TiO3 Solid Solution Research Articles

(Sn, Ti)O2 solid solution: Mechanically reinforced SnO2@TiO2@C anode for cycle stability of lithium-ion batteries

Among the various materials investigated for use as anodes in lithium-ion batteries (LIBs), SnO2 faces the significant challenge of substantial volume expansion, severely limiting its practical applications. To address this issue, this paper uses a simple co-precipitation method to synthesize ultrafine SnO2 and TiO2 encapsulated in cross-linked porous carbon (SnO2@TiO2@C), in which SnO2 acts as the primary active material. At the same time, TiO2 functions as a mechanical buffer to mitigate the large volume expansion of SnO2. Additionally, developing (Sn, Ti)O2 solid solution at the interface between TiO2 and SnO2 significantly enhances the bonding between these components, effectively preventing their separation. The cross-linked carbon enhances the conductivity of the SnO2@TiO2@C. The combination of TiO2 and cross-linked carbon produces a synergistic effect that enhances the remarkable cycling performance of SnO2@TiO2@C (769.1 mAh/g after 100 cycles at 0.2 A/g), impressive rate performance (422.3 mAh/g at a discharge rate of 10 A/g) and extended cycle life (403.6 mAh/g after 2000 cycles at 5 A/g). Moreover, this study examined how various ratios of SnO2 and TiO2 influence the electrochemical performance of SnO2@TiO2@C.

Design and electromagnetic shielding of Bi0.5Na0.5TiO3 ceramics as meta-surface absorber for high-frequency microwave application

EMI shielding reduces ambient electromagnetic (EM) radiation by reflecting and absorbing EM waves. Rapid technological growth has increased electronic gadgets and EM radiations, threatening the environment. Microwave materials with high absorption power and cheap cost are crucial for eliminating electromagnetic difficulties in stealth technologies. This study used a conventional solid-state reaction technique to prepare Bi0.5Na0.5TiO3 (BNT) solid solutions and examined their structural, ferroelectric, dielectric, and shielding characteristics. This research describes an EMI shielding material that efficiently absorbs EM wave-induced radiation. Characterizations have been done to evaluate material behavior to support EMI shielding and confirm its absorbing nature. Field emission scanning electron microscopy (FESEM), Raman spectroscopy, and X-ray diffraction (XRD) were employed to examine the surface morphology, local lattice deformation with ionic configuration, and crystal structure. BNT exhibited a rhombohedral structure with R3c symmetry space group with crystallize size 81.5 nm and showed eight Raman active modes with an average grain size of 1.67 μm. The high dielectric constant, reduced dielectric tangent loss, and enhanced polarization value make BNT ceramic a good choice for electrical devices and microwave applications. BNT ceramics showed EMI shielding owing to absorption (SET ∼ −23.65 dB, SEA ∼ −18.91 dB) at 9.2 GHz in the X-band (8.2–12.4 GHz). Meta-surface-based BNT absorbers were designed and simulated in the CST software. The peak depicted the absorption at 9.2 GHz with absorptivity of 91.56 %, 85.03 %, 84.36 %, and 64.6 % for designs 1, 2, 3, and 4, respectively. BNT ceramics have exceptional dielectric absorption properties, and dielectric and magnetic losses, which make them suitable for EMI shielding and absorption applications in the microwave region.

Synthesis of Mesoporous Tetragonal ZrO2, TiO2 and Solid Solutions and Effect of Colloidal Silica on Porosity.

Metal oxides possessing a large surface area, pore volume and desirable pore size provide more varieties and active industrial potentials. Nevertheless, it is very challenging to produce crystal metal oxides while keeping satisfactory porosity features, especially for ternary compositions. High temperature is usually needed to produce crystal metal oxides, which readily leads to the collapse of the pore structure. Herein, by employing a 'soft' dispersant agent and a hard silica template, ZrO2, TiO2 and Zr-Ti solid solutions having a tetragonal crystal structure are produced and the silica-leached materials are characterized from macroscopic to atomistic scales. The micron-sized particulate powders are composed of nanoscale 'building blocks', with crystallite sizes between ~8 and 21 nm. These polycrystalline ceramic powders exhibit a high specific surface area (up to ~200 m2·g-1) and pore volume (up to 0.5 cm3·g-1), with a pore size range of ~5-20 nm. Importantly, the Zr/Ti-O-Si-OH chemical bonds exist on the particle surface, with about two-thirds of the surface covered by silica. The hydroxyl groups can further post-graft organic ligands or directly associate with species. Synthesized mesoporous metal oxides are highly homogenous and could potentially be used in various applications because of their tetragonal structure and porosity features.

