CaZrO3 Research Articles

Enhanced dielectric reliability in the X9R‐type Bi1/2Na1/2TiO3‐CaZrO3 relaxor ferroelectric ceramics

AbstractHigh‐performance dielectric ceramic capacitors for automotive applications require high operation temperature, thermal stability, and reliability for dielectric ceramics. A broad composition search has been carried out to replace the existing BaTiO3‐based dielectrics having limited upper operating temperature due to the relatively low Curie temperature at around 120°C. However, most of the developed compositions are too complicated and compositionally sensitive, making them difficult to commercialize. This study introduces a dielectrically reliable ceramic system based on Bi1/2Na1/2TiO3 (BNT) with a wide operation temperature range simply by adding paraelectric CaZrO3 (CZ). At 15 mol% addition of CZ to BNT, the permittivity variation within ±15% from −55 to 280°C was achieved, which surpasses the EIA‐X9R standard. Moreover, the dielectric reliability was shown with low dielectric loss (tanδ < 0.02) for the aforementioned temperature range and remarkable dielectric breakdown strength (∼260 kV/cm) at room temperature. Along with the proposal of a promising high‐performance dielectric material, structural analysis and dielectric behavior investigation as a function of CZ contents were presented.

Effects of O2/Ar Ratio on Preparation and Dielectric Properties of CaZrO3 Films by Radio Frequency (RF) Magnetron Sputtering.

CaZrO3 (CZO) thin films were deposited on Pt/Ti/SiO2/Si substrates at 450 °C by radio-frequency magnetron sputtering technology. The microstructures and dielectric properties of CZO thin films were investigated. X-ray diffraction analysis reveals that the perovskite orthogonal CZO phase would be promoted by a higher O2 partial pressure in the flow ratio of O2/Ar after thin films were annealed at 700 °C for 3 h in air. The films prepared under the flow ratio of O2/Ar (20:40, 30:40 and 40:40) show the main perovskite crystal phase of CaZrO3 with a small amount of Ca0.2Zr0.8O1.8. The main crystal phase was Ca0.2Zr0.8O1.8 when the film was deposited under an O2/Ar ratio of 40:10. The annealed film with a 40:40 O2/Ar ratio exhibits a dielectric performance with a high dielectric constant (εr) of 25 at 1 MHz, a temperature coefficient of permittivity of not more than 122.7 ppm/°C from 0 °C to 125 °C, and a low leakage current density of about 2 × 10-7 A/cm2 at 30 V with an ohmic conduction mechanism.

Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO3, CaTiO3, PbTiO3, SrTiO3, BaZrO3, CaZrO3, PbZrO3 and SrZrO3 Perovskites.

We performed B3PW and B3LYP computations for BaTiO3 (BTO), CaTiO3 (CTO), PbTiO3 (PTO), SrTiO3 (STO), BaZrO3 (BZO), CaZrO3 (CZO), PbZrO3 (PZO) and SrZrO3 (SZO) perovskite neutral (001) along with polar (011) as well as (111) surfaces. For the neutral AO- as well as BO2-terminated (001) surfaces, in most cases, all upper-layer atoms relax inwards, although the second-layer atoms shift outwards. On the (001) BO2-terminated surface, the second-layer metal atoms, as a rule, exhibit larger atomic relaxations than the second-layer O atoms. For most ABO3 perovskites, the (001) surface rumpling s is bigger for the AO- than BO2-terminated surfaces. In contrast, the surface energies, for both (001) terminations, are practically identical. Conversely, different (011) surface terminations exhibit quite different surface energies for the O-terminated, A-terminated and BO-terminated surfaces. Our computed ABO3 perovskite (111) surface energies are always significantly larger than the neutral (001) as well as polar (011) surface energies. Our computed ABO3 perovskite bulk B-O chemical bond covalency increases near their neutral (001) and especially polar (011) surfaces.

