Pseudocubic Perovskite Research Articles

Fine-grained BCZT piezoelectric ceramics by combining high-energy mechanochemical synthesis and hot-press sintering

Different stoichiometries of lead-free BaZr0.2Ti0.8O3–Ba0.7Ca0.3TiO3 (BCZT) prepared by mechanosynthesis and sintered by either conventional sintering (CS) or hot pressing (HP) techniques were studied to establish the dependence of piezoelectric and dielectric properties on sintering parameters and microstructure. All synthesized stoichiometries showed a pseudocubic perovskite phase with homogeneously distributed A- and B-cations in the structure. The BCZT retained the pseudocubic symmetry after sintering and an average grain size <1.8 µm was obtained in all cases. HP sintering hindered the secondary phase segregation observed in the CS ceramics and increased the relative density. Piezoelectric coefficients (d33) ranging from 5.1 to 21 pC/N and from 10.0 to 88.0 pC/N were obtained for CS and HP ceramics, respectively, despite the pseudocubic symmetry and the fine grain size. The higher d33 values for the HP ceramics are a consequence of the higher density, better chemical homogeneity and lower sintering temperature and time required for the mechanosynthesized BCZT powders with high sintering activity.

Structural, Mechanical, and Optoelectronic Properties of CH3NH3PbI3 as a Photoactive Layer in Perovskite Solar Cell

The structural, electronic, mechanical, and optical properties of pseudo-cubic CH3NH3PbI3 perovskite have been studied within the framework of density functional theory, in line with solar cell applications. The computed values of lattice and elastic constants concurred with the available theoretical and experimental data. This compound has a semi-conducting behavior, with a direct band gap of about 1.49 eV. Note that the solar radiation spectrum has a maximum energy intensity value of approximately 1.50 eV. Thus, semiconductors with such gaps are preferred for photovoltaic applications. Its elastic parameters reveal that it is a ductile material that is mechanically stable. Optical descriptors such as refractive index, reflectivity, extinction, energy loss, and absorption have been explored with the aim of establishing the optical features of the material. Our findings demonstrate that this perovskite is suitable for solar cell applications based on the size and nature of the band gap, as also supported by the obtained upper limit value of simulated power conversion efficiency via the spectroscopic limited maximum efficiency mathematical model.

Magnetic, Antiferroelectric-like Behavior and Resistance Switching Properties in BiFeO3-CaMnO3 Polycrystalline Thin Films

The effect of ferromagnetic CaMnO3 (CMO) addition to structural, magnetic, dielectric, and ferroelectric properties of BiFeO3 is presented. X-ray diffraction and Raman investigation allowed the identification of a single pseudocubic perovskite structure. The magnetic measurement showed that the prepared films exhibit a ferromagnetic behavior at a low temperature with both coercive field and remnant magnetization increased with increasing CMO content. However, a deterioration of magnetization was observed at room temperature. Ferroelectric study revealed an antiferroelectric-like behavior with a pinched P–E hysteresis loop for 5% CMO doping BFO, resulting in low remnant polarization and double hysteresis loops. Whereas, high remnant polarization and coercive field with a likely square hysteresis loop are obtained for 10% CMO addition. Furthermore, a bipolar resistive switching behavior with a threshold voltage of about 1.8 V is observed for high doped film that can be linked to the ferroelectric polarization switching.

Ordered deficient perovskite La2/3TiO3 films grown via molecular beam epitaxy

As the parent compound of a promising solid electrolyte material Li3xLa2/3−xTiO3, the perovskite La2/3TiO3 has potential for advancing research on Li-intercalated ionic conductors. Epitaxial La2/3TiO3 films have been grown by molecular beam epitaxy using a growth process consisting of deposition and annealing cycles, with in situ monitoring by electron diffraction. X-ray absorption spectroscopy confirms the tetravalent state of Ti in La2/3TiO3, and the as-grown films are insulating. X-ray diffraction reveals the presence of half-order peaks, indicating a doubling of the pseudocubic perovskite unit cell due to the ordering of La vacancies in alternating A-site layers. These results demonstrate that single-phase, vacancy-ordered epitaxial films of La2/3TiO3 can be stabilized with excellent crystalline and electronic properties over wafer-sized areas, making possible Li-ion intercalation studies in films with well-defined domain boundary properties. Such boundaries are known to profoundly influence Li-ion conduction within the material. Understanding the effects of domain boundaries on Li-ion conduction could lead to improvements in solid-state battery technology and pave the way for the development of more efficient and safer energy storage devices.

