Supamas Wirunchit

Physical properties and phase transitions in perovskite Pb[Zr1−x(Ni1/3Nb2/3)x]O3 (0.0 ⩽ x ⩽ 0.5) ceramics

A solid solution of lead zirconate–lead nickel niobate ceramics, Pb[Zr1−x(Ni1/3Nb2/3)x]O3 (PZNN) with x = 0.0–0.5, was synthesized via the columbite precursor method. The crystal structures as well as the thermal and dielectric properties were investigated in terms of the lead nickel niobate (PNN) concentration. X-ray diffraction indicated that all samples exhibited a single-phase perovskite structure. At room temperature, Pb[Zr1−x(Ni1/3Nb2/3)x]O3 is orthorhombic for a composition where x = 0, rhombohedral for the compositions where x = 0.1, 0.2 and 0.3 and pseudo-cubic for compositions where x = 0.4 and 0.5. The results of the addition of lead nickel niobate to the lead zirconate ceramic showed enhancement of the room-temperature dielectric permittivity. Lead nickel niobate substitution also led to lower transition temperatures. Furthermore, this transition from normal to relaxor FE ceramics was typified by a quasi-linear relationship between the diffuseness parameter δγ and the PNN mole fraction x.

Dielectric properties and phase transition behaviors in (1−x)PbZrO3–xPb(Mg1/2W1/2)O3 ceramics

The solid solution of lead zirconate [PbZrO3 (PZ)] and lead magnesium tungstate [Pb(Mg1/2W1/2)O3 (PMW)] has been synthesized by the wolframite precursor method. The crystal structure, phase transformations, dielectric and thermal properties of (1−x)PZ-xPMW, where x=0.00–0.10, were investigated. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. Phase-pure perovskite was obtained for all compositions. Furthermore, a change from orthorhombic to rhombohedral symmetry was observed as the mole fraction of increased PMW. As a result, it was found that PbZrO3–Pb(Mg1/2W1/2)O3 undergoes successive transitions from the antiferroelectric phase to the ferroelectric phase to the paraelectric state. The coexistence of orthorhombic and rhombohedral phases in this binary system is located near the composition x=0.1.

High temperature phases in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic

The phase evolution with temperature in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic was investigated with dielectric permittivity and polarization measurements, hot stage transmission electron microscopy, and high temperature x-ray diffraction. Below 190 °C, the ceramic is in the antiferroelectric phase with characteristic 14{110}c superlattice diffractions. In this stage, typical antiferroelectric 180° domains were observed. Between 190 and 220 °C, an intermediate phase, which is characterized by 12{110}c-type superlattice diffractions, was detected. Evidences are found to suggest that this intermediate phase is ferroelectric. The 12{110}c-type superlattice diffraction persists even into the paraelectric phase above 220 °C. In addition, there exists an incommensurate phase between the low temperature antiferroelectric phase and the intermediate ferroelectric phase.

Facile sonochemical synthesis of near spherical barium zirconate titanate (BaZr1−yTiyO3; BZT); perovskite stability and formation mechanism

The multicationic oxides of perovskite Ba(Zr,Ti)O3 were synthesized successfully by the sonochemical method without a calcination step. Detailed exploration considering the role of sodium hydroxide (NaOH) concentration, synthesis atmosphere, ultrasonic reaction time and precursor concentration on the perovskite phase formation and particle size was presented. It was found that nanocrystals were formed directly before being oriented and aggregated into large particles in aqueous solution under ultrasonic irradiation. The nucleation in the sonocrystallization process was accelerated by the implosive collapse of bubbles, while the crystal growth process was inhibited or delayed by shock waves and turbulent flow created by ultrasonic radiation. A pure complex perovskite phase of spherical shape was formed completely in a short irradiation time without the calcination process. Sonochemical irradiation could accelerate spherical shape formation of the particles significantly. These results provide new insights into the development and design of better nanomaterial synthesis methods.

Directed synthesis, growth process and optical properties of monodispersed CaWO4 microspheres via a sonochemical route

Monodispersed calcium tungstate (CaWO4) microspheres were synthesized successfully via a sonochemical process in deionized (DI) water. The functional group and phase formation analyses were carried out using Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. XRD revealed that all samples were of pure tetragonal scheelite structure. FT-IR and Raman analysis exhibited a W–O stretching peak of molecular [WO4]2−, which related to the scheelite structure. The effect of ultrasonic irradiation times in the sonochemical process was investigated briefly for 1, 5, 15 and 30 min. The shape of the particles was revealed as spherically monodispersed with narrow size distribution and uniform features at the ultrasonic time of 5 min. This study also found that the spherical surface was composed of tightly packed nanosphere subunits. A possible mechanism for the formation of CaWO4 powders with a different ultrasonic time was discussed in detail. Optical properties showed blue light emission at a wavelength of around 420 nm and an optical energy gap (Eg) value of 3.32–3.36 eV.

