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.     

Effect of calcination conditions on phase formation and particle size of nickel niobate powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb₂O₆) powders. The formation of the NiNb₂O₆ 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 the minor phases of unreacted NiO and Nb₂O₅ precursors and the Ni₄Nb₂O₉ phase tend to form together with the columbite NiNb₂O₆ phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb₂O₆ in an orthorhombic phase.     

Effect of calcination condition on phase formation and particle size of lead titanate powders synthesized by the solid-state reaction

A perovskite-like phase of lead titanate, PbTiO₃, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. Phase formation of the calcined powders has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by DTA and X-ray diffraction (XRD) techniques. Moreover, morphology and particle size evolution have been determined via SEM technique, respectively. It has been found that single-phase PbTiO₃ powders were successfully obtained for calcination conditions of 550 °C for 4 h or 600 °C for 1 h with heating/cooling rates of 20 °C/min. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates.     

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.     

Effect of vibro-milling time on phase formation and particle size of nickel niobate nanopowders

A columbite-type phase of nickel niobate, NiNb₂O₆, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of NiNb₂O₆ powder was investigated. Powder samples were characterized using DTA, XRD, SEM and laser diffraction techniques. It was found that the smallest particle size of 32 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 35 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

Effect of calcination conditions on phase formation and particle size of lead nickel niobate powders synthesized by using Ni4Nb2O9 precursor

An approach to synthesize lead nickel niobate, Pb(Ni_1/3Nb_2/3)O₃ or PNN, powders with a modified two-stage mixed oxide synthetic route has been developed. Novel intermediate phase of nickel diniobate (Ni₄Nb₂O₉) was employed as a B-site precursor, with the formation of the PNN phase 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 the unreacted PbO and Pb_1.45Nb₂O_6.26 phases tend to form together with PNN, depending on calcination conditions. It is seen that optimization of calcination conditions can lead to a 100% yield of PNN in a cubic phase.     

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.     

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.     

Effect of calcination conditions on phase formation and particle size of Zn3Nb2O8 powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase Zn₃Nb₂O₈ powders. The formation of the Zn₃Nb₂O₈ 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 the minor phases of unreacted ZnO and Nb₂O₅ precursors and the columbite ZnNb₂O₆ phase tend to form together with the Zn₃Nb₂O₈ phase, depending on calcination conditions. It is seen that optimization of calcination conditions can lead to a single-phase Zn₃Nb₂O₈ in a monoclinic phase.     

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.     

Effect of vibro-milling time on phase formation and particle size of lead zirconate nanopowders

A perovskite phase of lead zirconate, PbZrO₃, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of PbZrO₃ powder was investigated. Powder samples were characterized using TG-DTA, XRD, SEM and laser diffraction techniques. It was found that an average particle size of 50 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed upon continuation of milling to 35 h. In addition, by employing an appropriate choice of milling time, a narrow particle size distribution curve was also observed.     

Effect of calcining temperature on particle size of hydroxyapatite synthesized by solid-state reaction at room temperature

Using diammonium phosphate, calcium nitrate tetrahydrate and sodium bicarbonate as raw materials, hydroxyapatite (HAP) was facilely synthesized by solid-state reaction at room temperature. The crystallinity, phase, morphology and particle size of the products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry/differential thermal analysis (TG–DTA) and particle size analyzer. The influence of calcining temperature on the crystallinity and composition of HAP phase was also investigated.     

Dielectric properties of lead indium niobate ceramics synthesized by conventional solid state reaction method

Pyrochlore free lead indium niobate ceramics are successfully prepared using wolframite precursor by conventional solid state reaction method in air atmosphere, by adding an excess amount of MgO in PbO-InNbO₄ mixture. The dielectric properties of lead indium niobate ceramic studied as a function of both temperature and frequency indicate relaxor ferroelectric behavior with maximum dielectric constant of 4310 at 40 ^οC for 1 kHz. Lowering of transition temperature and enhancement of dielectric constant at room temperature, compared to earlier reports, may be due to the diffusion of magnesium ion into the lead indium niobate. The saturation polarization P_s, measured at room temperature, is found to be 22.5 μC/cm² for 40 kV/cm.     

Structural and dielectrical studies on mechano-chemically synthesized indium doped CdS nanopowders

Incorporation of indium (dopant) into CdS crystals have been successfully achieved by a mechanical alloying process. Powders are prepared with various In/Cd ratio from 1 to 10 at% and milled at 300 revolution per minute (rpm) for 60 min. X-ray diffraction (XRD) analysis of milled In doped CdS compound showed that the major phase of the product was wurtzite with grain sizes varying from 37 to 42 nm corresponding to change in In/Cd compositions. High resolution transmission electron microscopy (HRTEM) images as well as Fourier transformation in reciprocal space provide a good pathway to identify the structure of individual CdS nanocrystals, whose dominant phase was determined to be wurtzite structure along with zinc blende structure. Field emission scanning electron microscopy (FESEM) images reveal that CdS crystal prefers to grow along the (001) direction rather than (110) due to its high surface energy. The Raman spectra of CdS:In particles present well-resolved lines at approximately 303 and 600 cm⁻¹, corresponding to the first and second-order scatterings, respectively, of the longitudinal optical (LO) phonon mode. Dielectrical studies showed that dielectrical constant (ε′) decreased with increase in frequency, whereas AC conductivity (σ_AC) in In doped CdS increases with increase in frequency and also both the values increased with increase in doping concentration.     

