BaZrO3 Powders Research Articles

Interaction of liquid titanium with zirconates and titanates of some alkaline earth metals

Abstract The article presents the results of a study of the interaction of titanium melt with of zirconates BaZrO3 and SrZrO3, as well as titanate SrTiO3 under vacuum conditions and in an inert atmosphere at normal pressure. An original titanium heating method was used during the experiments. It eliminated the melt circulation at the interface between the solid and liquid phases. The method was based on resistive electrical heating of a Grade 2 titanium alloy rod or strip pressed into BaZrO3, SrZrO3 and SrTiO3 powders. Studied the structure, elemental, and phase composition of the products formed during various (up to 300 s) contact of titanium melt with surface zirconates and titaniums. The phase composition was compared with the products obtained by heating compacts from a mixture of titanium powders with BaZrO3, SrZrO3 and SrTiO3 powders. It was shown based on the results obtained that titanium, upon contact with these ceramic materials dissolves zirconium and oxygen and reduces barium and strontium to a metallic state. Barium and strontium evaporated due to the high vapor pressure at the experimental temperature, and caused the melt to splash or form a vapor layer that reduced the interaction rate of the melt with the ceramic. When a titanium melt interacted with BaZrO3 and SrZrO3 intermediate phases were not formed in quantities sufficient for their identification. The Sr3Zr2O7 phase was formed in small quantities during heating a mixture of Ti+SrZrO3 powders. When a titanium melt interacted with SrTiO3, a layer of an intermediate phase was formed, similar in composition to TiO2. Equations for the chemical reaction of the interaction of titanium with the indicated zirconates and titanate were compiled based on the experimental data obtained. It has been shown that titanium melt weted the surface of BaZrO3, SrZrO3 powders well and poorly weted the surface of SrTiO3 powder.

Chalcogenide perovskite BaZrS3 bulks for thermoelectric conversion with ultra-high carrier mobility and low thermal conductivity

Chalcogenide perovskites are expected to be promising thermoelectric materials, since they not only possess efficient carrier transport and defect tolerance, but also demonstrate unique advantages of high thermodynamic stability, eco-friendly and earth-abundant constituents. Especially, theoretical reports have predicted their “glass-like” thermal conductivities. However, experimental investigation on thermoelectric performances of chalcogenide perovskite BaZrS3 is extremely scarce due to the difficulty in preparing high-quality bulk samples, which originates from the brittle nature, high melting point, and the large difference in melting points between Ba/S and Zr. In this work, pure phase BaZrS3 bulks with high relative density reaching 100 % are realized by optimized sulfurization from low-cost BaZrO3 powders combined with fast spark plasma sintering. A maximum zT value of 0.37 at 623 K in BaZrS3 bulks is achieved, which is the record-high value among the reported sulfide, halide, and hybrid perovskite materials. A room-temperature electron mobility up to 385 cm2V−1s−1 is among the highest values for perovskites due to the high phase purity, dense morphology and corner-sharing ZrS6 octahedral three-dimensional network as effective carrier channels. Meanwhile, a measured low lattice thermal conductivity of 1.11 Wm−1K−1 at 623 K is attributed to the intense phonon scattering from the intrinsic distorted-perovskite structure and the lattice defects by sulfur deficiency. Moreover, the BaZrS3 bulks in this work are stable against moisture/air and high temperature test. This work provides new insights into the fundamental electrical and thermal properties of chalcogenide perovskites, and highlights their great potential in the practical thermoelectric applications.

Preparation of Tm3+ ion-doped BaZrO3 powder and its luminescence performance study

A series of Tm3+ ion doped BaZrO3 blue phosphors were synthesized by traditional hydrothermal method. The structure, morphology and luminescence properties of the synthesized materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectrum (FT-IR), size distribution and fluorescence spectrometer, respectively. The results show that the final products existed in a pure phase and with increasing of Tm3+ concentration, the grain size, lattice constants and lattice strain showed a trend of increase. In addition, by changing the supersaturation of the precursor solution, the spherical particle size can be carefully adjusted. When the doping molar fraction of Tm3+ was 5.0%, thebluemovementoftheinfrared absorption peakwasthemost, which was consistent with the theoretical calculations. Finally, based on the unique “probe” characteristics of Eu3+, it was confirmed that leading cause of energy level splitting was the reduction of the local symmetry of the matrix environment and the luminescence decrease should be attributed to the concentration quenching and lattice distortion.