Ferromagnetic ordering in Fe: TiO2 solid solutions: A visual electron density mapping by maximum entropy method using powder X-ray data

Magnetic semiconducting FeTiO2 solid solutions with Fe compositions of 6 %, 9 %, and 12 % were analyzed using multi-phase Rietveld refinement analysis for average structure and maximum entropy for electronic structure. VSM analysis showed that the 9 % and 12 % Fe doped TiO2 compositions had a maximum magnetization of 0.3128 emu/g and coercivity of 574 Oe and 568 Oe, respectively. This confirms ferromagnetic tuning with Fe doping at or above 9 %. The MEM electron density at the bond critical points (BCP) of the apical and equatorial (Ti/Fe)–O bonds in 12 % Fe-doped TiO2 is 1.088 e/Å3 and 0.8652 e/Å3, indicating polar covalent bond. This work primarily examines a new empirical correlation between MEM electron density and magnetic parameters. Fe: TiO2 solid solutions have high magnetization and coercivity due to strong and identical (Ti/Fe) – O apical and equatorial polar covalent bonding, with low interstitial charge buildup at non-regular tetrahedral rutile lattice sites.

Influence of sintering temperature on the electrical properties of SrTiO3–BaZrTiO3 ceramics for energy storage applications

The impact of the sintering temperature on the phase composition and electrical properties of 5%SrTiO3–95%BaZr0.15Ti0.85O3 (ST-BZT) ceramics fabricated by solid-state method and consolidated by two-step sintering is presented. A systematic analysis of the phase composition, microstructures, dielectric, ferroelectric, and energy storage characteristics. A di-phase SrTiO3–BaZrTiO3 composite is obtained at low sintering temperatures below 1400 °C. Increasing the sintering temperature causes a shift of the Curie temperature from 62 °C to 55 °C together with changes of permittivity values and of the ferroelectric loops, thus indicating a progressive interdiffusion process at the interfaces, together with a better densification. Remarkably, the ST-BZT composition sintered at 1500 °C exhibits characteristics of a single phase (Ba,Sr) (Zr,Ti)O3 solid solution, with high room temperature permittivity around 2950 and good ferroelectric response (saturation polarization Pmax = 12.6 μC/cm2 and remnant polarization Pr = 2.16 μC/cm2). Consequently, this composition displays a much greater recoverable energy density (Wrec = 54.5 mJ/cm3) in comparison to the ones of the di-phase ST-BZT composites and the parent phases. However, the (Sr0.05Ba0.95) (Zr0.14Ti0.86)O3 solid solution, demonstrates a lower energy efficiency (72%) in comparison to the ST-BZT di-phase composites sintered at lower temperatures, which exhibit higher energy efficiency values around 86%. In addition, the charge-discharge experiments were performed under different electric fields to disclose the difference in energy storage properties in 5%SrTiO3–95%BaZr0.15Ti0.85O3 ceramics. This suggests that the sintering strategy plays a crucial role in determining the energy efficiency of the obtained ceramics. Additionally, all the investigated ST-BZT ceramics present high energy efficiency at low-applied electric fields, suggesting their potential as candidates for energy storage capacitors operating at moderate fields.