Preparation of Lead Zirconate-Lead Nickel Niobate Ceramics by the Reaction Sintering Process

The perovskite structure of lead zirconate – lead nickel niobate ceramics, (1-x) PbZrO 3 –xPb(Ni 1/3 Nb 2/3 )O 3 (PZ – PNN) at x between 0.00–0.50, has been prepared by the reaction-sintering process. The specimens were prepared directly from a mixture of their constituent oxide without any calcination step. The PZ – PNN ceramics could be obtained after 6 h sintering at 1,100–1,250°C. Crystal structure and phase transition of PZ-PNN were investigated by x-ray diffraction (XRD). XRD indicated that the structure of PZ-PNN ceramics is orthorhombic for a composition where x = 0.00, rhombohedral for compositions where x = 0.10 ≤ x ≤ 0.40 and pseudo-cubic for a composition where x = 0.50. The dielectric properties of the ceramics were measured as functions of both temperature and frequency. The results indicated that the transition temperature decreases with increasing PNN concentration. Furthermore, morphology and grain size evolution have been determined via a scanning electron microscope (SEM)

Crossover from Antiferroelectric to Normal Ferroelectric Behavior in Lead Zirconate—Lead Nickel Niobate Ceramics Prepared by the Reaction Sintering Process

The lead zirconate—lead nickel niobate ceramics, (1-x)PbZrO3—xPb(Ni1/3Nb2/3)O3 (PZ-PNN) with x = 0.00–0.10, have been prepared by reaction sintering. Without any calcination involved, the mixture of raw materials was pressed and sintered directly. The PZ–PNN ceramics could be obtained after 6 h sintering at 1,100–1,250°C. The crystal structure data obtained from XRD indicate that the PZ-PNN, where x = 0.00–0.10, successively transforms from orthorhombic to rhombohedral symmetry with an increase in the PNN concentration around x = 0.08. The antiferroelectric phase (AFE) → ferroelectric phase (FE) transition occurs in compositions of 0.0 ≤ x ≤ 0.08. The AFE → FE phase transition shifts to lower temperatures with higher compositions of x. The FE phase temperature range width increases with increased PNN.

The Effect of Zirconium on the Perovskite Phase Formation of Barium Zirconium Titanate Nanoparticles by the Sonochemical Method

The sonochemical technique is a powerful synthetic method for the production of nanostructured inorganic powders. Monosized spherical barium zirconium titanate [Ba(ZrxTi1-x)O3; BZT], with x = 0.00, 0.05, 0.20 and 0.40 nanoparticles, were synthesized successfully through sonochemical reaction. The phase formation as well as crystal structure and morphology were investigated. The as-prepared powders were identified by X-ray diffraction (XRD). The cubic perovskite structure of BZT was formed completely in a short irradiation time without the calcination process. The lattice parameter (a) of the samples increased with increasing zirconium concentration. Furthermore, when the concentration of zirconium increased, the reaction time must be increased in order to obtain phase-pure perovskite. The BZT nanoparticles showed a monosized spherical shape that was different from that in other preparation methods. The morphology of the products was very close to spherical, with the particle size distribution being rather narrow.

Nanocrystalline Barium Zirconium Titanate Synthesized by the Sonochemical Process

Nanocrystalline barium zirconium titanate, BaZr0.4Ti0.6O3, was synthesized successfully via the sonochemical process. The effects of reaction time on the precipitation of Ba(Zr,Ti)O3 particles were investigated briefly. The crystal structure as well as molecular vibrations and morphology were investigated. X-ray diffraction indicated that the powders exhibited a single phase perovskite structure, without the presence of pyrochlore or unwanted phases at the reaction time of 60 min. Nanocrystals were formed before being oriented and aggregated into large particles in aqueous solution under ultrasonic irradiation. A scanning electron microscopy (SEM) photograph showed the BZT powder as spherical in shape with uniform nanosized features.

Effect of Lead Nickel Niobate Substitution on Phase Transitions of Lead Zirconate Ceramics Prepared by the Solid State Reaction Method

The solid solution between the antiferroelectric, PbZrO3 (PZ), and relaxor ferroelectric, Pb(Ni1/3Nb2/3)O3 (PNN), was synthesized by the columbite method. The phase structure and phase transition of Pb(Zr1-x(Ni1/3Nb2/3)xO3 (PZNN), where x = 0.0 ≤ x ≤ 0.50, were investigated. The samples were kept at the calcination temperature of 900°C for 4 h and at the sintering temperature of 1,150°C for 2 h. Phase formation and phase transition of PZNN were investigated by x-ray diffraction (XRD) and thermal analysis, respectively. It was found that the structure of sintered pellets is orthorhombic for 0.0 ≤ x ≤ 0.10, rhombohedral for 0.20 ≤ x ≤ 0.30 and pseudo-cubic for x = 0.5. DSC measurement shows that in the antiferroelectric (AFE) phase – ferroelectric (FE) phase and FE to paraelectric (PE) phase; phase transformation temperatures decrease with increasing PNN concentration. The AFE–FE phase transformation was detected for compositions 0.00 £ x £ 0.08.