Improvement in dielectric,ferroelectric and ferromagnetic characteristics of Ba0.9Sr0.1Zr0.1Ti0.9O3-NiFe2O4 composites

Multiferroic composites with the composition (1-x)Ba_0.9Sr_0.1Zr_0.1Ti_0.9O₃-(x)NiFe₂O₄ (x=0.0, 0.05, 0.10, 0.20 and 0.30) were prepared by mechano-chemical activation technique. Rietveld refined X-ray diffraction pattern shows the formation of individual perovskite (BSZT) and inverse spinel (NFO) phases for all the four composite samples. Microstructural investigation reveals that the inhomogeneity in grains increases with addition of NFO as compared to bare BSZT sample. Dielectric studies show that all the samples exhibit a well-defined ferroelectric to paraelectric transition peak. Further, the diffuseness of the samples increases as NFO content increases. Ferroelectric properties were found to be superior for (1-x)BSZT-(x)NFO sample with x=0.05 and decreases on further increase in NFO content. Dielectric breakdown strength also shows the similar trend as ferroelectricity and shows a maximum for x=0.05 ferrite (NFO) fraction. Magnetic measurement of BSZT-NFO composite samples shows a gradual increase in saturation magnetization and coercive field (H_c) with increasing NFO content.     

Y2O3 doped Ba0.9Ca0.1Ti0.9Sn0.1O3 ceramics with improved piezoelectric properties

Lead-free Ba_0.90Ca_0.10Ti_0.90Sn_0.10O₃-xY₂O₃ (BCTSY, x = 0–0.09) ceramics were prepared by traditional solid-state sintering method. All the BCTSY samples showed pure perovskite structures without detectable impurity. Orthorhombic/tetragonal phase coexisted in the sample of x = 0.03 to 0.07. Remarkable enhancement of the electric properties were achieved at x = 0.03 with d₃₃ of 650 pC/N, K_p of 59.6%, and the remnant polarization P_r of 10.2 μC/cm². The strengthened temperature stability of piezoelectricity is beneficial to the application of the piezoceramics.     

Tuning of electrocaloric performance in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 by induced relaxor-like behavior

Induced relaxor-like behavior is reported by addition of a sintering additive to the (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ solid solution. The effect of Bi₂O₃ sinter additive on microstructure is determined. The phase transition behavior is highlighted by dielectric permittivity measurements. The electrocaloric temperature change is directly measured and comparison with literature data is provided on basis of the material related cooling power. Addition of Bi₂O₃ drastically increases the temperature stability and an ultra-wide temperature range of over 100?K is achieved. The findings path a way to tune electrocaloric materials for optimization of properties for solid-state coolers based on the electrocaloric effect.     

Preparation and electrical conductivity of KTaO3-based proton conductor

KTaO₃ and KTa_0.9M_0.1O_3-α (M = Ti, Hf, Zr) were prepared by solid state reaction at 1330 °C for 2 h and characterized by x-ray diffraction. The AC impedance technique was used to analyze the sintered solid electrolytes in 1%H₂/Ar and dry air atmosphere. Among KTa_0.9M_0.1O_3-α (M = Ti, Hf, Zr), KTa_0.9Zr_0.1O_3-α displays the highest conductivity in 1%H₂/Ar atmosphere. The carriers transport numbers of solid electrolytes were measured by concentration cell method. The results show KTa_0.9Zr_0.1O_3-α is a pure proton conductor below 525 °C. Stability tests show that KTa_0.9Zr_0.1O_3-α has good chemical stability against CO₂ and H₂O.     

Preparation and conductive properties of double perovskite oxides Ba3Ba1+xTa2-xO9-δ

In this work, Ba₃Ba_1+xTa_2-xO_9-δ (x = 0, 0.1, 0.3, and 0.5) double perovskite proton conductors were prepared by solid-state reaction process. Phase compositions and microstructures were characterized by X-ray diffraction and field emission scanning electron microscope techniques. valence and semi-quantitative composition of components were identified by X-ray photoelectron spectroscopy. Conductivities of Ba₃Ba_1+xTa_2-xO_9-δ were then measured under various vapor and oxygen pressures by AC impedance spectroscopy technique. Results revealed linear increase in total conductivities of Ba₃Ba_1+xTa_2-xO_9-δ oxides as a function of temperature. Ba₃Ba_1.3Ta_1.7O_8.55 exhibited the highest total conductivity of 8.41 × 10^?4 S cm^?1 under humidity and 800 °C. The transport numbers calculated by defect equilibria model revealed. Ba₃Ba_1+xTa_2-xO_9-δ oxides as pure proton conductors at 400–800 °C. Also, transport numbers of oxide ions and holes both increased with temperature. Ba₃Ba_1.3Ta_1.7O_8.55 illustrated the highest protonic transport number of 0.60 at 800 °C. In sum, these results suggest that Ba₃Ba_1+xTa_2-xO_9-δ oxides display excellent proton conductivity.     