Structure and equation of state of Ti-bearing davemaoite: new insights into the chemical heterogeneity in the lower mantle

Abstract Davemaoite (CaSiO3 perovskite) is considered the third most abundant phase in the pyrolytic lower mantle and the second most abundant phase in the subducted mid-ocean ridge basalt (MORB). During the partial melting of the pyrolytic upper mantle, incompatible titanium (Ti) becomes enriched in the basaltic magma, forming Ti-rich MORB. Davemaoite is considered an important Ti-bearing mineral in subducted slabs by forming a Ca(Si,Ti)O3 solid solution. However, the crystal structure and compressibility of Ca(Si,Ti)O3 perovskite solid solution at relevant pressure and temperature conditions were not systematically investigated. In this study, we investigated the structure and equations of state of Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites at room temperature up to 82 GPa and 64 GPa, respectively, by synchrotron X-ray diffraction (XRD). We found that both Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites have a tetragonal structure up to the maximum pressures investigated. Based on the observed data and compared to pure CaSiO3 davemaoite, both Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites are expected to be less dense up to the core-mantle boundary (CMB), and specifically ~1-2 % less dense than CaSiO3 davemaoite in the pressure range of the transition zone (15-25 GPa). Our results suggest that the presence of Ti-bearing davemaoite phases may result in a reduction in the average density of the subducting slabs, which in turn promotes their stagnation in the lower mantle. The presence of low-density Ti-bearing davemaoite phases and subduction of MORB in the lower mantle may also explain the seismic heterogeneity in the lower mantle, such as large low shear velocity provinces (LLSVPs).

Enhanced Photo/Electrocatalytic Hydrogen Evolution by Hydrothermally Derived Cu-Doped TiO2 Solid Solution Nanostructures.

Highly efficient nanocatalysts with a high specific surface area were successfully synthesized by a cost-effective and environmentally friendly hydrothermal method. Structural and elemental purity, size, morphology, specific surface area, and band gap of pristine and 1 to 5% Cu-doped TiO2 nanoparticles were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), energy dispersive X-ray analysis (EDAX), inductively coupled plasma mass spectrometry (ICP-MS), liquid chromatography-high resolution mass spectrometry (LC-HRMS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible diffused reflectance spectroscopy (UV-DRS) studies. The XPS and EPR findings indicated the successful integration of Cu ions into the TiO2 lattice. UV-DRS and BET surface area investigations revealed that with an increase in dopant concentration, Cu-doped TiO2 NPs show a decrease in band gap (3.19-3.08 eV) and an increase in specific surface area (169.9-188.2 m2/g). Among all compositions, 2.5% Cu-doped TiO2 has shown significant H2 evolution with an apparent quantum yield of 17.67%. Furthermore, the electrochemical water-splitting study shows that 5% Cu-doped TiO2 NPs have superiority over pristine TiO2 for H2 evolution reaction. It was thus revealed that the band gap tuning with the desired dopant concentration led to enhanced photo/electrocatalytic sustainable energy applications.

The enhanced energy storage properties of (1-x)(0.94BNT-0.06BT)-x(Bi0.2Na0.2K0.2La0.2Sr0.2)TiO3 solid solutions

A strategy is developed to enhance the energy storage properties of lead-free Bi0.5Na0.5TiO3-based solid solutions, which is implemented through coupling the lattice instability in 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (0.94BNT-0.06BT) ferroelectric with a composition at its morphotropic phase boundary with the chemical disorder in (Bi0.2Na0.2K0.2La0.2Sr0.2)TiO3 (BNKLST) high-entropy ceramic (HEC). The addition of BNKLST in 0.94BNT-0.06BT could suppress the relaxor behaviors in the resulting solid solutions (1-x)(0.94BNT-0.06BT)-xBNKLST. With increasing content x, BNKLST may triggers more polar nano-regions which are in ergodic states at elevated temperatures. As a result, the thermal stability for energy storage properties is increased. In particular, the solid solution with x = 0.3 not only possesses large dielectric constants but also has a low content of oxygen vacancies, beneficial to its dielectric properties; It exhibits an excellent recoverable energy storage density of 2.24 J/cm3 under an electric field of 140 kV/cm, and a good thermal stability at 50 kV/cm with energy storage efficiency η >80 % up to 200 °C. The results demonstrate that the synergy effect of lattice instability and chemical disorder in the solid solutions is effective in enhancing energy storage properties of HECs, facilitating the design and optimization of dielectric energy storage devices.