Perovskite lattice constant prediction framework using optimized artificial neural network and fuzzy logic models by metaheuristic algorithms

Perovskites have gained significant attention in recent years due to their unique and versatile material properties. The lattice parameters of the perovskite compounds play a crucial role in the engineering of layers and substrates for heteroepitaxial thin films. As an essential parameter in the cubic perovskite structure, the lattice constant, plays a significant role in the development of materials for specific technological applications and serves as a distinctive identifier of the crystal structure of the material. In the field of materials science, advanced Computational Intelligence (CI)-based techniques have become increasingly important for simulating the relationship between the physicochemical parameters of chemical elements and the physical properties of materials and compounds. Hence, this paper presents efficient techniques based on artificial neural network (ANN) and fuzzy logic to predict the lattice constants of pseudo-cubic and cubic perovskites. The identification of optimized parameters for the ANN and fuzzy logic models is accomplished using innovative metaheuristic algorithms such as, Particle Swarm Optimization (PSO), Invasive Weed Optimization (IWO) and Imperialist Competitive Algorithm (ICA). In the first part, the study assessed, the effectiveness of various metaheuristic algorithms (PSO-IWO-ICA) in tuning the parameters of the ANN prediction structure in order to get the optimal parameter of the ANN. Whereas in the second part, once we extracted the best optimization algorithm, we combined it with the fuzzy logic technique and then we compared the effectiveness of the two techniques, ANN and Fuzzy logic. On the basis of root mean square error (RMSE), mean absolute error (MAE) and the coefficient of determination (R2), the proposed PSO-ANN and PSO-Fuzzy based models are compared with existing and recent models such as Ubic, Sidey, and Owolabi. The proposed PSO-Fuzzy model performs better than our PSO-ANN model, the Ubic, Sidey, and Owolabi models, with performance improvement of 70.90%, 90.36%, 89.74% 84.46%, respectively on the basis of RMSE. Similarly, it attains performance improvement of 71.26%, 90.31%, 89.58%, and 85.02% on the basis of MAE. Furthermore, the developed PSO-ANN based model outperforms the Ubic, Sidey and Owolabi models with performance improvement of 66.86%, 64.74% and 46.60% respectively, on the basis of RMSE and percentage enhancement of 66.27%, 63.75%, and 47.90% when compared on the basis of MAE. Although the PSO-Fuzzy model has the best performance of all the compared models, the developed PSO-ANN based model possesses the advantage of easy implementation in addition to its moderate performance.

Thiocyanate-Stabilized Pseudo-cubic Perovskite CH(NH2)2PbI3 from Coincident Columnar Defect Lattices.

α-FAPbI3 (FA+ = CH(NH2)2+) with a cubic perovskite structure is promising for photophysical applications. However, α-FAPbI3 is metastable at room temperature, and it transforms to the δ-phase at a certain period of time at room temperature. Herein, we report a thiocyanate-stabilized pseudo-cubic perovskite FAPbI3 with ordered columnar defects (α'-phase). This compound has a √5ap × √5ap × ap tetragonal unit cell (ap: cell parameter of primitive perovskite cell) with a band gap of 1.91 eV. It is stable at room temperature in a dry atmosphere. Furthermore, the presence of the α'-phase in a mixed sample with the δ-phase drastically reduces the δ-to-α transition temperature measured on heating, suggesting the reduction of the nucleation energy of the α-phase or thermodynamic stabilization of the α-phase through epitaxy. The defect-ordered pattern in the α'-phase forms a coincidence-site lattice at the twinned boundary of the single crystals, thus hinting at an epitaxy- or strain-based mechanism of α-phase formation and/or stabilization. In this study, we developed a new strategy to control defects in halide perovskites and provided new insight into the stabilization of α-FAPbI3 by pseudo-halide and grain boundary engineering.