Phase relationships at 1673 K and thermodynamic evaluation of ZrO2–SrO–CaO system

Twelve samples of the ZrO2–SrO–CaO system were prepared, quenched from 1673 K to room temperature, and characterized by XRD and SEM/EDS methods to investigate the phase relations of the ZrO2–SrO–CaO system at 1673 K. The results showed that four solid solution phases exist: (Sr, Ca)ZrO3, (Sr, Ca)2ZrO4, (Sr, Ca)3Zr2O7 and (Sr, Ca)4Zr3O10. Based on the experiments as well as the literature data, the ZrO2–SrO–CaO system was evaluated by the CALPHAD (CALculation of PHAse Diagram) method, and the isothermal sections at 1673 K and 2073 K and a liquidus projection were calculated. The calculation results were in good agreement with most of experimental results, which proves that the database is self-consistent and reliable, and this work can be applied to the design of novel refractories.

Enhanced DC-biased energy-storage performance in lead-free relaxor ferroelectric ceramics for high-density power converters

Dielectric energy-storage capacitors are among the main enabling technologies in high-density power converters, in which lead-free relaxor ferroelectric ceramics have been paid particular attention to. However, low energy-storage performance at elevated temperature and high electric field, and the lack of application-oriented evaluation are among the primary blocks stumbling their progress. As a demonstration, 0.87BaTiO3-0.13Bi[Zn2/3(Nb0.85Ta0.15)1/3]O3 (BTBZNT) lead-free relaxor ferroelectric ceramics were modified by linear dielectric CaZrO3 (CZ) with various contents of 0, 0.1, 0.2, and 0.3 (CZ0, CZ1, CZ2, and CZ3). XRD and Raman results reveal major perovskite phases, and densely sintered ceramics were witnessed from the SEM images. Unchanged weakly coupled relaxor behavior was confirmed by the big critical coefficient of 1.6–1.8 from the modified Curie–Weiss law and the large activation energy of 0.29–0.32 eV from the Volgel–Fulcher fittings, and CZ was found to suppress high-temperature loss. From the normal polarization–electric field (P–E) loops, CZ0 is optimal for energy-storage owing to the highest discharged energy density and modest efficiency. Nevertheless, from the application-oriented DC-biased P–E loops, CZ1 is oppositely superior to CZ0 because of the higher permittivity and lower loss leading to higher discharged energy density and efficiency at DC-biased electric field. Moreover, CZ1 outperforms CZ0 in the higher capacitance density and lower temperature rise at higher temperature and electric field. Enhanced DC-biased energy-storage performance in BTBZNT ceramics modified by CZ was achieved, which should enlighten the advance of energy-storage ceramics targeting the application in high-density power converters.

Hierarchically polar structures induced superb energy storage properties for relaxor Bi0.5Na0.5TiO3-based ceramics

Electrostatic capacitors are fundamental components in electronics and electric power systems because of their inherent superiorities of charging/discharging speed and power density. However, energy storage properties (ESPs) of the top promising relaxor ferroelectric (RFE) are intimately entwined symmetry of local lattice and dynamics of nano-scaled polar structure. Herein, hierarchically polar structure and oxygen octahedral tilting can be induced in the 0.7Bi0.5Na0.5TiO3-0.3Na0.91Bi0.09Nb0.94Mg0.06O3 (BNT-NBNM) matrix with the addition of CaZrO3 (CZ) to achieve outstanding comprehensive ESPs. The chemically induced coexisting triple phases of tetragonal P4bm, orthorhombic P21ma and Pnma2 bring forth hierarchically polar structure, featuring nanodomains and slush-like polar clusters embedded in stripe submicro-domains, as indicated by morphological observations, splitting of diffraction spots and polar state distributions. Accordingly, an ultrahigh recoverable energy storage density Wrec = 7.5 J cm−3 concurrent with a high-efficiency η = 94.5 % at a breakdown electric field of 510 kV cm−1 can be attained in BNT-NBNM-0.05CZ RFE ceramic. In addition, the optimal composition also displays excellent stability (Wrec = 5.1 ± 0.1 J cm−3, η = 92.7% ± 1%, 20–170 °C and Wrec = 5.2 ± 0.2 J cm−3, η = 92.1% ± 1.3%, 5–500 Hz) at 410 kV cm−1. The present work provides a new perspective for designing lead-free RFE ceramics with ultra-high ESPs that benefit from hierarchically polar structures.

