O. Khamman

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

Abstract The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb 2 O 6 ) powders. The formation of the NiNb 2 O 6 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 Nb 2 O 5 precursors and the Ni 4 Nb 2 O 9 phase tend to form together with the columbite NiNb 2 O 6 phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb 2 O 6 in an orthorhombic phase.

EFFECT OF NICKEL NIOBATE B-SITE PRECURSORS ON PHASE FORMATION, MICROSTRUCTURE AND DIELECTRIC PROPERTIES OF PEROVSKITE PNN CERAMICS

Relaxor perovskite lead nickel niobate (PNN) ceramics were fabricated by using B-site precursor method, in which both columbite-NiNb2O6 and corundum-Ni4Nb2O9 were separately employed as nickel niobate B-site precursors. It has been found that optimization of sintering condition can successfully lead to highly dense and pure PNN ceramics in both routes. Between the two B-site precursor routes, pure perovskite PNN ceramics with slightly better densification and dielectric properties can be produced by using the columbite-route.

A Two-Stage Solid-State Reaction to Lead Zirconate Titanate Powders

An approach to synthesize lead zirconate titanate (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 lead zirconate (PbZrO 3 ) was employed as starting precursor. The formation of perovskite phase in the calcined powders has been investigated as a function of calcination temperature. It has been found that the perovskite PbZrO 3 and PbTiO 3 phases tend to form together with PZT, with the latter appearing in both tetragonal and rhombohedral phases, depending on calcination temperatures. It is seen that optimization of calcination can lead to 100% yield of PZT phase.

XPS characterization of perovskite relaxor PNN ceramics prepared by corundum precursor method

Perovskite ferroelectric PNN ceramics have been obtained from oxides by sintering in air, using a two-stage process with corundum Ni4Nb2O9 precursor. Under suitable firing condition, XRD analysis revealed that the ceramics consist of 100% perovskite phase. The SEM, EDX, and XPS techniques were employed to investigate the chemical composition of the surfaces of the PNN ceramics. Fluctuation in chemical composition, precipitation of NiO and the Pb-Ni-Nb-O phase different from perovskite were found.

Fabrication, phase formation and microstructure of Ni4Nb2O9 ceramics by using two-stage sintering technique

The potential utilization of two-stage sintering for the production of very dense and pure nickel diniobate (Ni4Nb2O9) ceramics with low firing temperature was demonstrated. The effects of the designed sintering conditions on the phase formation, densification and microstructure of the ceramics were characterized by using X-ray diffraction (XRD), Archimedes method and scanning electron microscopy (SEM), respectively. The minor phase of columbite NiNb2O6 tended to form together with the desired Ni4Nb2O9 phase, depending on the sintering conditions. Optimization of the sintering conditions may lead to a single-phase Ni4Nb2O9 ceramics with an orthorhombic structure. The ceramics doubly sintered at 950/1250 ◦C for 4 h exhibited a maximum density of ~92%. Microstructures with denser angular grain-packing were generally found in the sintered Ni4Nb2O9 ceramics. However, the grains were irregular in shape when the samples were sintered at 1050/1250 ◦C. Two-stage sintering was also found to enhance the ferroelectric behavior of the Ni4Nb2O9 ceramic.

Fabrication, phase formation and microstructure of Ni4Nb2O9 ceramics fabricated by using the two-stage sintering technique

The potential utilization of two-stage sintering for the production of very dense and pure nickel diniobate (Ni4Nb2O9) ceramics with low firing temperature was demonstrated. The effects of the designed sintering conditions on the phase formation, densification and microstructure of the ceramics were characterized by using X-ray diffraction (XRD), Archimedes method and scanning electron microscopy (SEM), respectively. The minor phase of columbite NiNb2O6 tended to form together with the desired Ni4Nb2O9 phase, depending on the sintering conditions. Optimization of the sintering conditions may lead to a single-phase Ni4Nb2O9 ceramics with an orthorhombic structure. The ceramics doubly sintered at 950/1250 ◦C for 4 h exhibited a maximum density of ~92%. Microstructures with denser angular grain-packing were generally found in the sintered Ni4Nb2O9 ceramics. However, the grains were irregular in shape when the samples were sintered at 1050/1250 ◦C. Two-stage sintering was also found to enhance the ferroelectric behavior of the Ni4Nb2O9 ceramic.