Ground-State Surface of All-Inorganic Halide Perovskites

All-inorganic halide perovskites CsPbX3 (X = Cl, Br, and I) are attracting intensive attention for their outstanding optoelectronic properties and good stability. Surface energy plays a vital role in determining surface-related properties and phenomena, such as surface stability, equilibrium crystal shape, and the nucleation and growth of materials. There is a lack of thorough understanding of the surface energies and surface stability of CsPbX3. Here, we systematically explore these properties of CsPbX3 using first-principles calculations. We first deal with the convergence issue about the surface energy of the X-terminated (110)c surface of the cubic phase. By avoiding artificial octahedral tilts, we obtain convergent surface energy for the X-terminated (110)c surface from a view of pseudo-cubic perovskites. We then create stability phase diagrams and identify the ground state of CsPbX3 surfaces. The effects of octahedral tilts on the surface energies and the stability are evaluated by making a comparison of the surface energies between cubic and orthorhombic phases. Notably, we obtain the absolute surface energies of halide perovskites, which are difficult to be accessed from experiments. Our results can be a basis for further understanding and exploring the properties of passivated surfaces by ligands in all-inorganic halide perovskites.

Photoluminescence effects and probing phase transition of Sm3+-doped Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3 phosphor prepared by hydrothermal method

A series of [(Ba(1-0.3y)Ca0.3y)1-xSmx][Ti(0.8+0.2y)Hf(0.2-0.2y)]O3 (Sm3+-doped (1-y)Ba(Ti0.8Hf0.2)O3-y(Ba0.7Ca0.3)TiO3, abbreviated as Sm3+-doped BCTH, or (1-y)BHT-yBCT:xSm3+, x = 0.0005–0.03, y = 0.2–0.7, y representing the mole fraction of (Ba0.7Ca0.3)TiO3) nano phosphors were prepared by a hydrothermal method. The Sm3+ ions doping amount and triple-point morphotropic phase boundary (TMPB) composition dependent photoluminescence properties were systematically investigated. The hydrothermal synthesized powders present rather pure pseudo-cubic perovskite phase structure at room temperature and locate on the rhombohedral side of MPB. Under the excitation of 409 nm light, the powders exhibit dominant orange-red emission peaks with characteristic emission of the Sm3+ ions at around 564 nm, 596 nm, 644 nm, and 703 nm, relating to the transitions of 4G5/2 → 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The BHT-0.5BCT:0.005Sm3+ powder exhibits optimal emission in these Sm3+-doped BCTH powders. Furthermore, the phase transition temperature can be characterized by the multi-feature changes of the temperature dependent fluorescence intensity.

Enhanced energy storage properties and excellent fatigue resistance of Pb-free Bi0.47Na0.376K0.094Ba0.06Nb0.024Ti0.97−x(Ta0.24Sn0.7)xO3 relaxor ceramics

Pb-free Bi0.47Na0.376K0.094Ba0.06Nb0.024Ti0.97−x(Ta0.24Sn0.7)xO3 perovskite ceramics were prepared using a mixed-oxide reaction technique, and their structural, dielectric, ferroelectric, and energy storage properties were systematically investigated. All the compositions exhibited a pseudo-cubic perovskite crystal structure with a highly dense morphology. The doping of complex ions (Ta0.24Sn0.7)4+ disturbed the long-range ordering, which reduced the ferroelectric-to-relaxor phase transition temperature to room temperature. Hence, the modified ceramics exhibited relaxor behavior in their polarization and current density versus applied field plots. Owing to the excellent field-induced ferroelectricity and facile reversibility of ferroelectric-relaxor phase transition of polar nanoregions (PNRs), a high recoverable energy density of 1.65 J/cm3 with a good efficiency of 77.69% was achieved under 125 kV/cm at x = 0.03. In addition, the ceramic with x = 0.03 showed a high recoverable energy density of 1.01 J/cm3 with a high conversion efficiency of 84.22% at 70 °C under 80 kV/cm and fatigue-free characteristics during 105 cycles, demonstrating the highly dynamic and very stable nature of PNRs and very few ionic defects in the grains. Therefore, such ceramics (x = 0.03) are expected to be suitable for high-energy-density materials in electronic industries.