Complete set of ferro/piezoelectric properties of BaZrO3 and (Ba,Ca)ZrO3 doped KNLNS-based electroceramics

Full piezoelectric characterization of lead-free 0.96(K0.48Na0.52)0.95Li0.05Nb0.93Sb0.07O3-0.04BaZrO3 (KNLNS0.07-BZ) and 0.96(K0.48Na0.52)0.95Li0.05Nb0.94Sb0.06O3-0.04Ba0.94Ca0.06ZrO3 (KNLNS0.06-BCZ) ceramics was carried out by complex impedance spectroscopy using different resonance modes. These piezoelectric ceramics were synthesized by conventional solid-state method. The microstructural results showed that the crystals present a cubic-like morphology. Structural and dielectric characterization demonstrated the existence of an orthorhombic-tetragonal (O-T) and a rhombohedral-tetragonal (R-T) polymorphic phase transitions in KNLNS0.06-BCZ and KNLNS0.07-BZ, respectively. The ferroelectric and thermal stability measurements evidenced that the O-T phase transition is stable at higher temperatures compared with the sample with R-T coexistence. Both compositions have high piezoelectric properties and some principal parameters obtained are: d33 = 408 pC/N, 347 pC/N; d31 = −141 pC/N, −113 pC/N; d15 = 304 pC/N, 224 pC/N; kp = 48%; kt = 38%, 47%; k15 = 44%, 46%; and Tc = 185 °C, 233 °C, for KNLNS0.07-BZ and KNLNS0.06-BCZ, respectively.

Exploring the high-performance (1-x)BaTiO3-xCaZrO3 piezoceramics with multiphase coexistence (R-O-T) from internal lattice distortion and domain features

Although the multiphase coexistence has made great achievements in improving the piezoelectric properties of barium titanate-based (BT) ceramics, the problems such as internal lattice distortion and external physical mechanism at the phase boundary still remain. Here, we have studied the phase structure, atomic parameters and domain structure of (1-x)BaTiO3-xCaZrO3 (abbreviated as BT-xCZ) ceramics. By regulating the phase transition temperatures, the rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence (x = 0.06) is realized at room temperature. Notably, high piezoelectric constant of d33 ∼ 445 ± 20 pC/N and large electromechanical coupling factor of kp = 55% are obtained at x = 0.06. With the doping of CaZrO3 (CZ), the lattice of ceramics is distorted, thereby increasing the ferroelectricity and piezoelectricity. Importantly, the domain structure of BT-xCZ ceramics observed by the acid etching technology further proves that the high piezoelectricity is attributed to the multiphase coexistence and reduction of the domain wall energy density.

