Tetragonal Phase Transformation Research Articles

Cubic to pseudo-cubic tetragonal phase transformation with lithium and beryllium doping in CaTiO3 and its impact on electronic and optical properties: a DFT approach

First-principles calculations, with CASTEP code, were employed to study the effect of lithium (Li) and beryllium (Be) doping on structural stability, phase transformation, electronic band structure and optical characteristics of CaTiO3. The substitution of Ca-atoms with the Li- and Be-atoms changes the lattice parameters and hence unit cell volume and consequently the electronic band structure of CaTiO3 is modified. With 12.5% Li- and Be-doping, we observed a structural phase transformation from cubic to pseudo-cubic tetragonal structure which is in good agreement with the literature. The impact of structural phase transformation on the electronic band structure has been explained with the help of total, partial and elemental partial density of states. In case of Li-doping, the value of band gap slightly increases from 1.866 to 1.964 eV while the band gap value decreases to 1.614 eV for Be-doping. In both cases of doping, maxima of valence band are shifted from R to Z symmetry point whereas the minima of conduction band remain at G symmetry point. In pure and doped cases, the nature of the band gap remains unaltered, i.e., indirect band gap. From optical response of the doped compounds, we perceive a red shift in the absorption. With Be- and Li-doping, the static refractive index also increased from 2.48 to 2.63 and 4.1, respectively. The change in electronic structure and optical characteristic with Li- and Be-doping would make this compound a suitable candidate for future optoelectronic devices.

Oxidation induced cubic-tetragonal phase transformation in titanium hydride powders

We studied the effect of oxidation temperature and initial hydrogen concentration on the occurrence of cubic (δ) to tetragonal (ε) phase transformation induced by thermal oxidation of titanium hydride powders in air. X-ray diffraction analysis indicates that δ → ε transformation occurs during oxidation at 400 °C, but not at lower (300 °C) or higher (500 °C) oxidation temperatures. The relative amounts of hydrogen loss during oxidation were determined by temperature-programmed desorption mass spectrometry (TPD-MS). The findings suggest that oxygen stabilizes the tetragonal phase (ε), and that the δ/ε phase composition following oxidation depends on both oxygen and hydrogen concentrations. For high oxidation temperatures (500 °C), some degree of hydride decomposition leads to a decrease in H concentration and to destabilization of the tetragonal phase after cooling down to room temperature.

Effects of interfacial stress in phase field approach for martensitic phase transformation in NiAl shape memory alloys

A phase field approach for phase transition between austenite to martensitic variants and twinning between martensitic variants is presented with the main focus on the effects of interfacial stress on phase transformations. In this theory, each variant-variant phase transformations and twinnings within each martensitic variant can be represented by only one-order parameter. Thus, it allows us to get the analytical solution of the martensite-martensite interface profile, energy, and width. Moreover, this model allows us to include interface stress which is consistent with the sharp interface limit. The finite element method is utilized to solve the coupled phase field and elasticity equations for a cubic to tetragonal phase transformation in NiAl shape memory alloy. The stress fields are obtained and the effects of interfacial stress on the stress field at the interfaces are studied for both austenite–martensite and martensite–martensite interfaces in detail. Additionally, the temperature-induced growth of the martensitic phase inside austenite, martensitic phase transformation, and twining are solved. The evolution of the microstructure and stress fields are obtained and the effects of interfacial stress on the morphological evolution of martensitic nanostructures are examined. It is found that the interfacial stress is an important factor, influencing the stress distribution at interfaces and the phase field solution significantly. This theory can be extended for electric, reconstructive, and magnetic phase transformations.

High recoverable energy storage density and large energy efficiency simultaneously achieved in BaTiO3–Bi(Zn1/2Zr1/2)O3 relaxor ferroelectrics