Dielectric properties and relaxor behavior of (1-x)Ba(Zr0.15Ti0.85)O3 - xBa(Mg(1⁄3)Nb(2⁄3))O3 ceramics for capacitor applications

The Ba(Zr0.15Ti0.85)O3 (BZT) ceramics were fabricated by the conventional solid-state method and the impact of Ba(Mg(1/3) Nb(2/3))O3 (BMN) addition into the BZT matrix on their microstructure, dielectric and ferroelectric properties were examined. According to the XRD analysis, the (1-x)Ba(Zr0.15Ti0.85)O3-xBa(Mg(1⁄3)Nb(2⁄3))O3 ceramics retain a pseudo-cubic ABO3 perovskite structure with an apparent decrease in c/a ratio as x increases. The SEM images show that the BZT-BMN ceramics instigate the reduction of the average grain sizes. And as the BMN content increases to 0.01, the Mg2+ and Nb5+ ion substitutions in the B-sites greatly improved the dielectric constant of BZT ceramics at room temperature. The frequency dispersion of the dielectric constant and the diffuseness of phase transition for BZT-BMN ceramics are enhanced by increasing the BMN addition. In the modified BZT ceramics, the dielectric maximum temperature (Tm) is reduced as the BMN content increases, and the temperature stability of the permittivity is modified by BMN addition. The hysteresis loop grows thinner and the remnant polarization, as well as coercive field, is greatly reduced as the BMN addition increases.

Tuning of high-temperature dielectric properties in the system (Bi0.5Na0.5)TiO3–BaTiO3–CaZrO3

Solid solutions of the (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xCaZrO3 system are regarded as promising dielectrics for high-temperature capacitors as they exhibit a remarkable flat trend of the permittivity over a large temperature range coupled with comparable low dielectric losses. In this work, the composition 0.8(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.2CaZrO3 was chosen in an attempt to optimize especially the high-temperature dielectric properties above 200 °C. In particular, the influence of excess bismuth to account for element losses caused by evaporation, and the effect of manganese as acceptor dopant are reported. Conventional solid-state reaction route was used to synthesize selected compositions. X-ray diffraction was used to confirm a pseudo-cubic perovskite main phase in all examined compositions, although small traces of a zirconia secondary phase were also detected. All samples exhibit an expected flat trend of the relative permittivity with a maximum deviation of the permittivity lower than 15% between −80 °C and 300 °C. The unmodified base composition shows small dielectric loss (<2%) between −55 °C and 265 °C. By using small quantities of manganese doping, the small-loss temperature range was extended (−70 °C and 300 °C). Excess bismuth also affects the temperature-dependent dielectric losses, resulting in a narrowed temperature range, eventually limiting the application possibilities.

Enhanced energy storage performance in (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 relaxor ceramics

Producing dielectric ceramics with favorable energy storage density, efficiency, and thermal stability has become an urgent task for developing energy storage devices. In this work, the innovative Pb-free (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 [(1-x)BSF-xCSTZ, x = 0.0, 0.1, 0.2, 0.3 and 0.4] ceramics were fabricated via traditional solid phase sintering approach. Their structures, electrical characteristics, and energy storage properties were researched comprehensively. The results verified that all the samples form solid solutions with pseudo-cubic perovskites structure. The density of ceramic samples is improved accompanied by gradually refined grain size upon increasing the CSTZ doping content. Interestingly, an excellent recoverable density of ∼3.3 J/cm3 with high efficiency of ∼78% is received at x = 0.3 under the average breakdown electric field of 350 kV/cm. The energy storage performances remained stable in a broad temperature range of 20 – 110 ℃, a large frequency range of 1 Hz – 1 kHz, and beyond 105 repeated charging-discharging cycles. The enhanced energy storage performances of BSF ceramics by introducing CSTZ result from the improved relaxor behavior and the increased electric breakdown strength. Our strategy for relaxor modulation with a sealed sintering method to achieve high energy storage performance can be valuable in BiFeO3-based ceramic capacitors.