Color tuning in CaZrO3:RE3+ perovskite by choice of rare earth ion

Color tunable phosphor has been attracting the scientific community owing to its multifunctional application in optoelectronics, solid-state lighting and bioimaging. Achieving the same in a single host will be quite interesting from a designer’s perspective in narrowing down the cost and scaling it. In the current work, we have explored gel-combustion synthesized rare earth (RE) doped CaZrO3 (CZO) perovskite as a phosphor for covering a wide range of tunable colors ranging from ultraviolet (UV) → Visible. We have doped different rare earth ions such as Sm3+, Eu3+, Gd3+, and Tb3+ in CZO and explored their optical properties, local structure, excited-state lifetime, etc. Doping of RE ions in CZO leads to efficient luminescence facilitated by host→dopant energy transfer. CaZrO3:Sm3+(CZOS) displayed reddish-orange emission with two different lifetime values viz. 20 and 72 μs and are attributed respectively to Sm3+ ion located at Zr4+ (24%) and Ca2+ (76%) sites, respectively. CaZrO3:Eu3+(CZOE) on the other hand, displayed bright, highly pure, and narrow red emission with incredibly low non-radiative transition probability (ANR), high red branching ratio (β2) with internal quantum yield (IQY) of 71.4%. Based on the Stark splitting investigation; europium symmetry in CZOE was found to be quite low with the C6 point group. The lifetime of CZOE though suggested biexponential decay, but Eu3+ ions are localized only at Ca2+ ion; one closer to charge compensating calcium vacancies (194 μs) and other (425 μs) at far off distance from the same. CaZrO3:Gd3+(CZOG) emits highly energetic UV radiation, which can be quite useful in photothermal therapy. Lastly CaZrO3:Tb3+(CZOT) phosphor emits bright green light, but it is displaying a single exponential decay profile stabilizing only on symmetric Zr4+ sites as suggested by the intense magnetic dipole transition (MDT). We believe such a complete spectrum of work in designing a tunable phosphor would be quite beneficial in phosphor converted light emitting diodes (pc-LEDs) employing red-green-blue (RGB) strategy.

Nanocrystalline Heterogeneous Multiferroics Based on Yttrium Ferrite (Core) with Calcium Zirconate (Titanate) Shell

Nanocrystalline YFeO3–CaZr(Ti)O3 powders were synthesized by the sequential deposition method. The structure of the YFeO3–CaZr(Ti)O3 nanocrystals fits into the core–shell spherical particle model. The nanocrystalline YFeO3–CaZr(Ti)O3 powders synthesized contain yttrium orthoferrite and calcium zirconate (titanate) single phases. Materials based on YFeO3–CaZr(Ti)O3 are magnetically soft.

Piezoelectric, electrical and energy harvesting properties of (Na0.52K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3 ceramics

In this study, (Na,K,Li)(Nb,Sb,Ta)O3 ceramics substituted with (Sr,Ca)ZrO3 by conventional solid state method were manufactured and their dielectric and piezoelectric properties were investigated. The (Na,K,Li)(Nb,Sb,Ta)O3 ceramics substituted with 0.01 (Sr,Ca)ZrO3 showed excellent piezoelectric properties. The density(ρ), piezoelectric constant(d33), and the piezoelectric voltage constant (g33), planar piezoelectric coupling coefficient(kp), mechanical quality factor(Qm), and dielectric constant(εr) showed the excellent values of 4.55 g/cm3, 254pC/N, 26.17(×10−3 Vm/N) 0.46, 156, and 1096, respectively. The multilayer piezoelectric energy harvester was fabricated using the above composition ceramics by tape casting methods. When driving frequency was 80 Hz under gravity acceleration 1G, the multilayer energy harvester with the size of 30 mm ×3 mm ×1 mm showed the maximum output voltage of 1.1V at no load. And the maximum output power 3.28 µW of the harvester was also shown at the 50 Hz under gravity acceleration 1G.

Precise prediction of dielectric property for CaZrO3 ceramic

As for CaZrO3 (CZ) ceramic, the reported dielectric property values, especially dielectric constants, were much different from 23 to 32, which is reliable and credible? Without precise property data, CZ can’t be further developed and utilized accurately. Herein, CZ ceramic was fabricated by a traditional two-step sintering process, then simulated and calculated the dielectric properties precisely at a microscopic polarization angle using the lattice vibrational spectra and the Clausius–Mossotti (C–M) as well as damping equations. The Raman and Fourier transform far-infrared modes were analyzed and used to predict the intrinsic properties, which were consistent well with the values calculated from C–M and damping equations. The intrinsic permittivity, after precise prediction, is about 20, which is reliable and credible. As for the dielectric loss, the value of about [Formula: see text] was obtained after precise calculation, which is similar to other results.