Band gap narrowing and magnetic properties of transition-metal-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 lead-free ceramics

Transition metal (TM = Mn, Fe, Co, and Ni)-doped Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCZT) lead-free ceramics with excellent optical and magnetic properties are synthesized via a solid-state reaction method. The effects of TM elements on the sintering, structure, optical, and magnetic properties of BCZT ceramics are investigated in detail. Structural phase transition from the coexistence of rhombohedral and tetragonal phases to a single rhombohedral phase is observed owing to grain refinement. A narrow band gap of 1.68 eV is achieved in the Co-doped BCZT. The optical absorption of TM-doped BCZT is enhanced, which is ascribed to the molecular orbital rearrangement caused by lattice distortion. Moreover the magnetic behaviors of TM-doped BCZT are observed. The Fe-doped BCZT presents the most evident ferromagnetism, resulting from the exchange coupling interaction between the Fe³⁺ ions and oxygen vacancies. These results provide additional insight into the use of TM-doped BCZT lead-free ferroelectric ceramics for various applications.     

Low-temperature sintering,structure transition and dielectrical properties of Ba0.85Ca0.15Ti0.9Zr0.1O3 with Na0.5Bi0.5TiO3 addition

Na_0.5Bi_0.5TiO₃-modified Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ ceramics were prepared by solid state route and their structural and dielectric properties were investigated. The sintering temperature of BCTZ ceramics has been significantly decreased from 1460 °C to 1280 °C with NBT addition. All samples showed a pure perovskite structure and a stable solid solution has been formed between BCTZ and NBT. Some tetragonal phase gradually transformed to rhombohedral or cubic phase with the addition of NBT. Dielectric peak gradually becomes broader, revealing that the diffuser behavior was enhanced. The prominent superimposed loss peaks related to thermally activated relaxation process. The values of activation energy of the relaxation process are 1.034, 1.285, 1.308 and 1.353 eV, which could be associated with the migration of oxygen vacancies.     

A novel high-entropy perovskite ceramics Sr0.9La0.1(Zr0.25Sn0.25Ti0.25Hf0.25)O3 with low thermal conductivity and high Seebeck coefficient

In this work, a novel high-entropy n-type thermoelectric material Sr_0.9La_0.1(Zr_0.25Sn_0.25Ti_0.25Hf_0.25)O₃ with pure perovskite phase was prepared using a conventional solid state processing route. The results of TEM and XPS show that various types of crystal defects and lattice distortions, such as oxygen vacancies, edge dislocations, in-phase rotations of octahedron and antiparallel cation displacements coexist in this high-entropy ceramic. At 873 K, the high-entropy ceramics showed both a low thermal conductivity (1.89 W/m/K) and a high Seebeck coefficient (393 μV/K). This work highlights a way to obtain high-performance perovskite-type oxide thermoelectric materials through high-entropy composition design.     

Synthesis and physical property characterisation of phosphonium ionic liquids based on P(O)2(OR)2 and P(O)2(R)2 anions with potential application for corrosion mitigation of magnesium alloys

Phosphonium cation based ionic liquids (ILs) have become of interest due to their unique chemical and electrochemical stability as well as their promising tribological properties. At the same time, interest has also grown in the use of phosphate and phosphinate based ionic liquids for corrosion protection of reactive metals. In this work we describe the synthesis and characterization of six novel ionic liquids based on the tetraalkylphosponium cation coupled with organophosphate and organophosphinate anions and their sulfur analogues. The conductivity and viscosity of these ILs has been measured and discussed in terms of the nature of the interactions, effect of anion basicity and the extent of ionic character. The reaction of the IL with a ZE41 magnesium aerospace alloy surface is also demonstrated.     