Solution processing of morphotropic phase boundary BiFeO3‐PbTiO3 thin films with reduced conductivity for high room temperature switchable polarization

AbstractThe (1 – x)BiFeO3‐xPbTiO3 (BFO‐PTO) perovskite solid solution has great potential for being used in practical devices, as it exhibits significant ferroelectric response at its morphotropic phase boundary (MPB). However, the significant conduction, particularly high electrical leakage currents that BFO‐PTO films show at room temperature, deteriorates their functionality. This is mainly associated with the presence of multivalent iron along with A‐site and oxygen vacancies. Here, solution‐derived BFO‐PTO thin films have been crystallized at low temperature on Pt/TiO2/SiO2/Si substrates, by a rapid thermal annealing process to minimize Bi and Pb volatilization. X‐ray analyses have revealed that textured films are obtained with a pseudocubic perovskite structure and without the formation of detectable second phases. Microstructural studies indicated a columnar growth of the films with grain size well above the nanometric range, which, therefore, should not produce an appreciable reduction of the ferroelectric response due to size effects. Because of the relatively low content of charged defects produced in these BFO‐PTO films during processing, ferroelectric hysteresis loops can be measured at room temperature. The highest value of remnant polarizations (2PR = 58 μC/cm2) was obtained for the 0.65BiFeO3‐0.35PbTiO3 (65BFO‐35PTO) films, which suggests that this film composition lies in the proximity of the MPB where the coexistence of a highly textured &lt;100&gt; tetragonal phase and a rhombohedral one seems to occur.

High-Temperature Synthesis and Dielectric Properties of LaTaON2.

The development of new synthetic methodologies of perovskite oxynitrides is challenging but necessary for the search of new compounds and the investigation of new properties. Here, we report a new method of preparation of the perovskite LaTaON2 that has been investigated as a pigment and photocatalyst for water splitting. The synthesis proceeds through the solid-state reactions under N2 at 1500 °C between La2O3, LaN, and Ta3N5 or between LaN and TaON, which are completed after 3 h and lead to sintered, highly crystalline samples with particle sizes up to 1 μm. Nitrogen-deficient samples LaTaO1+xN2-x with x ≤ 0.35 are prepared by changing the N/O ratio in the mixture of reactants. Electron diffraction, synchrotron diffraction, and neutron diffraction studies on stoichiometric and nitrogen-deficient compounds indicate that they crystallize in the monoclinic space group I2/m with lattice parameters for LaTaON2 of a = 5.71458(7), b = 8.05987(10), c = 5.74772(6) Å, and β = 89.982(3)°. The three anion sites of the I2/m structure are partially occupied by oxygen and nitrogen, with a preference of nitride for two positions with occupancies of 77 and 88%. This anion distribution is different from that reported in previous studies of samples prepared by ammonolysis at lower temperature, suggesting that the synthesis conditions affect the anion order of this perovskite. Optical measurements indicate a band gap of about 1.9 eV, which is close to that observed in samples prepared by other methods. The determined dielectric permittivity for LaTaON2 εr ≈ 200, reported for the first time for a highly nitrided pseudocubic perovskite, is similar to that observed in perovskites with one nitrogen per formula.

