Effects of calcination conditions on phase and morphology evolution of lead zirconate powders synthesized by solid-state reaction

Lead zirconate (PbZrO₃) powder has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The effects of calcination temperature, dwell time and heating/cooling rates on phase formation, morphology, particle size and chemical composition of the powders have been investigated by TG-DTA, XRD, SEM and EDX techniques. The results indicated that at calcination temperature lower than 800 °C minor phases of unreacted PbO and ZrO₂ were found to form together with the perovskite PbZrO₃ phase. However, single-phase PbZrO₃ powders were successfully obtained at calcination conditions of 800 °C for 3 h or 850 °C for 1 h, with heating/cooling rates of 20 °C/min. Higher temperatures and longer dwell times clearly favored the particle growth and formation of large and hard agglomerates.     

Influence of calcination conditions on phase formation and particle size of indium niobate powders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. Single-phase InNbO₄ powders have been obtained successfully for calcination condition of 900 °C for 4 h or 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Effects of calcination conditions on phase formation and particle size of indium niobate nanopowders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG–DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that single-phase InNbO₄ powders have been obtained successfully at the calcination condition of 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Effects of milling time and calcination condition on phase formation and particle size of lead zirconate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead zirconate (PbZrO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. A combination of the milling time and calcination conditions was found to have a pronounced effect on both the phase formation and particle size of the calcined PbZrO₃ powders. The calcination temperature for the formation of single-phase perovskite lead zirconate was lower when longer milling times were applied. The optimal combination of the milling time and calcination condition for the production of the smallest nanosized (∼28 nm) high purity PbZrO₃ powders is 35 h and 750 °C for 4 h with heating/cooling rates of 30 °C/min, respectively.     

Phase and morphology evolution of magnesium niobate powders synthesized by solid-state reaction

Magnesium niobate (MgNb₂O₆; MN) powders have been prepared and characterized by TG-DTA, XRD, SEM and EDX techniques. The effect of calcination temperature, dwell time and heating/cooling rates on phase formation, morphology and chemical composition of the powders are examined. The calcination temperature and dwell time have been found to have a pronounced effect on the phase formation of the calcined magnesium niobate powders. It has been found that the minor phases of unreacted MgO and Nb₂O₅ phases tend to form together with the columbite-type MgNb₂O₆ phase, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a single-phase MgNb₂O₆ in an orthorhombic phase. Higher calcination times and heating/cooling rates clearly favoured particle growth and the formation of large and hard agglomerates.     

Effects of milling time and calcination condition on phase formation and particle size of lead titanate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead titanate (PbTiO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. Powder samples were characterized using XRD, SEM, TEM and EDX techniques. A combination of the milling time and calcination conditions was found to have a pronounced effect on the phase formation and particle size of the calcined PbTiO₃ powders. The calcination temperature for the formation of single-phase perovskite lead titanate was lower when longer milling times were applied. More importantly, by employing an appropriate choice of the milling time and calcination conditions, perovskite lead titanate (PbTiO₃) nanopowders have been successfully prepared with a simple solid-state reaction method.     

Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr_xBa_1-xNb₂O₆ (with x = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.     

Effect of mechanical activation on the formation of lead titanates from PbCO3 – TiO2 mixtures

PbTiO₃ powders have been prepared by mild annealing (2h at 600°C) of PbCO₃:TiO₂ mixtures previously subjected to mechanical activation, while a thermal treatment of about 12h at T > 850°C is needed to obtain PbTiO₃ from a physical mixture. Although the temperature and enthalpy of the DSC peak corresponding to PbCO₃ decomposition are not affected by mechanical energy, in the case of the mechanically activated mixtures an exothermic event due to the reaction PbO + TiO₂ → PbTiO₃ shows up. Furthermore, SEM micrographs and the XRD line broadening allow to conclude that PbTiO₃ powders obtained from activated mixtures are of nanometer size. PbTi₃O₇ has been prepared starting from mechanically activated PbCO₃:3TiO₂ mixtures by 1h annealing at 850°C while 100h at 800°C were required to yield this compound from unmilled mixtures.     

A low temperature route to prepare LaMnO3

A combination of digestion and further low temperature calcination to crystallize the product is employed to prepare LaMnO₃(LM) ceramics. Freshly co-precipitated lanthanum and manganese hydroxides gel is allowed to react at 100 °C under refluxing and stirring conditions for 6–12 h. The X-ray amorphous product so formed is heated at 300 °C to form crystalline LM powders. This is the lowest temperature so far reported for the formation of LaMnO₃. Transmission electron microscope (TEM) investigations revealed that the average particle size is 50 nm for the calcined powders.     