(Ca,Sr,Ba)ZrO3: A promising entropy-stabilized ceramic for titanium alloys smelting

A novel entropy-stabilized (ES) (Ca,Sr,Ba)ZrO3 ceramic has been designed and synthesized by pressureless sintering of CaZrO3, SrZrO3 and BaZrO3 powders mixtures at 1450 °C, 1500 °C and 1550 °C for 3 h. X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550 °C. The relative density and hardness of the ES (Ca,Sr,Ba)ZrO3 ceramic sintered at 1550 °C are 97.79 % and 10.84 ± 0.33 GPa, respectively. This ES (Ca,Sr,Ba)ZrO3 exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates, CaZrO3, SrZrO3 and BaZrO3. Most importantly, the ES (Ca,Sr,Ba)ZrO3 ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES (Ca,Sr,Ba)ZrO3 ceramic in the contact region. The combination of these properties indicates that ES (Ca,Sr,Ba)ZrO3 ceramic is promising for use as a novel crucible material for the melting of titanium alloys.

Effect of YSZ with different Y2O3 contents on toughening behavior of Al2O3/Ba-β-Al2O3/ZrO2 composites

Al2O3 matrix composites containing in-situ formed monoclinic zirconia (m-ZrO2) and BaO·7.3Al2O3 (one of Ba-β-Al2O3 compounds) were prepared via reactive sintering of Al2O3 and BaZrO3 powders. When yttria-stabilized zirconia (YSZ) with Y2O3 contents of 1.5 mol% (1.5YSZ), 2 mol% (2YSZ), and 3 mol% (3YSZ) as well as Y2O3 particles were introduced into Al2O3 and BaZrO3 powder mixtures, the in-situ formed m-ZrO2 was stabilized, resulting from the migration of Y3+ from YSZ or Y2O3 to m-ZrO2 during sintering. The incorporation of YSZ contributed to the refinement of Al2O3 grains, whereas Y2O3-added samples showed larger grain sizes of Al2O3 matrix. The samples with YSZ or Y2O3 addition exhibited high fracture toughness, which is attributed to crack deflection/bridging and transformation toughening of ZrO2. Although the phase transformation is mainly derived from ZrO2 formed during sintering, 1.5YSZ particles added in the composites still showed much higher phase transformability compared to 2YSZ and 3YSZ particles.

Synthesis and characterization of BaZrO3 nanoparticles by citrate-nitrate sol-gel auto-combustion technique: Systematic study for the formation of dense BaZrO3 ceramics

Citrate-nitrate sol-gel auto-combustion method, employing high purity (≈99.999%) precursors, is adopted for the synthesis of BaZrO3 nanoparticles. TGA-DSC, PXRD, SEM, TEM and BET techniques are used to explain (1) thermolysis of gel, (2) optimization of thermal parameters for phase pure BaZrO3 nanoparticles of unimodal size-distribution and (3) microstructural evolution at the sintering stage. Complexation of citrates with cations in the gel is confirmed with the help of FTIR and solid-state MAS-13C-NMR spectrometry. Dried gel undergoes self-sustained combustion and finally resulted in white colour ashes. Ashes on further calcination at 1000 °C-8 h resulted in BaZrO3 powder with an average crystallite size of 69.5 nm, as calculated by microstrain-domain size analysis of XRD of BaZrO3 using Rietveld refinement. The crystallite size is consistent with SEM and TEM particle size analysis. The powder is sintered without any sintering-aid to achieve the highest density (99%) ever reported, compared to similar processes reported earlier.

Preparation of Ce4+-doped BaZrO3 by hydrothermal method and application in dual-frequent sonocatalytic degradation of norfloxacin in aqueous solution