Relaxor ferroelectrics have attracted much attention as electric energy storage materials for intermittent energy storage because of their high saturated polarization, near-zero remnant polarizations, and considerable dielectric breakdown strength (BDS). Despite the numerous efforts, the dielectric energy storage performance of relaxor ferroelectric ceramics is incomplete or unsatisfactory. The enhancement of recoverable energy storage density Wrec usually accompanies with the sacrifice of discharge-to-charge energy efficiency η; therefore, it is an important issue to achieve high recoverable Wrec and large efficiency η simultaneously. In this work, the (1-x)BaTiO3-xBi(Zn1/2Zr1/2)O3 (abbreviated as BT-100xBZZ, 0 ≤ x ≤ 0.20) ferroelectric ceramics were prepared using the conventional solid-state reaction method. The phase structure, microstructural morphology, dielectric and ferroelectric properties, relaxation behaviors, and energy storage properties of BT-BZZ ceramics were investigated in detail. X-ray powder diffraction, dielectric spectra, and ferroelectric properties confirm the transformation of tetragonal phase for normal ferroelectrics (BT) to pseudo-cubic phase for relaxor ferroelectrics (BT-8BZZ). A high recoverable energy storage density Wrec of 2.47 J/cm3 and a large energy efficiency η of 94.4% are simultaneously achieved in the composition of BT-12BZZ, which presents typical weakly coupled relaxor ferroelectric characteristics, with an activation energy Ea of 0.21 eV and a freezing temperature Tf of 139.7 K. Such excellent energy storage performance suggests that relaxor ferroelectric BT-12BZZ ceramics are promising dielectric energy storage materials for high-power pulsed capacitors.

Effect of A Rapid-Cooling Protocol on the Optical and Mechanical Properties of Dental Monolithic Zirconia Containing 3-5 mol% Y2O3.

Many attempts have been made to improve the translucency of zirconia in dentistry. The purpose of this study was to evaluate the effect of a rapid-cooling heat treatment on the optical and mechanical properties of dental monolithic zirconia. Zirconia containing 3, 4, and 5 mol% Y2O3 were sintered, sectioned, and polished. The specimens were rapidly cooled from high temperature inducing a diffusionless cubic-to-metastable tetragonal (t’) phase transformation. The changes in L*a*b* color coordinates, translucency parameter (TP), and total transmittance (T%) were measured. Three-point bending strength, Vickers hardness, and indentation fracture toughness tests were performed. Quantitative phase analyses were carried out by X-ray diffraction with Rietveld refinement. Scanning electron microscopy (SEM) images were obtained. With increasing Y2O3 contents, TP and T% values increased while strength and toughness decreased. The Rietveld analysis showed that the amount of t’-phase increased after rapid-cooling and annealed 5Y-partially stabilized zirconia (PSZ) contained the highest amount of t’-phase (64.4 wt%). Rapid-cooling improved translucency but the translucency of annealed 5Y-PSZ did not approach that of lithium disilicate glass-ceramic. Rapid-cooling decreased flexural strength significantly, being 306.1 ± 61.8 MPa for annealed 5Y-PSZ. SEM revealed that grains tended to get larger after rapid-cooling. A rapid-cooling treatment can produce t’-phase which can contribute to an increase in translucency but has a negative effect on the mechanical properties of zirconia.

Structural configuration and tetragonal phase stability in the equiatomic quaternary Heusler compound TiZnMnSi.

Heusler materials have aroused great scientific research interest during recent years due to their special electronic and magnetic properties. Especially for the equiatomic quaternary Heusler compounds, they exhibit very high composition flexibility and structure tunability. In this work, we have carried out a systematic study on the structural configuration and tetragonal stability for the Heusler compound TiZnMnSi by first-principles calculations. Results reveal the type-A structure with ferromagnetic state possesses the lowest total energy and thus should be the ground state configuration. Based on the equilibrium lattice constant, the electronic band structures and magnetic moments have been computed. The tetragonal phase transformation is then investigated by using the total energy variation under different tetragonal strains, and the stability analysis of the mechanical and dynamic properties indicates that TiZnMnSi exhibits a strong tendency for the tetragonal phase. These findings could provide reference data for relative experiments as well as a very helpful theoretical reference for this fascinating class of materials.

Comparative In Vitro Evaluation Between Zirconia and Veneer Ceramic Materials Using Different Techniques

Zirconia surface treatment using different techniques could be employed to overcome the delamination issue reported between veneering ceramic materials and the corresponding zirconia core. The study subjected yttria partially stabilized zirconia core material to grinding and sandblasting as a first surface treatment. An airbrush gun spraying technique was used to coat a uniform thin layer of veneering ceramic (IPS e.max Ceram and Noritake Cerabien ZR) on the core materials followed by performing laser scanning as a second surface treatment. The specimens were investigated for surface topography, interface analysis, elemental compositions, phase transformation, and fracture mode patterns using profilometer, SEM, EDS, XRD, and stereomicroscope. The impact of laser scanning on the shear bond strength before and after storage of specimens in artificial saliva was also studied. Transformable tetragonal phase to monoclinic was predominant in sandblasted specimens followed by laser scanning with observation of micro-cracks at interface. The grinding followed by laser scanning yielded satisfactory outcomes in terms of the presence of coating property. The phase transformation was not detected through the latter technique. The technique greatly enhanced the roughness property and bond strength values which might be considered as a reliable application to improve the longevity of fixed dental crowns in load bearing areas.