Effect of excess Pb on formation of perovskite-type 0.67Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-0.33PbTiO<Subscript>3</Subscript> powders synthesized through a sol–gel process

Perovskite-type 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMNT) powders were fabricated by using a sol–gel process. Excess Pb(CH₃COO)₂·3H₂O (0, 2, 5, 10 or 15 mol%) was added to starting materials to compensate PbO loss from volatilization during heat treatment. X-ray diffraction (XRD) was employed to investigate the effect of excess Pb on the perovksite phase formation of the PMNT powders. It was found that the optimal level of the excess Pb content is 5 mol%. When the raw materials contained 5 mol% excess Pb, the PMNT powders of purest perovskite form was obtained at the calcination temperature of 850 °C. In the PMNT powders, most part of the intermediate phase was Pb-rich pyrochlore Pb₂Nb₂O₇ which was transformed into perovskite phase after calcination at 650 °C, while the residual pyrochlore phase was Pb-deficient Pb₃Nb₄O₁₃ which required calcination at a higher temperature (650–850 °C) to transform into perovskite phase. Compared with the conventional solid-state reaction methods and the solution-based methods reported previously, the present sol–gel route is better at synthesizing PMNT powders of perovskite phase at a low temperature.     

A comparative study of ZnNb2O6 nanoceramics synthesized by high energy ball milling and subsequent conventional and microwave annealing

Ball-milling and subsequent conventional and microwave assisted heating processes have been applied to synthesize ZnNb₂O₆ nanoceramic. X-ray diffraction, simultaneous thermal analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and BET techniques were utilized to characterize the as-milled and annealed samples. Characterization of synthesized powders revealed that in spite of the very short heating time in the microwave process without soaking time, the powder heated at 550 °C had all physical properties similar to powders synthesized in conventional heating at the 650 °C temperature with a heating rate of 10 °C/min and a soaking time of 1 h. In addition, SEM, TEM and BET observations of synthesized powders showed that the particle size of powders lies in the nano meter range.     

The phase conversion of precursor powders for powder melting process YBa2Cu3O7−x superconductors

The effects of heating rate and holding time on the formation of YBa₂Cu₃O_7−x phase in precursor powders for YBa₂Cu₃O_7−x superconducting bulks prepared by powder melting process have been investigated. The phase conversion of the precursor powders is studied by X-ray diffraction and found to be different for different heating rates during heating. The YBa₂Cu₃O_7−x phase is formed during heating to peritectic temperature at 100 and 400 °C/h, but not at 6,000 °C/h. The longer the holding time, the more the amount of YBa₂Cu₃O_7−x phase between 880 °C and about 950 °C. The results are useful for understanding the mechanism of powder melting process and controlling the process conditions.     

A modified two-stage mixed oxide synthetic route to lead zirconate titanate powders

An approach to synthesis lead zirconate titanate [Pb(Zr_1−xTi_x)O₃; PZT] powders with a modified two-stage mixed oxide synthetic route has been developed. To ensure a single-phase perovskite formation, an intermediate phase of zirconium titanate (ZrTiO₄) was employed as starting precursor. The formation of perovskite phase in the calcined PZT powder has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. The morphology evolution was determined by scanning electron microscopy (SEM) technique. It has been found that the unreacted PbO and ZrTiO₄ phases tend to form together with PZT, with the latter appearing in both tetragonal and rhombohedral phases, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a 100% yield of PZT in a tetragonal phase.     

Improvement in synthesis of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> powders by Ge<Superscript>4+</Superscript> acceptor doping

In this paper, the effects of doping with GeO₂ on the synthesis temperature, phase structure and morphology of (K_0.5Na_0.5)NbO₃ (KNN) ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900°C for 2 h. Introducing 0.5 mol.% GeO₂ into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800°C, which can be ascribed to the formation of the liquid phase during the synthesis.     

Preparation and characterization of BaSnO<Subscript>3</Subscript> powders by hydrothermal synthesis from tin oxide hydrate gel

BaSnO₃ powders have been prepared from the tin oxide hydrate gel and the Ba(OH)₂ solution via hydrothermal synthesis route. The influence of the process parameters on the characteristics of BaSnO₃ has been studied. A powder with the single-phase of BaSnO₃ can be obtained only when the concentration of Ba(OH)₂ solution is no less than 0.2 M and the ratio of Ba:Sn lies between 1.0 and 1.2. At a hydrothermal temperature of 330 °C or higher, uniform BaSnO₃ powders can be directly prepared through hydrothermal reaction. When the hydrothermal temperature is lower than 250 °C, the as-prepared powder consists of BaSn(OH)₆ that transforms through an amorphous phase into BaSnO₃ by calcination at 260 °C. In the hydrothermal temperature range of 130–250 °C, a higher temperature can promote the crystallization of BaSnO₃, increases its specific surface area and decreases the average particle size. The duration of the hydrothermal reaction affects the morphology of the powder particles. The effects of the nonaqueous solvents on the properties of powders have also been investigated.     