Electrospun fabrication, excellent high-temperature thermal insulation and alkali resistance performance of calcium zirconate fiber

CaZrO3 (CZO) precursor fibers were prepared by sol-gel method and electrospinning technique from solutions which contained aqueous precursors of calcium and zirconium ions and polyethylene oxide. The crystallization of CZO fibers was a concurrent process with the decomposition of organics. The evolution process was characterized by Fourier transform infrared (FT-IR) and Raman spectra, thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The heat-conducting property and high temperature stability of fibers were characterized by the measurements of thermal conductivity and heating permanent linear change, respectively. The fibers were treated in NaOH solution at 80 °C to characterize the alkali resistance. The results showed that CZO fibers had the lower thermal conductivity than the other reported forms of CZO materials, and they possessed excellent stability up to 1100 °C with thermal shrinkage less than 1.2% and excellent corrosion resistance to alkalis. Hence, CZO fiber could be used as a suitable corrosion resistant refractory material for high-temperature thermal insulation.

Mechanism of photoluminescence in intrinsically disordered CaZrO3 crystals: First principles modeling of the excited electronic states

CaZrO3 (CZO) powders obtained by the polymeric precursor method at 400 °C, and then, the samples were annealed at different temperatures (400, 600, 800, and 1000 °C) and characterized by X-ray diffraction, Raman and ultraviolet–visible spectroscopic methods, along with photoluminescence (PL) emissions. First principle calculations based on the density functional theory (DFT), using a periodic cell models, provide a theoretical framework for understanding the PL spectra based on the localization and characterization of the ground and electronic excited states. Fundamental (singlet, s) and excited (singlet, s*, and triplet, t*) electronic states were localized and characterized using the ideal and distorted structures of CZO. Their corresponding geometries, electronic structures, and vibrational frequencies were obtained. A relationship between the different morphologies and structural behavior has also been established.Polarized structures were identified by the redistribution of the 4dz2, 4dyz, and 4dxy (Zr) orbitals at the conduction band and the 2pz (O) orbital in the valence band for s, s* and t*. Analysis of the vibrational eigenvector modes of these electronic states reveals a relationship between them via asymmetric bending and stretching modes that arise from Zr atom displacements due to polyhedral [ZrO6] distortion. Furthermore, the results provided an insight into the PL emissions of the as-synthesized CaZrO3 and led to the conclusion that the presence of electronically excited states is strongly related to the structural order-disorder effects (polyhedral distortion) at short range for both [ZrO6] and [CaO8] clusters.

Enhanced piezoelectric property and microstructure of large CaZrO3-doped Na0.5K0.5NbO3-based single crystal with 20 mm over

CaZrO3(CZ)-doped Na0.5K0.5NbO3(NKN)-based single crystals with 20mm over were prepared by a seed-free solid-state crystal growth (SFSSCG) method. The microstructure, piezoelectric and dielectric properties of the crystal were investigated. The results show that the piezoelectric constant d33 of this crystal is evidently enhanced up to 488pC/N with the addition of CZ. Two dielectric anomalies appear at 391 and 149°C, corresponding to the tetragonal→cubic and orthorhombic→tetragonal phase transition, respectively. There exists two domains (90° and 180°) in the crystal. These results show that this NKN-based crystal is a promising lead-free piezoelectric material for applications.

Modification of microstructure and electrical properties in (K,Na)NbO3-(Ba,Ca)ZrO3 ceramics by changing K/Na ratio

ABSTRACT0.94(KxNa1-x)NbO3-0.06Ba0.8Ca0.2ZrO3 lead-free ceramics were prepared by the conventional solid-state method, and the effects of K/Na ratio on their piezoelectric properties were investigated in detail. Their grain sizes gradually decrease as the K/Na contents reach 60/40. By optimizing the K/Na ratio, an optimum piezoelectric behavior of d33∼270 pC/N and kp∼45% can be observed in the ceramics with x = 0.48. In addition, its piezoelectric activity was also strongly sensitive to the sintering temperatures and poling conditions, that is, d33 increases from 120 pC/N to 270 pC/N by a sintering temperature of 1160 °C and an optimum poling condition of >120 °C and 3 kV/mm. As a result, the modification of K/Na ratio is an effective way to further improve piezoelectric properties of KNN ceramics.