Structure, dielectric and ferroelectric Properties of (1-x)K0.5Na0.5NbO3 – xBi0.5Na0.5TiO3(0 ≤ x≤ 0.1) Solid Solution

In this study, we prepared lead-free (1-x)K0.5Na0.5NbO3 – xBi0.5Na0.5TiO3 ceramics (KNNBTx) with x = 0, 0.025, 0.05, 0.075, 0.1 using the conventional solid-state reaction method. Scanning electron microscopy analysis revealed dense ceramics with a notable decrease of the average grain size from 3 μm for x = 0–0.3 μm for x ≥ 0.050. X-ray diffraction pattern refinement unveiled that the pure KNN possessed an orthorhombic Amm2 symmetry. In contrast, the KNNBT0.100 composition displayed a tetragonal P4mm symmetry, while the KNNBT0.025 composition exhibited a monoclinic Pm symmetry, suggesting the stabilization of an intermediate phase between the orthorhombic and tetragonal symmetries for x = 0.025. Dielectric measurements indicated that the introduction of small cations in A and B sites of the KNN matrix induced a diffusive phase transition. According to the modified Curie–Weiss law (named also Uchino and Nomura function), the degree of diffuseness (γ) increased from γ = 1.45 to γ 1.74 with increasing x. Raman spectroscopy revealed a frequency upshift of the vibration modes along with broadening of the modes as the NBT composition increased, indicating increased structural disorder in the perovskite structure. Temperature-dependent Raman spectra exhibited the persistence of certain modes at higher temperatures due to the off-centering of cations at A and B sites, a result of the induced substitution-induced disorder in the KNN matrix. Temperature dependent of Raman modes’ frequency have shown substantial modifications at temperatures close to the critical temperatures identified by dielectric measurements. Ferroelectric measurements demonstrated that the incorporation of NBT into the KNN matrix led to significant alterations in the polarization and ferroelectric characteristics of the parent ceramic (pure KNN). As the NBT content increased, the remanent polarization decreased from 13.1 to 3.6 μC/cm2, and the P-E curves became pinched/distorted, indicating a disruption in the long-range order of KNN due to structural and grain size modifications.

High energy storage characteristics for Ba0.9Sr0.1TiO3 (BST) doped Na0.7Bi0.1NbO3 (NBN) ceramics

In recent years, lead-free energy storage ceramics have been widely used as a new type of energy storage material with great application prospects. In this study, a modified NaNbO3 (NN) based ceramic, Na0.7Bi0.1NbO3 (NBN), is used as the matrix, and Ba0.9Sr0.1TiO3 (BST) is added as a doping agent. A series of (1-x)Na0.7Bi0.1NbO3-xBa0.9Sr0.1TiO3 (xBST, x = 0.1, 0.2, 0.3, 0.4) solid solutions have been designed and prepared using the solid-phase sintering method. The breakdown field strength (Eb) of 0.3BST ceramics reached 445 kV/cm, an unexpectedly ultra-high energy storage density (W) of 4.48 J/cm3 and a recoverable energy density (Wrec) of 3.47 J/cm3. In terms of charging and discharging performance, the ceramics have a low charging and discharging time of t0.9 = 1.38 μs. In addition, 0.1BST exhibits a high energy conversion efficiency of η = 87.35 %. These results confirm that (1-x)NBN-xBST ceramics are promising energy storage materials.