Effect of CeO<Subscript>2</Subscript> on dielectric,ferroelectric and piezoelectric properties of PMN–PT (67/33) compositions

Lead magnesium niobate–lead titanate [Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃] powders doped with different mole % of CeO₂ were prepared by a modified columbite route with compositions corresponding to morphotropic phase boundary (MPB) region. These powders were calcined at 800 °C for 4 h and circular test specimens were prepared by uniaxial pressing. The specimens were sintered at 1150 °C/2 h, poled at 2 kV/mm d.c. voltage and were characterized for dielectric, ferroelectric and piezoelectric properties. It was observed that the piezoelectric and ferroelectric properties initially increase up to 2 mol% of ceria addition and then decrease with increase in ceria concentration. The diffusivity of the dielectric curves increases with increase in ceria concentration. The decrease in Curie temperature was observed from 173 °C corresponding to pure PMN–PT to a temperature of 138 °C for 10 mol% of ceria addition.     

The Effect of Sintering Temperature Variation on the Superconducting Properties of ErBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Superconductor Prepared via Coprecipitation Method

The effect of heat treatment on the superconducting properties of ErBa₂Cu₃O_7−δ (ErBCO) ceramic materials has been studied. The nano-metal oxalate precursor was prepared using coprecipitation (COP) method. The prepared materials were subjected to calcination process at 900 °C for 12 h and then sintered under oxygen environment for 15 h at 920 °C, 930 °C, 940 °C, and 950 °C, respectively. All samples showed a metallic behavior and single-step transition in the R–T curves. The best zero critical current, T _C(R=0)=91.4 K, was for the sample sintered at 920 °C. XRD data showed single phase of an orthorhombic structure. As the sintering temperature increases, the formation of nonsuperconducting phases (impurities) was observed when the samples sintered above 920 °C. The formation of nano-oxalate powders via COP method is a very efficient procedure to produce high-quality superconductors with less processing temperature required.     

Mechanochemical synthesis of BaTiO<Subscript>3</Subscript> from barium titanyl oxalate

The effect of mechanochemical processing in air and water on the physicochemical transformations of barium titanyl oxalate has been studied using X-ray diffraction, thermal analysis, FTIR spectroscopy, temperature-programmed argon desorption, and particle size measurements. The results demonstrate that mechanochemical processing of barium titanyl oxalate in air leads to the formation of structurally imperfect barium titanate. During subsequent air calcination at 550°C, this material transforms into well-crystallized cubic BaTiO₃, whereas thermal decomposition of barium titanyl oxalate only yields cubic BaTiO₃ starting at 800°C. Mechanochemical processing in water leads to partial amorphization of barium titanyl oxalate, and conversion of the product to BaTiO₃ requires heat treatment at 700°C. All of the BaTiO₃ samples obtained via mechanochemical processing have a larger specific surface in comparison with samples prepared by conventional calcination of barium titanyl oxalate or other known processes.     

Low temperature synthesis of MgTa2O6 powders

A combination of digestion and further low temperature calcination to crystallize the product is employed to prepare MgTa₂O₆ (MT) ceramics. Freshly prepared niobium hydroxide gel is mixed with magnesium hydroxide thoroughly and allowed to react at 100 °C under refluxing and stirring conditions for 6–12 h. The X-ray amorphous product so formed is heated at 550 °C to form crystalline MgTa₂O₆. This is the lowest temperature so far reported for the formation of MgTa₂O₆. For comparison, MT powders were also prepared by the traditional solid state method. Transmission electron microscope (TEM) investigations revealed that the average particle size is 40 nm for the low temperature calcined powders.     

Ceramic/natural rubber composites: influence types of rubber and ceramic materials on curing,mechanical, morphological,and dielectric properties

Influence of different types of rubber and ceramic material on cure characteristics, mechanical, morphological, and dielectric properties of natural rubber (NR) vulcanizate was studied. Two types of ferroelectric ceramic materials: barium titanate (BaTiO₃) and lead titanate (PbTiO₃) were prepared by solid-state reaction with calcinations at 1100 °C for 2 h. The ceramic powders were then characterized by X-ray diffraction (XRD), particle size analyzer, and SEM techniques. Ceramic/rubber composites were then prepared by melt mixing of rubber and ceramic powders. Two different types of NR (i.e., epoxidized NR [ENR] and unmodified NR) and two types of ceramic powders (i.e., BaTiO₃ and PbTiO₃) were exploited. It was found that incorporation of ceramic powders in rubber matrix and the presence of epoxirane rings in ENR molecules caused faster curing reaction, and higher delta torque but lower elongation at break. This is attributed to lower mobility of molecular chains and higher interaction between ENR molecules. Furthermore, SEM results revealed that the BaTiO₃ composites showed finer and better distribution of the particles in the rubber matrix than that of the PbTiO₃ composite. This caused superior mechanical properties of the BaTiO₃ composites. Furthermore, higher dielectric constant and loss tangent was observed in the ENR/BaTiO₃ composites.