of transparent PLZT ceramics.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

(1 − x)PNZ-xBT ceramics derived from mechanochemically synthesized powders

Nanosized (1−x)Pb(Zn_1/3Nb_2/3)O₃-xBaTiO₃ (PZN-BT, x=0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) powders were synthesized directly from their corresponding oxide mixture via a high-energy ball milling process. Almost single phase was achieved in the composition range of PZN-BT. The grain size estimated from SEM observation was about 50 nm, being in good agreement with that (20 nm) calculated from XRD patterns. PZN-BT ceramics were also obtained by sintering the synthesized powders at 1050°C for 1 h. The grain size of the final ceramics decreases from 4.5 to 1.2 μm as BT content increases from 0.05 to 0.30. The properties, such as microstructure, lattice constant, phase composition, dielectric constant as a function of composition of the PZN-BT ceramics, were investigated and discussed.     

Barium titanate nanoparticles produced by planetary ball milling and piezoelectric properties of corresponding ceramics

Barium titanate (BaTiO₃) nanocrystalline powders were prepared by solid state reaction route starting from BaCO₃ and TiO₂ powders accompanied by high-energy ball milling. Different samples were prepared by varying the milling time from 1 h to 30 h, keeping the milling speed fixed at 250 rpm. All the milled powders were examined with TEM. The particle size first decreases from 105 nm to a minimum of 28 nm as the milling time increases from 1 h to 20 h and then increases to 38 nm with further increase of milling time to 30 h. Dense ceramics were formed by sintering the nanopowders at 1350 °C for 4 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 5.65 g/cc to 5.84 g/cc, coercive field (E_c) from 2.25 kV/cm to 4.77 kV/cm and piezoelectric charge constant (d₃₃) from 99pC/N to 121pC/N.     

Lead-free piezoelectric ceramics manufactured from tantalum-substituted potassium sodium niobate nanopowders

Nanopowders of lead-free (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) system were prepared by high-energy ball milling at different milling times keeping the milling speed fixed at 250 rpm. The particle size first decreases from 35 nm to 3 nm and then increases to 98 nm as the milling time increases in steps of 5 h from 10 h to 30 h. Without using any sintering aid, dense ceramics were formed by sintering the powders at 1050 °C for 1 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 93.1% to 95.8%, coercive field (E_c) from 10.9 kV/cm to 15.1 kV/cm, electromechanical coupling factor (k_p) from 35% to 48%, and piezoelectric charge constant (d₃₃) from 80 pC/N to 128 pC/N. The systematic changes observed in these parameters corroborate the observed increase in particle size as the milling time increases from 25 h to 30 h.     

Preparation and characterization of Y3Al5O12 (YAG) nano-powder by co-precipitation method

YAG precursor was synthesized by a co-precipitation method from a mixed solution of aluminum and yttrium nitrates with aqueous ammonia as the precipitator. The structure, phase evolution and morphology of YAG precursor and the sintered powders were studied by means of IR, TG/DTA, XRD, TEM methods. It was found the precursor with approximate composition of Al(OH)₃·0.3[Y₂(OH)₅·(NO₃)₂·2H₂O] directly transformed to pure-YAG phase at 800 °C and no intermediate phases were detected. YAG nanocrystalline powders from sintering the precursor at different temperatures were less-aggregated and the diameters of the grains were about 40-100 nm. BET surface area of the particles decreased with increase of calcination temperature and the powder sintered at 800 °C can be used for fabrication of transparent YAG ceramics.     