Phase Formation and Dielectric Properties of Ge Doped (Bi0.5Na0.5)TiO3 Ceramics

Ge doped (Bi0.5Na0.5)TiO3 ceramics, (Bi0.5Na0.5)Ti1-x Ge x O3 (BNTG, x = 0, 0.05, 0.10, 0.15 and 0.2), were prepared by using a solid-state method. The crystal structure of the ceramics was investigated by X-ray diffraction method. It was found that, under suitable conditions, all compositions can form single perovskite phase with rhombohedral symmetry. The grain size and morphology of the ceramics were examined by SEM. The average grain size of the ceramics was found to decrease with increasing Ge content. The dielectric constant was measured as a function of both temperature and frequency. All samples exhibited a relaxor ferroelectric behavior.

Sintering Properties and Microstructure of NiMn2O4-Silver Composites

Sintering properties, phase and microstructure of nickel mangante-silver composites were studied. Nickel manganite (NiMn2O4) powder, synthesized by solid state coordination, was mixed with silver particles by ball milling for 21 h. NiMn2O4-xAg (when x = 0, 3, 6, 9, 12 and 15 wt%) ceramic composites with pellet diameter of 1 cm were fabricated by uniaxial pressing (1 ton) and subsequent cold isostatic pressing (170 MPa) and then sintered at 1200°C for 3 h. NiMn2O4 ceramics have 97% relatively density. It was found that some Ag particles may evaporate from the surface of NiMn2O4-xAg composites. Decreasing of shrinkage as Ag content increases may be due to porosity occurred by Ag evaporation at high temperature and coalescence of Ag agglomerated particles. No chemical reaction between NiMn2O4 and Ag particle was observed by X-ray diffraction. Dispersion of Ag particles in NiMn2O4 matrix was revealed. It is found that Ag particles agglomerate into larger size particles when the amount of Ag increases. Resistivity at room temperature of NiMn2O4 is dramatically decreases by 3 wt%Ag addition.

DIELECTRIC PROPERTIES OF COMPLEX PEROVSKITE PZBT-PMNT CERAMIC UNDER COMPRESSIVE STRESS

Effects of compressive stress on the dielectric properties of complex perovskite PZBT-PMNT ceramic were investigated. The dielectric properties measured under stress-free condition showed a composite nature with two distinct temperatures of dielectric maximum associated with PZBT and PMNT end members. The dielectric properties under the compressive stress were observed at stress levels up to 230 MPa using a home-built compressometer. The results clearly showed that the compression load significantly reduced both the dielectric constant and the dielectric loss tangent in every measuring frequency. The change of the dielectric constant with stress was attributed to competing influences of the intrinsic contribution of non-polar matrix and the extrinsic contributions of re-polarization and growth of micro-polar regions, while the clamping of the domain walls contributed to the stress-dependent changes of the dielectric loss tangent. Finally, a large drop of the dielectric constant after a stress cycle was likely caused by the stress induced decrease in switchable part of spontaneous polarization.

Effects of Vibro-Milling Time and Calcination on Phase Formation and Particle Size of Lead Zirconate Nanopowders

Effect of calcination conditions on phase formation and particle size of lead zirconate (PbZrO 3 ) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. It was found that the calcination time for the formation of pure PbZrO 3 was lower when longer milling times were applied. More importantly, by employing an appropriate choice of the milling time and calcination conditions, PbZrO 3 nanopowders have been successfully prepared with a simple solid-state reaction method.