Deep insights into the Cu- and W-doped Na0.5Bi0.5TiO3 solid solution: A study focusing on optical, dielectric and electrical properties

Na0.5Bi0.5TiO3 ceramic is among the most promising dielectric materials for several advanced electronic devices due its exceptional features. However, its high oxygen ionic conductivity and wide band-gap energy limit its use for commercial applications. Here, a new Lead-free solid solution 0.995(Na0.5Bi0.5TiO3)-0.005(BiCu0.75W0.25O3), abbreviated 0.995NBT-0.005BCW, was investigated to enhance the electrical and optical performance of NBT ceramic. 0.995NBT-0.005BCW was successfully elaborated by the solid-state technique. The structural, optical, dielectric and electric properties were investigated systematically. The incorporation of BCW into NBT improved the long-range order of the structure, facilitated the poling process, enhanced the electrical properties of the pure NBT and led to the local lattice distortion, generating new electronic levels inside the NBT bandgap. The calculated band gap value ∼3 eV suggests its suitability in power electronic devices. The variation of dielectric constant and dielectric loss with temperature (370–800 K) at different frequencies (100–106 Hz) showed diffused phase transition. The study of dc-conductivity suggests that the substitution of Cu2+ for Ti4+ would formCuTi″, which transforms Cu2+ to Cu+. Our compound is a novel material with interesting properties and offers exciting possibilities for engineering and manufacturing applications.

Effect of Ba2+ ions substitution with Sr2+ ions on the dielectric properties of Ba1− x Sr x TiO3 ceramic solid solution

The temperature dependences of the complex permittivity components ε′ and ε″ for Ba1− x Sr x TiO3 (0.1 ≤ x ≤ 0.7) solid solution obtained by two-stage ceramic technology were investigated. Both components ε′ and ε″ pass through the pronounced maxima near the Curie point. A growth of the ε′ maximum with an increase in the concentration of Sr atoms is associated with a reduction in the average grain size and an increase in the volume fraction of the intergranular layer having a lower ε′ compared to a grain. The increase in the diffusion of the phase transition with the concentration of Sr atoms is due to the greater heterogeneity of the solid solution. Based on the dielectric data, temperature dependences of the local order parameter were plotted.

Room-Temperature Transient Hydrogen Uptake of MgH2 Induced by Nb-Doped TiO2 Solid-Solution Catalysts.

The practical applications of MgH2 as a high-density hydrogen carrier depend heavily on efficient and low-cost catalysts to accelerate the dehydriding/hydriding reactions at moderate temperatures. In the present work, this issue is addressed by synthesizing Nb-doped TiO2 solid-solution-type catalysts that dramatically improve the hydrogen sorption performances of MgH2. The catalyzed MgH2 can absorb 5 wt % of H2 even at room temperature for 20 s, release 6 wt % of H2 at 225 °C within 12 min, and the complete dehydrogenation can be achieved at 150 °C under a dynamic vacuum atmosphere. Density functional theory calculations reveal that Nb doping introduces Nb 4d orbitals with stronger interaction with H 1s into the density of states of TiO2. This considerably enhances both the adsorption and dissociation ability of the H2 molecule on the catalysts surface and the hydrogen diffusion across the specific Mg/Ti(Nb)O2 interface. The successful implementation of solid solution-type catalysts in MgH2 offers a demonstration and inspiration for the development of high-performance catalysts and solid-state hydrogen storage materials.

Effect of Pr3+ Addition on the Electrical Properties of 0.94(Bi0.5Na0.5)TiO3-0.06(Ba0.9Ca0.1)TiO3 Ceramic Obtained by Pechini Method

The influence of Pr3+ addition on the structure and electrical properties of (Bi,Na)TiO3-(Ba,Ca)TiO3 solid solution was investigated. In this work, 0.94(Bi0.5−xNa0.5)TiO3-0.06(Ba0.9Ca0.1)TiO3:xPr3+ (BNBCT6:xPr) with x = 0, 0.1, 0.3, 0.5, and 0.7 mol% ceramics were prepared via a polymeric complex synthesis (Pechini method). Optimal sintering parameters were chosen in order to obtain dense ceramic microstructures. X-ray diffraction confirmed the presence of a perovskite-like structure in all the synthetized powders and sintered samples. As Pr3+ content increased, a large reduction in grain size was observed. BNBCT6:xPr ceramics showed a phase transition from the field-induced ferroelectric to the relaxor phase at ~ 110 °C and a local maximum around 250 °C. Dielectric permittivity was reduced as Pr3+ doping increased. For x = 0.5 mol%, maximum piezoelectric values (d33 = 115 pC/N, − d31 = 27 pC/N, kp = 25%, and kt = 34%) were obtained, while for x = 0.7 mol%, ferroelectric characteristics (Pr = 14 µC/cm2, and Ec = 34.7 kV/cm) were enhanced. Bulk conductivities extracted from the impedance spectra for BNBCT6:xPr were low, consistent with the insulating characteristic of (Bi,Na)TiO3. The achieved electrical properties suggest that BNBCT6:xPr ceramics are a potential candidate for energy transition applications.