Synthesis and characterization of (Na0.85K0.15)0.5Bi0.5TiO3 ceramics by different methods

The (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (BNKT) powders were synthesized by solid-state method, sol-gel method and stearic acid method. Microstructure, piezoelectric and dielectric properties of the ceramics were investigated. Attempts had been made to understand the reaction processes by using thermo gravimetric (TG) and differential scanning calorimetry (DSC). The BNKT powders have a perovskite structure with average crystallite sizes of 168 nm, 85 nm and 79 nm, corresponding to the solid-state method, the sol-gel method and the stearic acid method, respectively. The ceramics derived from the powder synthesized by sol-gel method presents the most homogeneous microstructure and largest grain size (5-7 μm). The effects of average crystallite size on microstructures and electric properties of the BNKT ceramics were investigated. Both the piezoelectric properties and dielectric properties were enhanced with the increase of grain size.     

Mechanochemical synthesis and characterization of nanocrystalline 0.4Bi(Zn1/2Ti1/2)O3-0.6PbTiO3 powders

Perovskite 0.4Bi(Zn_1/2Ti_1/2)O₃-0.6PbTiO₃ (BZT-PT) powders were successfully synthesized from precursor oxides using a high-energy planetary ball milling. The phase development of the powders during milling was studied by means of X-ray diffraction and Raman scattering techniques. The microstructure of the powders was characterized using transmission electron microscopy, and the thermal behavior was studied as well. The results reveal that after 15 h of milling the formation of BZT-PT phase can be completed and submicron agglomerates of small crystallite sized ~ 12 nm are present in the powders. However, further prolonging the milling time to 25 h leads to the amorphization of the BZT-PT phase.     

Lead zinc niobate (PZN)-barium titanate (BT) ceramics from mechanochemically synthesized powders

Nanosized PZN-BT powders were synthesized directly from their constituent component oxide mixture via a high-energy ball milling process. XRD patterns showed that perovskite phase could be formed after milling for 5 h, while single phase perovskite was achieved when the milling was prolonged for 12 h. Further increase in milling time (20 h) led to the formation of pyrochlore phase. PZN-BT ceramics were obtained by sintering the milled powders at temperatures from 1000 to 1100°C for 1 h. The 1100°C-sintered PZN-BT samples derived from the 12 h milled powders have a density of ∼99% of the theoretical density with an average grain size of about 4 μm, a dielectric constant of 2300 and a dielectric loss of 0.03, being in good agreement with the reported results for PZN-BT prepared by the conventional solid-state reaction process.     

Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO3 ceramics

We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO₃ ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 °C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO₃ ceramics could be reduced to 1100 °C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO₃ ceramics with a high permittivity (?_r = 2946 and ?_max = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO₃ ceramics.     

Synthesis of BF–PT perovskite powders by high-energy ball milling

0.7BiFeO₃–0.3PbTiO₃ (BF–PT) powders were synthesized from a mixture of the oxides Bi₂O₃, Fe₂O₃, PbO and TiO₂ using a Fritsch P4™ vario-planetary ball milling system. The perovskite structure of the BF–PT powder can be obtained well and the crystallite size of the powders was greatly reduced to 20–35 nm after milling for 8 h. The pre-calcined course shows a rhombohedral–tetragonal phase transition with the increasing temperature and shows the structure transition near the Curie temperature T_c.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

Solid state and solution synthesis of Ba(Mg1/3Ta2/3)O3: A comparative study

Ba(Mg_1/3Ta_2/3)O₃ [BMT] dielectric ceramics are prepared by solid state (one step, two step and molten salt synthesis) and wet chemical methods (precipitation, citrate gel and sol-gel). The formation mechanism of BMT in each synthesis technique is discussed. The formation temperature and particle size of the formed BMT were found to be much lesser (in nanometer range) for solution synthesized powders. It is found that synthesis by sol-gel method resulted in the formation of ultra pure nanopowders of BMT at about 600 °C with average crystallite size of about 18 nm where as in solid state synthesis the formation of BMT was formed at about 1100 °C with average crystallite size of 220 nm. On sintering these powders, densification and grain growth of the chemically derived powders were found to be lower than that of solid state synthesized BMT powder. This has resulted in a slight decrease in density and microwave dielectric properties of the solution synthesized BMT samples. It is found that the microwave dielectric properties improved with increase in the average grain diameter of the sintered BMT ceramics.     