Fabrication and properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramics and their multilayer piezoelectric actuators

The lead‐free ceramics with nominal composition (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCTZ) were prepared by a conventional solid‐state reaction combined with a liquid precursor mixing method. Structural, dielectric, piezoelectric, and ferroelectric properties of the ceramics were systematically investigated. Excellent electrical properties of T_c ~ 101°C, tanδ ~ (0.003–0.05), k_p ~ 0.46, d₃₃ ~ 560 pC/N, P_s ~17 μC/cm² and a large strain of 0.43% were reproducibly obtained for the BCTZ ceramics. In addition, BCTZ‐based monolithic multilayer piezoelectric actuators were successfully fabricated by alternately laminating the claimed piezoelectric ceramics and internal‐binder. The actuators show large displacements under low driven voltage. These results highlight that the BCTZ ceramics are excellent candidate for multilayer piezoelectric devices.     

Investigation of ferroelectric,piezoelectric and mechanically coupled properties of lead-free (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 ceramics

Lead-free piezoelectric ceramic (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) has been synthesised by solid-state sintering method and the effect of grain size on ferroelectric, piezoelectric, dielectric, mechanical and piezo-electro-mechanical properties was systematically studied. The compacted powders were sintered at three temperatures i.e. 1450°°C, 1500°C and 1550°C for an optimised duration of 5?h and they have exhibited well resolved morphotropic phase boundary with an average grain size ranging from 10 to 25?µm. Enhanced piezoelectric charge, d₃₃ ～ 560 pC/N and voltage, g₃₃ ～ 14.3?mV?m/N coefficients were obtained for the 1450°C sintered BCZT sample. A maximum strain of around ～0.14% was obtained which is comparable to that of lead-based piezoelectrics. Variation of relative permittivity with temperature revealed that the curves are independent of frequency, indicating the typical relaxor ferroelectric nature of the samples. A systematic study on cyclic loading was performed to evaluate piezo-electro-mechanical coefficients at different loads which showed hysteresis behaviour. High value of elastic modulus (E) and hardness (H) i.e. 262.7?±?38.1?GPa and 13.7?±?1.7?GPa were exhibited by samples sintered at 1450°C, which is higher than that of BCZT synthesised by wet-chemical methods. The results are discussed.     

Thermophysical properties of Yb2O3 doped Gd2Zr2O7 and thermal cycling durability of (Gd0.9Yb0.1)2Zr2O7/YSZ thermal barrier coatings

(Gd_1−xYb_x)₂Zr₂O₇ compounds were synthesized by solid reaction. Yb₂O₃ doped Gd₂Zr₂O₇ exhibited lower thermal conductivities and higher thermal expansion coefficients (TECs) than Gd₂Zr₂O₇. The TECs of (Gd_1−xYb_x)₂Zr₂O₇ ceramics increased with increasing Yb₂O₃ contents. (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) ceramic exhibited the lowest thermal conductivity among all the ceramics studied, within the range of 0.8–1.1 W/mK (20–1600 °C). The Young's modulus of GYbZ bulk is 265.6 ± 11 GPa. GYbZ/YSZ double-ceramic-layer thermal barrier coatings (TBCs) were prepared by electron beam physical vapor deposition (EB-PVD). The coatings had an average life of more than 3700 cycles during flame shock test with a coating surface temperature of ∼1350 °C. Spallation failure of the TBC occurred by delamination cracking within GYbZ layer, which was a result of high temperature gradient in the GYbZ layer and low fracture toughness of GYbZ material.     

Phase structure,mechanical properties and thermal properties of high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B2

A new high-entropy diboride (Hf_0.25Zr_0.25Ta_0.25Sc_0.25)B₂ was designed to investigate the effect of introducing rare-earth metal diboride ScB₂ into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf_0.25Zr_0.25Ta_0.25Sc_0.25)B₂ has high enthalpy driving force, which more easily allows the formation of single-phase AlB₂-type structures between components. The experiments further demonstrate that (Hf_0.25Zr_0.25Ta_0.25Sc_0.25)B₂ possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf_0.25Zr_0.25Ta_0.25Sc_0.25)B₂ showed relatively high hardness (30.7 GPa), elastic modulus (E, G, and B of 522, 231 and 233 GPa, respectively), bending strength (454 MPa), and low thermal conductivity (13.9 W·m^?1·K^?1). The thermal expansion of (Hf_0.25Zr_0.25Ta_0.25Sc_0.25)B₂ is higher than that of ZrB₂ and HfB₂ due to weakened bonding (M d - B p and M dd bonding) and enhanced anharmonic effects. Thus, incorporating Sc into high-entropy diborides can tailor the properties associated with the bonding, which further expands the compositional space of high-entropy diborides.     