In this paper, the dual-frequent sonocatalytic degradation of norfloxacin (NOR), an antibiotic, caused by Ce4+-doped BaZrO3 is studied. The used Ce4+-doped BaZrO3 as a novel sonocatalyst with highly efficient and stable sonocatalytic activity is prepared via hydrothermal method. The prepared sample is characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS) and Fourier transform infrared spectra (FT-IR) in order to investigate the structure, morphology and chemical composition. The dual-frequent sonocatalytic activity of prepared Ce4+-doped BaZrO3 powder is evaluated through sonocatalytic degradation of norfloxacin (NOR) as a model organic pollutant. Some influencing factors such as single/dual-frequent ultrasonic frequent, cerium and zirconium molar proportions, ultrasonic irradiation time and used times are studied in detail by using UV–vis spectra. The generated reactive oxygen species (ROS) during the dual-frequent sonocatalytic degradation process of norfloxacin (NOR) are confirmed by using two different trapping agents. The holes (h+) and hydroxyl radicals (OH) are identified and the holes plays a major role during the oxidation process. Finally, the possible mechanism for the dual-frequent sonocatalytic degradation of norfloxacin (NOR) caused by Ce4+-doped BaZrO3 is proposed. The experimental results show that the Ce4+-doped BaZrO3 displays a good sonocatalytic activity under dual-frequent ultrasonic irradiation. Under optimal conditions, the most of norfloxacin (NOR) can be removed under dual-frequent ultrasonic irradiation for 150 min.

Acceptor doping, hydration and band-gap engineering of BaZrO3

Yttrium-doped BaZrO3 powders have been synthesized by sol-gel method. Powder XRD confirms that BaZr1−xYxO3−δ (x = 0.00, 0.05, 0.10) crystallize with the perovskite-type unit cell (space group Pm3‾m). The effects of doping and hydration on the band gap of BaZr1−xYxO3−δ have been evaluated through the analysis of the diffuse reflection spectra. An additional absorption band is observed near the fundamental absorption edge in the doped samples annealed in dry oxygen. These findings are explained by the impact of defects on O(2p)–Zr(4d) charge transfer transitions and by trapping of electrons by oxygen vacancies.

Fabrication of Y2O3 doped BaZrO3 coating on Al2O3 applied to solidification of titanium alloy

The investment casting is one of the most versatile modern technique for metal forming, however, the high chemical stability of ceramic shell materials is required due to the high activity of titanium melt. The Al2O3 is one kind of the common refractory material, which can not be directly used for casting titanium alloys because of its reaction with the melt and contamination caused by this reaction. In this paper, the Y2O3 doped BaZrO3 coating was fabricated on the Al2O3 matrix in order to develop a novel casting and directional solidification technology. Using the Al2O3 as the matrix, the Y2O3 doped BaZrO3 coating was prepared by smearing the slurry, dusting the BaZrO3 powder and sintering them. The reaction between the Al2O3 matrix and the protective coating, the surface quality and chemical stability of the Y2O3 doped BaZrO3 coating were investigated using the optical microscope (OM), energy dispersive spectrometer (EDS) and scanning electronic microscope (SEM), respectively. Afterward, the interaction between Y2O3 doped BaZrO3 coating and titanium melt was discussed. Optical microscope and SEM results showed that the BaZrO3 coating possessed the good surface morphology and high chemical stability, and EDS results showed the thickness of interaction layer between the Al2O3 matrix and the protective coating did not vary with the sintering time and temperature (at 1500°C and 1600°C for 2, 4 and 6h). The thickness of diffusion layer was 10μm for the rod of Ti-46Al-8Nb with the directional solidification, the same was the counterpart for the casting part of Ti-6Al-4V alloy. This may imply that Y2O3 doped BaZrO3 is a promising coating for the solidification of titanium alloy.

Soft-mechanochemical synthesis of monodispersed BaZrO3 sub-microspheres: Phase formation and growth mechanism

Current technological and scientific challenges have encouraged the search for a simple and energy-efficient method to synthesis fine product particles with desirable morphology and properties. The submicro-spheres of perovskite barium zirconate (BaZrO3) in this study were synthesized successfully via the soft-mechanochemical method under ambient conditions, without surfactants or any capping agents. The synthetic mechanism model was proposed as being time-dependent. The hydrolysis, nucleation (crystallization) and growth of particles via Ostwald ripening were discussed deeply. Mechanical energy not only afforded a local high temperature to activate the chemical reaction and diffusion rate of particles, but also prevent aggregation and agglomeration by homogeneous mechanical stirring. Nevertheless, as-prepared BaZrO3 powders exhibited properties of photoluminescence (PL) with green emission from lattice formation defects. Dielectric properties and the quality factor (Q-factor) were investigated as well. It was notable that the soft-mechanochemical method can provide a high yield and enable work that is environmentally friendly.