Synthesis and structural properties of Ni–20Cr–2Y2O3 nanocomposite alloy prepared by a very high energy mechanical milling

Ni–20Cr–2Y₂O₃ nanocomposite alloys were synthesized by a very high energy ball milling (applied milling energy, ∼180 kJ g⁻¹ hit; milling speed, ∼1000 rpm) using the coarse yttria (Y₂O₃; ∼50 μm) starting powders, and their formation behavior was investigated with particular attention paid to Y₂O₃ particles. Homogeneous Ni–20Cr–2Y₂O₃ nanocomposite alloy powders were achieved in a short milling time of 40 min; the Cr elements were almost fully alloyed into the Ni lattice, and simultaneously the original coarse cubic Y₂O₃ particles were transformed into extremely fine monoclinic nanocrystals. Thermal consolidation by spark plasma sintering induced homogeneous precipitations of the Y–Cr–O nano-clustered oxides (mean diameter d_m ∼12 nm), which were identified as an orthorhombic YCrO₃ structure (space group Pnma, a = 0.5523 nm).     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.     

A modified synthesis method of manganese perovskite La0.67Ca0.33MnO3 by high energy ball milling and post heat treatment

A modified synthesis method of La_0.67Ca_0.33MnO₃ by high energy ball milling and post sintering is reported. The characteristics of samples from this modified method are also studied. The new synthesis method has some advantages including reducing the synthesis procedure into two simple steps, shortening the sintering time, and obtaining similar properties compared with conventional synthesis method. High energy ball milling was employed for 10 h to refine the starting materials into a sub-micron particle size (for comparison, samples milled for 30 and 50 h were also synthesized); during the process, ethanol was added as a milling medium for avoiding amorphization or crystallization, as well as suspending the starting powders for more profound milling. Finally, the as-milled powder was sintered in air to crystallize. The samples show metal-to-insulator transitions at around 260 K, with grain size from 200 nm to 8 μm, and exhibit large magnetoresistance up to 21% at a magnetic field of 3000 Oe near the transition temperature. The possible mechanism is discussed.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

A new and effective chemical reduction method for preparation of nanosized silver powder and colloid dispersion

Nanosized uniform silver powders and colloidal dispersions of silver were prepared from AgNO₃ by a chemical reduction method involving the intermediate preparation of Ag₂O colloidal dispersion in the presence of sodium dodecyle sulfate CH₃(CH₂)₁₁OSO₃Na as a surfactant. Several reducing agents such as hydrazine hydrate (N₂H₄·H₂O), formaldehyde (HCOH) and glucose (C₆H₁₀O₅) have been found to be preferable in this study from a practical point of view. The silver powder with the 60-120 nm particle size and colloidal dispersion with the particles size 10-20 nm and 0.5-2.0 wt.% concentration were successfully synthesized.     

Effects of ball milling on microstructure and electrical properties of sol–gel derived (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

A citrate sol–gel method was investigated for synthesizing lead-free piezoelectric compositions of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNT) and the effect of ball milling on the sintering, microstructure and electrical properties of BNT ceramics was emphasized. The thermal analysis and X-ray diffraction results show that crystalline powders with a single perovskite structure can be obtained when calcined at 600 °C for 3 h. The average particle size of as-calcined powder and electrical properties of sintered samples were obviously dependent on an additional ball milling. Because of well-dispersed superfine powders (∼100 nm), the BNT ceramics can be well densified at temperature 50 °C lower than that by mixed-oxide method and conventional sol–gel method and as a result exhibit enhanced electrical properties of a piezoelectric constant d₃₃ ∼ 180 pC/N and a planar electromechanical coupling factor k_p ∼ 0.29.     

Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 °C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T_f) for the oxidant and fuels were calculated to be 896 °C and 1035 °C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m²/g) compared to the stoichiometric urea-calcium nitrate system (10.50 m²/g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.