Chemical composition of Na0.5Bi0.5TiO3 solid solutions with Sr0.7Bi0.2TiO3 on a local level

Oxygen vacancies in Na0.5Bi0.5TiO3 are of high demand as they stimulate the ionic conductivity essential to solid fuel cell applications. However, their available concentration, which is directly related to introduced A-site vacancies, is very limited. The objective of the present research is to study how the concentration of A-site vacancies may be increased by forming solid solutions with Sr0.7Bi0.2TiO3. A thorough study of heterogeneity and chemical composition of (1-y)Na0.5Bi0.5TiO3-ySr0.7Bi0.2TiO3 ceramics on a local level is conducted and accompanied by impedance measurements. It is shown that the chemical composition of the matrix grains is stable and follows the designed formula, allowing formation of A-site vacancies in a wide concentration range and, in limited amount, also oxygen vacancies. Inclusions, the content and character of which depend on Sr0.7Bi0.2TiO3 concentration, are detected and discussed. Complex impedance studies suggest that the compositions with y < 0.5 preserve low ionic conductivity up to 600–700 °C, but it significantly increases at higher y.

Composition-driven normal ferroelectric to relaxor ferroelectric transition with enhanced electrostriction in ternary NBT-BZ-LT ceramics

The NBT based perovskite ferroelectric oxides with high electrostrictive coefficient (Q 33 ) is gaining attention due to their application in high-precision displacement actuators. Herein, (1 −2x)Na0.5Bi0.5TiO3–xBaZrO3–xLaTiO3 (0.01 ≤ x ≤ 0.07) ceramics are produced through a solid-state reaction. X-ray diffraction is used for the structural analysis of the prepared ceramic materials. The influences of BaZrO3 and LaTiO3 on the piezoelectric and electrostrictive properties in Na0.5Bi0.5TiO3 solid solutions is thoroughly investigated using the dielectric spectra, ferroelectric hysteresis loops, and bipolar strain curves. An electrostrictive coefficient Q 33 of 0.0557 m 4 /C 2 is obtained at x = 0.05, with a moderate S–E hysteresis of 26% at an electric field of 60 kV cm−1. These results indicate that (1 −2x)Na0.5Bi0.5TiO3–xBaZrO3–xLaTiO3 ferroelectric ceramics at x = 0.05 could be a promising material for high-precision displacement actuator applications.

A combined powder x-ray and neutron diffraction studies on (1-x) NaNbO3-x Na0.50Bi0.50TiO3 solid solution

Solid solution of sodium niobate and sodium bismuth titanate [(1-x)NaNbO3-x(Na0.5Bi0.5)TiO3: xNBT)] is an important lead-free eco-friendly piezo-ceramic material. In the present work, we report an investigation of the phase stabilities of this solid solution using powder x-ray and neutron diffraction techniques for the entire range of composition. We observed the disappearance of certain peaks and changes in the main perovskite peaks in the powder diffraction data suggesting structural phase transitions with composition. Rietveld analysis of combined x-ray and neutron powder diffraction data is performed to obtain single correct structural model wherever possible. Detailed analyses of powder diffraction data for composition range 0.0 ≤ x ​< ​0.15 revealed the coexistence of orthorhombic (Pbma) and (Pmc21) phases and an orthorhombic phase with space group Pbnm and cell dimensions √2ap ​× ​√2 bp ​× ​6 cp gets stabilized for 0.15 ≤ x ​< ​0.20. On further increasing NBT content in NaNbO3 matrix (0.20 ≤ x ​< ​0.60), a mixed orthorhombic (Pbnm) phase and tetragonal (P4bm) phase is confirmed by Rietveld refinement. Further, in the composition range 0.60 ≤ x ​≤ ​0.80, the tetragonal (P4bm) phase coexists with the ferroelectric rhombohedral (R3c) phase and finally for composition x ​> ​0.80, it completely transforms to rhombohedral (R3c) phase. The presence of phase coexistence in various composition ranges indicates the first order nature of these phase transitions. A detailed structural phase diagram of the system is presented at ambient conditions.