Effects of Y2O3 doping on the phase composition,chemical diffusion coefficient and electrochemical properties of CaHfO3 proton conductor

In order to further understand the effect of Y₂O₃ doping on the electrical conductivity of CaHf_1−xY_xO_3−δ, which was prepared by conventional solid-state reaction. The electrical conductivity of CaHf_1−xY_xO_3−δ was measured by two-terminal AC method in an oxygen-rich atmosphere, hydrogen-rich atmosphere and water vapor-rich atmosphere at the temperature between 973 and 1373 K. The test results show that the conductivity of CaHf_1−xY_xO_3−δ first increases and then decreases with x from 0.08 to 0.20, and its total conductivity and conductivity activation energy are 3.88 × 10⁻⁷ to 5.34 × 10⁻⁵S/m and 0.76–0.92eV respectively. Combined with the test results of the H/D isotope effect, it is found that protons are the main conductive carriers in the three different atmosphere at temperatures range of 973–1173 K. In addition, in the temperatures range of 1273–1373 K, the positive holes are the main conductive carriers in the oxygen rich atmosphere, and the vacancies participates in the conductive process as the main conductive carriers in the water vapor rich atmosphere. The chemical diffusion coefficients of CaHf_1−xY_xO_3−δ is 3.9 × 10⁻⁶ to 2.4 × 10⁻⁵ cm²/s in the temperature range of 973–1373 K. According to the test results of electromotive force, the theoretical electromotive force is consistent with the measured electromotive force. The proton transfer number of CaHf_1−xY_xO_3−δ exceeded 97% in hydrogen atmosphere at temperatures from 973 to 1173 K. In sum, these findings of CaHf_1−xY_xO_3−δ can be used as alternative materials for hydrogen sensor electrolytes.     

Critical role of CuO doping on energy storage performance and electromechanical properties of Ba0.8Sr0.1Ca0.1Ti0.9Zr0.1O3 ceramics

CuO doped Ba_0.8Sr_0.1Ca_0.1Ti_0.95Zr_0.05O₃ (BSCTZ) ceramics were prepared by a modified mechano-chemical activation technique with the aim of improving energy storage properties for ceramic capacitor applications. CuO can effectively improve the microstructural characteristics along with a transformation of BSCTZ from classical ferroelectric to relaxor, which is the prime requirement for obtaining high discharge energy density and energy efficiency. The effect of CuO doping on the microstructural, ferroelectric, dielectric, and piezoelectric properties have been systematically studied. The study reveals that an appropriate amount of CuO doping can significantly enhance the morphological properties along with improvement in material density, which is very beneficial in a material for attaining improved energy storage performance. The BSCTZ sample with 3 mol% CuO doping has shown a highly dense microstructure, high saturation polarization (33.01 μC/cm²), low remnant polarization (6.74 μC/cm²), ultrahigh discharge energy density (1.81 J/cm³) and high energy efficiency (81.9%). The CuO doping in BSCTZ has also led to a slight improvement in breakdown strength and electromechanical properties compared to pure BSCTZ ceramics, which is mainly attributed to excellent density and optimum grain size of the material.     

Effect of MnO2 addition on the structure and electric properties of (Ba0.94Ca0.06)(Ti0.9Sn0.1)O3 ceramics

The (Ba_0.94Ca_0.06)(Ti_0.9Sn_0.1)O₃ (BCTS) ceramics with pure perovskite structure were prepared by conventional solid-state reaction route with the addition of 0–0.8?mol% MnO₂. The crystal structure, microstructure, and electric properties were investigated systematically. X-ray diffraction patterns showed that the addition of MnO₂ changed the ratio of the coexistence of orthorhombic and tetragonal phases, which had apparent influences on the piezoelectric properties of ceramics. When the addition amount is 0.2?mol%, the average grain size increases from ~41.88–52.24?µm, and, however, the average grain size decreases with further addition > 0.2?mol%. A good combination of properties and performance could be achieved with the addition of 0.4?mol% MnO₂. The mechanical quality factor Q_m, dielectric loss tanδ, piezoelectric constant d₃₃, and planar electromechanical coefficient k_p measured are 216, 0.011, 578?pC/N, and 0.39, respectively. Therefore, results of this study suggest that the BCTS-Mn ceramics synthesized could exhibit a great potential for piezoelectric component applications.     