The effect of titania doping on structure and mechanical properties of calcia-stabilized zirconia ceramic

The effect of titania doping on density, phase composition, and mechanical properties of calcia-stabilized tetragonal zirconia ceramics (Ca-TZP) was investigated. The samples were prepared via milling, spray drying and consequent uniaxial pressing of the powders of the chosen composition. The concentrations of titania of up 1 mol% were investigated. Addition of titania moderately improved relative density of the sintered ceramics from 98.2% in titania-free material to 99.3% in 0.5 mol% titania ceramic. Introduction of titania resulted in increase of transformability of tetragonal zirconia phase deduced from the change of lattice parameters and content of monoclinic zirconia phase on fracture surfaces. It was revealed that hardness of titania-doped Ca-TZP decreased from 12.2 GPa in undoped ceramic to 11.3 GPa in material with 0.75 mol% titania. Fracture toughness, on the contrary, demonstrated a clear extremum of 9.1 MPa·m0.5 in 0.5–0.65 mol% titania range as compared to ∼5 MPa·m 0.5 in undoped Ca-TZP.

Phase transformation and modifications in high-k ZrO2 nanocrystalline thin films by low energy Kr5+ ion beam irradiation

In present communication, zirconium oxide (ZrO2) thin films of thickness (155 nm) were grown by using RF sputtering technique. To address and systematically understand the effects of low energy (800 keV) irradiation, high-k ZrO2 thin films were irradiated at room temperature by Kr ions with a range of fluence 1E15 to 1E17 ions. cm−2. The polymorphous zirconia pristine and irradiated thin films were characterized through X-ray diffraction (XRD) technique which confirms the coexistence of monoclinic and tetragonal phases. Monoclinic to tetragonal structural phase transformation was observed for Kr5+ ions irradiated samples at a fluence of 5E15, 1E16, 1E17 ions. cm−2. All samples were characterized by UV–Vis spectroscopy to study the mechanism of variation in optical energy band gap (4.42–4.52 eV), Urbach energy (402–449 meV) and refractive index (1.518–1.523) with increasing ion fluence. Photoluminescence (PL) spectroscopy was done at room temperature to record the significant PL broad prominent emission peaks at 350 nm and 430 nm and the peak intensity of these peaks significantly varies due to the annihilation of primary defects or generation of new defects centres by the influence of Kr ion irradiation. To determine the significant variation in grain size (50–85 nm) and RMS surface roughness (0.54–1.04 nm), pristine and irradiated sample were characterized by atomic force microscopy (AFM). A complete mechanism of the evolution of surface roughness was analyzed by determining the power spectral density (PSD). Further surface roughness component in the range of 0.4–1.7 was calculated using the slope of the tail of PSD. The FTIR spectra of pristine and low energy ion irradiated ZrO2 thin films were recorded in the range of 1250–3200 cm−1. The Rutherford backscattering spectrometry (RBS) was carried out in channeling condition and the experimental results were simulated to evaluate the elemental composition of Zr and O (⁓1:2) and film thickness (155 nm) of the samples. The changes of the chemical binding energy of ZrO2 thin films of Zr 3d and O 1s region before and after ion irradiation were investigated by x-ray photoelectron spectroscopy (XPS).

Theoretical Study of the Electronic and Magnetic Properties and Phase Stability of the Full Heusler Compound Pd2CoAl

Based on first principles calculation, a systematical investigation has been performed to study the electronic, magnetic, dynamic, and mechanical properties of the full Heusler compound Pd2CoAl. It is found that the L21-type structure is energetically more stable than the XA-type due to the lower total energy. The obtained lattice constant in cubic ground state is 6.057 Å, which matches well with previous study. The calculated electronic band structure reveals the metallic nature of Pd2CoAl and its total magnetic moment of 1.78 μB is mainly contributed by Co atom from strong spin splitting effect, as indicated with the distinctive distributions of the density of states in two spin directions. Under uniform strains from −5% to +5%, the variation of total magnetic moment has been obtained and it is still caused by the much larger change from Co atom, compared with Pd and Al atoms. The tetragonal structure has further been analyzed and we found that there is possible martensitic phase transformation because the total energy can be further reduced when the cubic structure is varied into the tetragonal one. The large energy difference of 0.165 eV between the tetragonal and cubic phases is found at the c/a ratio of 1.30. The total density of states has been compared between the cubic and tetragonal phases for Pd2CoAl and results show tetragonal phase transformation could reduce the states at the Fermi energy level in both directions. In addition, the dynamic and mechanical stabilities have also been evaluated for Pd2CoAl in both cubic and tetragonal structures and results confirm that the tetragonal phase shows good stability against the cubic phase, which further verifies that the tetragonal phase transformation is highly expected. In the end, the strong elastic anisotropy in the tetragonal structure has been clearly shown with the calculated directional dependence of the Young’s modulus and shear modulus.