Phase Structure, Microstructure and Electrical Properties of BCZT Ceramics Prepared by Seed-Induced Method

The effect of particle sizes of CaZrO3 (CZ) nanocrystal on the phase structure, microstructure and electrical properties of Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) was studied. The CaCO3 and ZrO2 were used as starting materials for CaZrO3 (CZ) seeds synthesized by the molten-salt method. The results were found that the CZ powder has a pure perovskite with the particle size about 370 to 460 nm. Then the CZ nanocrystals were mixed with the metal oxides BaCO3, CaCO3, ZrO2 and TiO2 by mixed oxide method. The phase structure, microstructure and electrical properties of BCZT ceramic were investigated as a function of particle size and concentration of CZ. The results indicated that all samples showed pure perovskite phase. The highest values of density, grain size, dielectric constant (εr) and piezoelectric coefficient (d33) were 5.50 g/cm3, 10.95 μm, 2992 and 446 pC/N, respectively which obtained at the CZ seed size 459 nm.

Enhanced energy-storage performance and dielectric characterization of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 modified by CaZrO3

The 0.94Bi0.5Na0.5TiO3–0.06BaTiO3(BNBT6) introduced by CaZrO3(CZ) lead-free ferroelectric ceramics are successfully fabricated by conventional solid state reaction. The influence of CZ substitution on the phase transition, microstructure, dielectric, ferroelectric, and energy storage properties of (1 − x)BNBT6-xCZ ceramics are systematically investigated. The energy-storage density 0.7 J/cm3 under the electric field 70 kV/cm is obtained in the 0.97BNBT6-0.03CZ. In addition, its energy-storage property exhibits thermal stability at the temperature range of 30–130 °C.

A theoretical investigation of the structural and electronic properties of orthorhombic CaZrO3

A CaZrO3 (CZO) powder was prepared by the soft chemical, polymeric precursor method (PPM). The CZO crystalline structure was investigated by powder X-ray diffraction (XDR), Retvield Refinament data, Raman spectra and ultraviolet–visible absorption spectroscopy. A theoretical study was performed using a periodic quantum mechanical calculation (CRYSTAL09 program). The periodic model built for the crystalline CZO structure was consistent with the experimental data obtained from structural and electronic properties. These results show that the material has an orthorhombic structure with experimental and theoretical gap values of 5.7eV and 6.2eV, respectively. In this article, we discuss the hybridization process of the oxygen p-orbitals and of the zirconium d-orbitals and analyze their band structures and density of states (partial and total).

Impedance Spectroscopy of (Bi1/2Na1/2)TiO3–BaTiO3 Based High‐Temperature Dielectrics

The dielectric properties of CaZrO3 (CZ) modified 0.94Bi1/2Na1/2TiO3 (BNT)–0.06BaTiO3 (BT) and 0.82(0.94BNT–0.06BT)–0.18(K1/2Na1/2)NbO3 have been investigated by impedance spectroscopy over a wide temperature range. The presence of a highly polarizable phase in addition to a bulk response is revealed by electric modulus (M″) spectra in both systems. The relaxation frequency of the polar phase follows the Vogel–Fulcher law below the Burns temperature which decreases with increasing CZ content. The dc conductivity of the ceramics is dominated by the bulk response which follows the Arrhenius law with an activation energy ranging from 1.4 to 1.7 eV and has an oxygen partial pressure dependence consistent with n‐type semiconductivity. This information is pertinent to on‐going compositional development of relaxor‐based high‐temperature dielectrics.