Rapid pressure-less and spark plasma sintering of (Ba0.85Ca0.15Zr0.1T0.9)O3 lead-free piezoelectric ceramics

This work shows for the first time the possibility to sinter BCZT powder compacts by rapid heating rates within one hour of sintering, while achieving good piezoelectric properties. The sintering was performed by rapid (heating rates 100 and 200 °C/min) pressure-less sintering (PLS) at 1550 °C/5-60 min and by SPS sintering (100 °C/min, 1450 °C/5?60 min and 1500 °C/15?45 min). The rapid PLS samples reached a relative density up to 94 % and grain sizes of 17–36 μm acquiring d₃₃ up to 414 pC/N. Although the SPS samples reached full density at 1450 °C, their piezoelectric properties worsened due to smaller grains (10?15 μm) as well as formation of cracks at dwell times > 30 min. At elevated SPS temperature of 1500 °C/30 min, the d₃₃ increased to 360 pC/N sustaining full density. Even higher increase in d₃₃ (424 pC/N) of SPS samples was achieved by post-rapid PLS at 1550 °C/60 min resulting from further expansion in grain size.     

Structural,ferroelectric, magnetic and magnetoelectric properties of (1-x) Ba0.85Ca0.15Zr0.1Ti0.9O3 -x La0.67Sr0.33MnO3 lead-free magnetoelectric composites

The influence of an additional La_0.67Sr_0.33MnO₃ (LSMO) magnetic phase on the structural, ferromagnetic, ferroelectric, and magnetoelectric properties of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ferroelectric phase was studied for composites of (1-x)BCZT -xLSMO (x = 0, 25, 50, 75 and 100%). The ferroelectric BCZT sample showed a perovskite single phase formation with a tetragonal crystal structure of the P4mm space group, and the magnetic phase of LSMO presented a rhombohedral crystal structure of R3c space group as shown by XRD. The composite sample with 25% LSMO exhibited large ferroelectric and piezoelectric properties with remnant, saturation polarization, and coercive electric field P_r ~7.74 μC/cm², P_s ~11.69 μC/cm² and E_C ~12.22 kV/cm with a piezoelectric coefficient d₃₃ ~ 231 pC/N. The magnetic characterization for the composites showed that the sample containing 75% of LSMO revealed the highest remnant, saturation magnetization, and coercive field of M_r ~1.358 emu/g, M_s ~19.17 emu/g, and H_C ~33.19 Oe, respectively. Moreover, it revealed the largest magnetoelectric coupling coefficient α_ME ~2.51 mV/cm.Oe with high coupling quality at a lower applied magnetic field. The results highlight the value of these composites as lead-free room temperature magnetoelectric sensors and actuators.     

Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films

High-entropy perovskite thin films, as the prototypical representative of the high-entropy oxides with novel electrical and magnetic features, have recently attracted great attention. Here, we reported the electronic structure and charge transport properties of sol-gel-derived high-entropy Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃ thin films annealed at various temperatures. By means of X-ray photoelectron spectroscopy and absorption spectrum, it is found that the conduction-band-minimum shifts downward and the valence-band-maximum shifts upward with the increase of annealing temperature, leading to the narrowed band gap. Electrical resistance measurements confirmed a semiconductor-like behavior for all the thin films. Two charge transport mechanisms, i.e., the thermally-activated transport mechanism at high temperatures and the activation-less transport mechanism at low temperatures, are identified by a self-consistent analysis method. These findings provide a critical insight into the electronic band structure and charge transport behavior of Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃, validating it as a compelling high-entropy oxide material for future electronic/energy-related technologies.     

Enhancement of the dielectric,piezoelectric, and ferroelectric properties in BiYbO3-modified (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 lead-free ceramics

Lead-free (1−x)(Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃−xBiYbO₃ [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d₃₃~580 pC/N, r~10.9 Ω, k_p~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350 °C. When the measuring electric field is 40 kV/cm, the well-saturated and square-like P–E loops for the ceramics were observed with P_r~12.2 μC/cm² and E_c~1.83 kV/cm.