Variation of Mechanical Properties of YSZ upon Cubic to Tetragonal Phase Transformation Promoted by Impurity Ni

In fabrication of an SOFC, dissolution of a small amount of NiO into YSZ electrolyte is often observed especially in an anode supported cell. With expectation of changing mechanical properties under similar conditions, measurements were carried out with the samples treated before and after annealing in reducing atmospheres. Elastic moduli were measured by a resonance method, and fracture strength was evaluated by a small punch technique. Some of the sample pieces were annealed with flowing 1%H2-1.2%H2O mixed gas at 900˚C for 15 h, 50 h, and 170 h. Raman scattering spectroscopy revealed that the phase of the annealed samples showed gradual transition from cubic to tetragonal. Young’s modulus and fracture stress of the as-sintered sample showed minimum at a temperature around 400 to 500˚C where large internal friction was observed. This suggests that the mechanical properties were determined not by the concentration of Y2O3 but by the crystal structure that mainly appeared in the sample.

Microwave assisted synthesis and antimicrobial activity of Fe3O4-doped ZrO2 nanoparticles

Composites play important role in dental filling by controlling shrinkage along with correction in teeth's shape and position. Rehabilitation of severely worn dentition can be achieved using mechanically strong composites. This study aims to synthesize zirconia-based composites to be used as dental fillers. Effect of microwave powers (100–900 W) along with Fe3O4 doping are studied on the structural, mechanical and magnetic properties of stabilized zirconia. SEM and TEM reveal formation of spherical nanoparticles with diameter of ∼30 nm. XRD results shows phase pure tetragonal zirconia (t-ZrO2) at microwave power of 500 W without any post heat treatment. Crystallite size calculated from XRD data (∼23 nm) matches well with the previously reported value for stabilization of t-ZrO2. Microwave energy dissipation results in stresses causing volume shrinkage leading to monoclinic to tetragonal phase transformation with higher X-ray density and hardness of ∼1347HV. VSM results show ferromagnetic response with low coercivity (600Oe) value and saturation magnetization (∼2emu/g). It is worth mentioning here that this is one of its kind study reporting synthesis of room temperature stabilized Fe3O4 doped zirconia composites at microwave power of 500 W. Antibacterial studies reveal inhibition zone of ∼32 mm against bacillus bacteria suggesting their potential use as dental filler.

Low energy Ar+ ion irradiation effects in monoclinic zirconia

Argon ion beam induced phase transformation (monoclinic to tetragonal) and bubble formation in monoclinic zirconia (ZrO2) has been studied using grazing incidence X-ray diffraction, electron microscopy, Raman scattering and photoluminescence spectroscopy. Monoclinic zirconia samples were irradiated with low energy (120 keV) Ar+ ions at temperatures 300 K and 143 K. The as-sintered and Ar+ ion irradiated zirconia samples were then irradiated using an excimer laser of wavelength 248 nm (energy 5 eV) to study the defect rich material (after ion irradiation) behavior at extreme condition (where ionization process is dominant). Zirconia was found to undergo a partial phase transformation from monoclinic to tetragonal (≈20%; ion fluence 2 × 1017 ions/cm2) upon Ar+ ion irradiation at 143 K. Further, Ar bubbles were formed and the size of the bubble is found to increase with the ion fluence, irrespective of sample temperature during ion irradiation. The oxygen vacancies (produced during ion irradiation) lead to strain field in the sample and this strain field is the prime cause for phase transformation. The rate of phase transformation was found to be faster in case of ion irradiation at 143 K. Further it was observed that Ar+ ion irradiation lead to creation of defects and laser irradiation on as-sintered zirconia leads to annihilation of defects. However, when laser irradiation was carried out on ion irradiated zirconia, there is a competition between production and annihilation of defects where the production of defects by the Ar+ ion irradiation is a dominant one. Further, the present work confirms the role of O vacancy in the monoclinic to tetragonal phase transformation and the results are consistent with the earlier report (Simeone et al., 2000).