High-temperature colossal dielectric behavior of BaZrO3ceramics

BaZrO3(BZO) powders were synthesized by solution combustion based on the glycine nitrate process.

Effect of Different Heating Process on the Photoluminescence Properties of Perovskite Eu-Doped BaZrO3 Powder

In this study, BaZrO3:Eu0.025 powder was synthesized through the solid-state reaction method with two different heating processes. For the one-step process, the BaZrO3:Eu0.025 powder was heated to 1000 °C–1400 °C for 2 h. For the two-step heating process, the BaZrO3:Eu0.025 powder was pre-heated at 800 °C for 2 h, after being cooled to room temperature and ground, then the powder was heated to 1000 °C–1400 °C again for 2 h. The optimum excitation optical wavelength of BaZrO3:Eu0.025 powders were 271 nm and the maximum intensity of the emission spectrum of BaZrO3:Eu0.025 powders increased with increasing heating temperature. The all-heated BaZrO3:Eu0.025 powders showed two strong orange emission bands peaking at the wavelengths of 574 and 596 nm and two weak emission bands peaking at 620 and 650 nm. As the heating temperatures were 1300 °C and 1400 °C, the maximum intensity of one-step heating BaZrO3:Eu0.025 powders appeared at the 5D0–7F0 (574 nm) and the maximum intensity of one-step heating BaZrO3:Eu0.025 powders appeared at the 5D0–7F1 (596 nm) transitions of Eu3+ ions, respectively.

Synthesis of nanosized BaZrO3 from oxalate precursor

Nanosized barium zirconate (BaZrO3) is prepared from its oxalate precursor, barium zirconyl oxalate (BZO). The decomposition of BZO precursor was studied by thermogravimetry, differential thermal analysis, fourier transform infra red spectroscopy (FTIR), and X-ray diffraction (XRD) techniques. FTIR and XRD study reveals that BZO precursor calcined at 1173 K for 2 h gives nanosized perovskite type cubic BaZrO3 powder. The transmission electron microscope study shows that BaZrO3 particles prepared at 1173 K is nearly spherical in shape with diameter of 40–75 nm. Particle size study was carried out to investigate particle size distribution of BaZrO3 particles. Band gap of BaZrO3 was estimated from UV–visible spectroscopy data. Impedance measurement study shows that dielectric constant of BaZrO3 prepared in this work is 31.69 at 10 kHz.

Water vapor-assisted solid-state reaction for the synthesis of nanocrystalline BaZrO<sub>3</sub> powder

Solid-state reaction between BaCO3 and ZrO2 is the simplest method to prepare BaZrO3, which is an important refractory structural material with a very high melting point and a low chemical reactivity. However, since the solid-state formation of the BaZrO3 phase requires high calcination temperature, this method typically produces larger particles unsuitable for the sintering process than the solution methods. In this study, we investigated the reaction behavior between very fine ZrO2 (70 nm) and coarse BaCO3 (1.5–5.7 µm) and described the water vapor-assisted solid-state synthesis of BaZrO3. Nanocrystalline BaZrO3 powder (~80 nm) was obtained by solid-state reaction at 1050°C in air. The BaZrO3 formation was accelerated by water vapor-assisted reaction. The apparent activation energy for the formation reaction was calculated to be 323 ± 21 kJ/mol and 263 ± 46 kJ/mol in air and humid air with H2O of 0.5 atm, respectively. In the 1 atm water vapor atmosphere, almost single-phase BaZrO3 was obtained by calcination at 750°C.

Photoluminescence properties of europium and titanium co-doped BaZrO3 phosphors powders synthesized by the solid-state reaction method

In this paper, we reported on the obtention of a series of europium and titanium co-doped BaZrO3 phosphors, which could emit red-orange long afterglow, synthesized by the solid-state reaction method. The structures, morphology and photoluminescent properties of the all samples were characterized and analyzed by X-ray diffraction (XRD), Schottky field-emission scanning electron microscope (FE-SEM), photoluminescence (PL) and decay curves, respectively. The XRD analyses showed that the reflection of all prepared BaZrO3 powders was well indexed to cubic structure. The room-temperature excitation spectra monitored at 594nm consist of a broad band with the stronger excitation PL peak, which located at 260nm, and a series of narrow bands. A series of narrow bands from 4f→4f emission transitions of the 5D0 excited level to the 7FJ (J=0–4) levels of the Eu3+ ions were observed in the emission spectra excited at 260nm. The decay curves of samples well coincided with the sum of two exponential functions. Combining experimental results and theoretical analyzis, we proposed a corresponding novel afterglow mechanism, which reasonably explained the afterglow phenomenon of BaZrO3:Eu, Ti. The BaZrO3:Eu, Ti phosphors had stronger afterglow, better monochromaticity and longer decay time compared with BaZrO3:Eu phosphors. It implied that the Ti co-doping was an effectual and practical way to improve afterglow performance of BaZrO3-based phosphors.