Effects of vibro-milling time on phase formation and particle size of Zn3Nb2O8 nanopowders

A monoclinic phase of zinc niobate, Zn₃Nb₂O₈, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of Zn₃Nb₂O₈ powder was investigated. The formation of the Zn₃Nb₂O₈ phase in the calcined powders has been investigated using DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and laser diffraction techniques. It was found that an average particle size was achieved at 20 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 30 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

固相研磨-低温煅烧法制备钛酸钡纳米粉体

以氢氧化钡和钛酸丁酯为原料,采用固相研磨与低温(200～300℃)煅烧相结合的方法制得了钛酸钡纳米粉体.用XRD、TEM、IR和ICP对产品进行了表征;并用TG-DTA对纳米粉体的形成过程进行了分析.结果表明,所得钛酸钡纳米粉体的粒径约为15～20nm,粒子形状近似为球形,晶体结构为立方相,钡钛物质的量之比约为1.0.该粉体在热外理温度为800～1000℃时,由立方相转变为四方相;而在热外理温度为668～892℃时,存在于晶格中的羟基被除去.     

Effect of temperature schedule on the particle size of barium titanate during solid-state reaction

Nano-sized BaTiO₃ particles were synthesized by a solid-state reaction in air using a 2-step heat treatment process. The dependence of the particle size and tetragonality (=c/a) on the temperature schedule was investigated. The temperature was held for 10 h at an intermediate temperature before heating to the target temperature of 1000°C for 1 h. Although more heat was consumed, the powders synthesized by the 2-step heat treatment method showed a much smaller particle size with higher tetragonality than those produced by direct heating. For example, the mean particle size was <100 nm at a holding temperature ranging from 500-700 °C, while it was 246 nm for direct heating to the same target temperature of 1000 °C. This was explained by the enhanced nucleation rate during temperature holding stage based on the TG/DTA and high temperature XRD results.     

Effect of hydrogen annealing on the composition and particle size of molybdenum nanopowders

We have studied the behavior of molybdenum nanopowder consisting of particles with an average size of 23.7 nm. The powder was prepared by hydrogen plasma reduction of molybdenum trioxide and contained considerable amounts of oxygen in the form of amorphous molybdenum oxides and hydroxides. Annealing in hydrogen for 1 h at temperatures from 300 to 1000°C is shown to cause crystallization of oxides, which then vaporize to form the volatile hydroxide MoO₂(OH)₂. Most of the oxygen is removed by annealing below 700°C. Starting at this temperature, particle growth is observed. The main mechanism behind the coagulation of molybdenum particles is vapor transport. Annealing at 1000°C for 30–50 min in hydrogen with a dew point of −5°C increases the particle size by about one order of magnitude.     

Autosegregation and phase formation on the surface of calcium niobate crystals

Nanoscale changes in the surface morphology and elemental composition of calcium niobate, Ca₂Nb₂O₇, crystals in response to thermally stimulated surface autosegregation have been studied for the first time. The results demonstrate that, depending on annealing temperature and duration, the calcium niobate surface becomes niobium-enriched. This is accompanied by the formation of surface phases identical in composition to the host crystal. At 770 K, the surface phase consists of oriented nanocrystallites. With increasing annealing temperature and duration, the nanocrystallites transform into partially oriented microcrystallites identical in composition to the host crystal. Annealing at 1270 K, that is, well below the melting point of Ca₂Nb₂O₇ (1873 K) leads to disproportionation of the surface phase and formation of both niobium-enriched and niobium-deficient phases, including pure CaO. The high-temperature surface phases consist of individual crystallites and intergrowths, which form layers with a rather large surface coverage.     

Synthesis of potassium niobate (KNbO3) nano-powder by a modified solid-state reaction

Crystalline lead-free piezoelectric potassium niobate (KNbO₃) powders have been synthesized through a modified solid-state reaction method. The thermal behavior of the K₂C₂O₄·H₂O and Nb₂O₅ raw material mixture was investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The X-ray diffraction technique (XRD) was used to investigate the phase formation and purity. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern showed that the monophasic perovskite phase of KNbO₃ could be synthesized successfully at a temperature as low as 550 °C for 240 min, with an average crystallite size of 36 ± 8 nm. The SEM images suggested that the average particle size of the powder obtained was 278 ± 75 nm.