Pulse and Pulse Reverse Electrodeposition of Cubic, Tetragonal and Its Mixed Phase of Ni-W Alloys for Corrosion Applications

Ni-W alloy coatings on mild steel substrate with various crystalline structures were prepared using pulse and pulse reverse electrodeposition method for corrosion protection application. The co-deposition behavior of tungsten and basic electrochemical information of electrolytes were confirmed through cyclic voltammetry studies. The crystalline nature, alloy phase and it is crystal (cubic and tetragonal) phase transformations were confirmed using X-ray diffractions. The corrosion resistance performances of the deposits were studied using Tafel polarization and electrochemical impedance studies. Correlation between the crystal structures and its corrosion resistance performance were explored and tetragonal Ni-W alloy film having better corrosion resistance than cubic Ni-W alloy film. The mixed phase of tetragonal dominated cubic structures in the alloy matrix has the superior corrosion resistance performance. This study confirms the Ni-W alloy films have good corrosion protection and this can be tuned with the modification of crystal structure using various deposition conditions.

Corrosion Behavior and Oxide Films of New Zirconium Cladding Corroded at Different Conditions

Zirconium alloys are mostly served as the cladding materials in water reactors. Corrosion is one of the concerning problems in zirconium utilization. Transition of corrosion occurs every 2~3 μm in thickness, but its mechanism is not confirmed. To study the influence of water chemistry and the mechanism behind transition, a new type of zirconium cladding was tested for three corrosion conditions: the pure water, LiOH solution, LiOH/H3BO3 solution at 360°C/18.6MPa. For all cases, Zr-0.5Sn-0.15Nb-0.5Fe-0.2V cladding had a lower corrosion rate and a longer transition time than N36 cladding. The corrosion results showed that the corrosion rate was the highest and the transition time was the shortest in LiOH solution. Oxide phase information on the oxidized surface was obtained by Raman study. Tetragonal zirconia, embedded in the surface, was found at the beginning of corrosion. As the corrosion time increased, tetragonal phase stress was almost released and the content of tetragonal phase was also decreased to zero at the transition point. Stable tetragonal phase was found on the samples corroded in pure water. However, in LiOH solution, it was eliminated the quickest. The acceleration of transition in LiOH solution is partly resulted from the fast transformation of tetragonal phase. The reason for the longer transition time in N2 cladding can be directly attributed to the smaller decrease of the tetragonal phase.

Nano-BaTiO3 phase transition behavior in coated BaTiO3-based dielectric ceramics

In this work, the phase structure of BaTiO3 nanopowders produced by the alkoxide-hydroxide and the hydrothermal method, respectively, was systemically investigated. BaTiO3 nanopowders with cubic phase produced by the alkoxide-hydroxide method could transform to tetragonal phase when heated to about 1100 °C. Cubic to tetragonal phase transformation behavior of BaTiO3 nanopowders coated with 0.3BZT-0.7BT or 0.03Nb2O5-0.01Co2O3 was studied. The internal stress within core-shell structure was proposed to explain the BaTiO3 phase transformation behaviors. The mismatch of thermal expansion coefficient between core and shell plays a crucial role in cubic to tetragonal phase transformation of BaTiO3. By tuning the composition of shell and the ratio of the shell to the core, the cubic BaTiO3 core can transform to tetragonal phase successfully after sintering at 1100 °C in BaTiO3 based ceramics with core-shell structure and it is mainly resulted by the reduced internal stress between the shell and core.