Preparation of Spherical Submicronic Barium Zirconate particles in Highly Basic Solution below 100°C

In this study, a new method has been developed to produce pure crystalline BaZrO3 powders from Ba+Zr solution or weakly soluble reactants by using precipitation route in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH−concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (∼80°C), after a short reaction time (15 minutes) and without requiring any precaution to avoid the presence of CO2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba+Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba+Zr] = 1 mol/l, reaction time = 15 minutes) yields a sub-micron precipitate.

Synthesis of BaZrO<sub>3</sub> Powders by Hydrothermal Method from Reactive Precursors

In this study, pure and crystalline BaZrO3 powders are prepared by hydrothermal synthesis using of precursor of barium chloride and zirconium oxychloride. The influence of several synthesis parameters is studied. At high OH- concentration, it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature. In addition, We had prepared high purity powder took a mere 1h at 130oC. The phase and particle morphology of the product were characterized by the techniques such as XRD, SEM and chemical analyses. The results indicated that the morphology of grain corresponded to rhombic dodecahedron, and the product had a particle size region which is 2~5µm.

Synthesis of Fine Micro-sized BaZrO3 Powders Based on a Decaoctahedron Shape by the Microwave-Assisted Hydrothermal Method

Micro-sized decaoctahedron BaZrO3 powders were synthesized by means of a hydrothermal microwave method at 140 °C for 40 min. The X-ray diffraction, Raman, UV−visible, and inductively coupled plasma atomic emission (ICP-AES) spectroscopy, as well as measurements of photoluminescence (PL) emission, were used for monitoring the formation of a perovskite phase with random polycrystalline distortion in the structure. Two emissions at 477 and 526 nm were accompanied by increase in the gap values, indicating the existence of different emission mechanisms. A theoretical model derived from previous first principle calculations allow us to discuss the origin of the photoluminescence emission in BaZrO3 powders which can be related to the local disorder in the network of both ZrO6 octahedral and dodecahedral (BaO12) hence forming the constituent polyhedron of BaZrO3 system. Initial observations of a novel morphology of the BaZrO3 perovskite crystal growth based on decaoctahedron shape is demonstrated and indirectly r...

Intense blue and green photoluminescence emissions at room temperature in barium zirconate powders

Intense blue and green photoluminescence (PL) emissions were observed at room temperature in barium zirconate (BaZrO3) powders prepared by chemical method. The powders were analyzed by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption spectroscopy (EXAFS) and ultraviolet–visible (UV–vis) absorption spectroscopy. The XRD patterns indicated the presence of a secondary phase of BaCO3 in BaZrO3 powders heat treated at 773 K. K-edge XANES data revealed that Zr atoms presents in at least two Zr environments. EXAFS investigations showed strong bond length dispersion in the first coordination shell around Zr atoms. EXAFS analysis indicated that Zr atoms are coordinated by 6 oxygen in BaZrO3 powders heat treated at 973 K. UV–vis measurements suggested the presence of intermediary energy levels into the band gap of BaZrO3 powders heat treated at 773 K. The intense PL emission in BaZrO3 powders can be attributed to the two Zr environments or ZrO5–ZrO6 clusters. © 2008 Elsevier B.V. All rights reserved.

Experimental and theoretical correlation of very intense visible green photoluminescence in BaZrO3 powders

Very intense visible green photoluminescence (PL) was observed at room temperature in structurally ordered-disordered BaZrO3 powders. Ab initio calculations, ultraviolet-visible absorption spectroscopy, electron paramagnetic resonance, and PL were performed. Theoretical and experimental results showed that local defects in the cubic structure caused by [ZrO5⋅VOz] complex clusters, where VOz=VOx, VO•, and VO••, play an important role in the formation of hole-electron pairs, giving rise to a charge gradient in the structure which is responsible for PL emission.