Enhanced temperature stability of ferroelectric properties in lead-free (1−x)(Bi0.5Na0.4K0.1)TiO3-x(Ba0.5Sr0.5)TiO3 solid solutions

With its complicated composition architecture, (Bi 0.5 Na 0.5 )TiO 3 (BNT)-based relaxor ferroelectrics exhibit distinctive dielectric relaxation phenomena and attractive characteristics. The structural, dielectric, and ferroelectric characteristics of (1– x )(Bi 0.5 Na 0.4 K 0.1 )TiO 3 - x (Ba 0.5 Sr 0.5 )TiO 3 (BNKT- x BST) solid solutions with x = 0–0.4 were thoroughly examined in this study. The x = 0.1 and 0.2 versions exhibited unexpected ferroelectricity enhancement, and the depolarization temperatures and ferroelectric-relaxor transition temperature were both increased compared to that of the BNKT undoped sample. This enhancement is due to the creation of a tetragonal ferroelectric phase after the introduction of a moderate BST member, according to room temperature and temperature-dependent x-ray diffraction data. The characterization of ferroelectric properties indicated that ferroelectricity was enhanced by increasing the rapidly declining temperatures for the remnant polarization and coercive field, compared to those of the BNKT undoped sample. This discovery contributes to a better understanding of the relationship between the structure and properties of complex relaxor ferroelectrics. A phase diagram of the BNKT- x BST solid solution is also provided, which can be used to guide the search for specific lead-free functional materials for the capacitors, actuators, and transducers based on this eco-friendly system.

Self-stabilization of the equilibrium state in ferroelectric thin films

(K,Na)NbO3 is a lead-free and sustainable ferroelectric material with electromechanical parameters comparable to Pb(Zr,Ti)O3 (PZT) and other lead-based solid solutions. It is therefore a promising candidate for caloric cooling and energy harvesting applications. Specifically, the structural transition from the low-temperature Mc- to the high-temperature c-phase displays a rich hierarchical order of domains and superdomains, that forms at specific strain conditions. The relevant length scales are few tens of nanometers for the domain and few micrometers for the superdomain size, respectively. Phase-field calculations show that this hierarchical order adds to the total free energy of the solid. Thus, domains and their formation has a strong impact on the functional properties relevant for electrocaloric cooling or energy harvesting applications. However, monitoring the formation of domains and superdomains is difficult and requires both, high spatial and high temporal resolution of the experiment. Synchrotron-based time-resolved X-ray diffraction methods in combination with scanning imaging X-ray microscopy is applied to resolve the local dynamics of the domain morphology with sub-micrometer spatial and nanosecond temporal resolution. In this regime, the material displays a novel self-stabilization mechanism of the domain morphology, which may be a general property of first-order phase transitions.

Optimizing strain response in lead-free (Bi0.5Na0.5)TiO3-BaTiO3-NaNbO3 solid solutions via ferroelectric / (non-)ergodic relaxor phase boundary engineering

Lead-free bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized. In this work, a large strain response of 0.61% is achieved in lead-free (0.94-x%)(Bi0.5Na0.5)TiO3-0.06BaTiO3-x%NaNbO3 (x = 0 –6, BNT-6BT-xNN) ceramics with the composition of x = 3.5 in a pseudo-cubic structure. Coexistence of ferroelectric (FE) and relaxor (RE) domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor (ER) and non-ergodic (NR) states thanks to the substitution of antiferroelectric NN. BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature (RT) and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state. This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.