Effect of ion and neutron irradiation on oxide of PHWR fuel tube material

The effect of heavy ion irradiation on the stability of oxide phase of autoclaved Zircaloy 4 fuel tube material, has been studied using Glancing angle X-ray diffraction (GIXRD) technique after 306 KeV Ar+9 ions irradiation at a dose of 3 × 1019 Ar+9/m2. To estimate the extent of damage, a simulation was carried out using “Stopping and Range of Ions in Matter (SRIM-2008)” computer program based on the Monte Carlo method. For the first time, the oxide formed in 0n1 irradiated fuel tube after 7600 MWD/T burn up in Pressurized Heavy Water Reactor (PHWR) has been characterized using GIXRD technique. The advantage of this technique is that the stress-induced phase transformation, which normally occurs during metallographic sample preparation for optical and electron microscopy, is eliminated. The un-irradiated autoclaved oxide in the steam environment (415 °C and 500 °C), both uniform as well as nodular oxide has been characterized using GIXRD, X-ray photo-electron spectroscopy (XPS), scanning electron microscopy (SEM) attached with Energy Dispersive spectroscopy (EDS). Cross-sectional transmission electron microscopy has been carried out in uniform oxide before and after heavy ion irradiation. It is observed that heavy ion and neutron irradiation induce monoclinic to tetragonal phase transformation in the oxide. Presence of significant fraction of tetragonal ZrO2 phase as well as sub-oxide Zr3O has been identified in the oxide layer near oxide-coolant interface in 0n1 irradiated in-pile sample whereas in unirradiated autoclaved oxide these phases are present in a small fraction near the oxide-metal interface. XPS analysis indicates the difference in the chemical state of alloying element in the oxide when autoclaving is carried out at different temperatures.

Electrical transport properties and complex impedance investigation of Fe3+ and La3+ co-doping (Pb,Sr)TiO3 thin films

This work investigates the impact of Fe3+ and La3+ co-doping on the structural, electrical transport and dielectric relaxation properties of PST thin films. XRD and Raman spectroscopy data show that the Fe3+ and La3+ doping induce a pseudocubic to tetragonal structural phase transformation. Schottky barrier heights calculated from temperature-dependent current–voltage plots for the PST, PSTF and PSLTF films decreased to 1.20, 0.59, and 0.36 eV, respectively. This behavior was directly assigned to the increase in oxygen vacancies. The frequency dependence of sample’s impedance revealed the presence of the typical electrical relaxation phenomenon in all films. Activation energies calculated from the imaginary part of the impedance are 1.73 and 0.57 eV: the high value (1.73 eV, PST films) suggests the presence of long-range oxygen vacancy diffusion, while the lower one (0.57 eV PSLTF films) should be associated to the short-range oxygen vacancy diffusion.

HOT CORROSION OF CERIA-YTTRIA STABILIZED ZIRCONIA PLASMA SPRAYED THERMAL BARRIER COATING BY EUTECTIC VANDIUM PENTAOXIDE-SODIUM SULFATE

The high temperature corrosion behavior of thermal barrier coating (TBC) systemconsisting of IN-738 LC superalloy substrate, air plasma sprayed Ni24.5Cr6Al0.4Y (wt%)bond coat and air plasma sprayed ZrO2-20 wt% ceria-3.6 wt% yttria (CYSZ) ceramic coatwere characterized. The upper surfaces of CYSZ covered with 30 mg/cm2 , mixed 45 wt%Na2SO4-55 wt% V2O5 salt were exposed at different temperatures from 800 to 1000 oC andinteraction times from 1 up to 8 h. The upper surface plan view of the coatings wereidentified for topography, roughness, chemical composition, phases and reaction productsusing scanning electron microscopy, energy dispersive spectroscopy, talysurf, and X-raydiffraction. XRD analyses of the plasma sprayed coatings after hot corrosion confirmed thephase transformation of nontransformable tetragonal (t') into monoclinic phase, presence ofYVO4 and CeVO4 products. Analysis of the hot corrosion CYSZ coating confirmed theformation of high volume fraction of YVO4, with low volume fractions of CeOV4 and CeO2.The formation of these compounds were combined with formation of monoclinic phase (m)from transformation of nontransformable tetragonal phase (t').

Influence of barium borosilicate glass on microstructure and dielectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics

Barium borosilicate (BBS) glass was added as a sintering aid to (Ba0.7Ca0.3)TiO3-Ba(Ti0.8Zr0.2)O3 (BCZT) ceramics at levels from 2 to 15 wt%, yielding enhanced densification. The addition of BBS also induced changes in phase composition, from predominantly tetragonal to orthorhombic at room temperature. It is shown that the changes in phase content are caused by a shift of the orthorhombic to tetragonal phase transformation from below room temperature to ≈50 °C. An additional high temperature transition around 120 °C was also identified. These observations are interpreted in terms of the development of chemical heterogeneity associated with the redistribution of dopant elements (particularly Zr and Ca) through the liquid phase during sintering. The relative permittivity and electric field-induced polarisation values were generally degraded by the presence of the glass phase, but a reduction in ferroelectric hysteresis and improved densification behaviour have potential benefits in dielectric energy storage applications.