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Wide-Range Epitaxial Strain Control of Electrical and Magnetic Properties in High-Quality SrRuO3 Films

Epitaxial strain in 4d ferromagnet SrRuO3 films is directly linked to the physical properties through the strong coupling between lattices, electrons, and spins. It provides an excellent opportunity to tune the functionalities of SrRuO3 in electronic and spintronic devices. However, a thorough understanding of the epitaxial strain effect in SrRuO3 has remained elusive due to the lack of systematic studies. This study demonstrates wide-range epitaxial strain control of electrical and magnetic properties in high-quality SrRuO3 films. The epitaxial strain was imposed by cubic or pseudocubic perovskite substrates having a lattice mismatch of -1.6 to 2.3% with reference to bulk SrRuO3. The Poisson ratio, which describes the two orthogonal distortions due to the substrate clamping effect, is estimated to be 0.33. The Curie temperature (TC) and residual resistivity ratios of the series of films are higher than or comparable to the highest reported values for SrRuO3 on each substrate, confirming the high crystalline quality of the films. A TC of 169 K is achieved in a tensile-strained SrRuO3 film on the DyScO3 (110) substrate, which is the highest value ever reported for SrRuO3. The TC (146-169 K), magnetic anisotropy (perpendicular or in-plane magnetic easy axis), and metallic conduction (residual resistivity at 2 K of 2.10 - 373 {\mu}{\Omega}cm) of SrRuO3 are widely controlled by epitaxial strain. These results provide guidelines to design SrRuO3-based heterostructures for device applications.

The role of Co substitution in the structural characteristics and magnetic properties of La2CoxNi1-xMnO6 epitaxial film

Novel La2CoxNi1-xMnO6 (LCxNMO, x = 0–0.4) thin films were prepared by pulsed laser deposition, and the influences of Co-doping content on the crystallographic structure, chemical structure as well as magnetic property were studied. The AFM and SEM images revealed a uniform film growth and smooth surfaces for all the films. The (HR)XRD analysis and their RSM results testified for the formation of pseudocubic perovskite films epitaxially grown onto LAO(00l) substrate. The in-plane lattice parameter increased with increasing proportion of Co substituting for Ni sites, as expected due their ionic radii differences. In our work, a change of Mn3+ + Ni3+/Co3+ → Mn4+ + Ni2+/Co2+ was found, and the mechanism in the enhancement of the magnetic property was demonstrated. It proposed that the performances of all the films can be enhanced and regulated by controlling the Co-doping content. Among all the films, LC0.2NMO film possessed the maximum Mn4+ ion concentration (80%) and displayed the highest B-site ordering degree. As a consequence, LC0.2NMO was achieved to exhibit a high Curie temperature (278.4 K) and the best saturation magnetization (513.72 emu/cm3), on account of the combined effects of the strong B-site cation ordering and the structural distortion after Co-doping.

Narrow bandgap ferroelectric semiconductors within BiFeO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;-based solid solution perovskites

<p indent=0mm>Solar energy is a clean and renewable source of energy. Various solar photovoltaic (PV) cell technologies have been developed, out of which perovskite PV cell technology is growing rapidly. Using organometal halide perovskite as an optical absorption component, the power conversion efficiency (PCE) of heterojunction solar PV cells increased from 3.8% in 2009 to 25.5% recently. Nonetheless, the bottleneck for CH₃NH₃PbI₃-based solar cells entering into commercial market is their poor stabilities relating to environmental, thermal, and ultraviolet light influence. In contrast, transition metal oxide perovskites are thermodynamically and chemically stable enough for solar cells’ commercialization, with more advantages such as bandgap (<italic>E</italic>_g) adjustability from <sc>0 to 6 eV,</sc> processing being compatible with transparent conducting oxides, and ferroelectric bulk PV effect. Owing to a wide <italic>E</italic>_g, traditional ferroelectric perovskite oxides exhibit poor visible optical absorption, low electrical conductivity, and thus extremely low PCE. As an alternative to p-n junction PV effect, ferroelectric bulk PV effect provides a new separation mechanism for photo-excited carriers, which is closely related to spatial inversion symmetry breaking and its resulting spontaneous electric polarization. Different from p-n junction, the active space for photo-excited carrier separation spans the whole ferroelectric body, and thus an above-<italic>E</italic>_g open-circuit voltage is produced. By narrowing <italic>E</italic>_g while maintaining ferroelectricity of oxide perovskites, ferroelectric semiconductors become available to monolithically integrate the p-n junction and ferroelectric bulk PV effects, which could, in principle, go beyond the Shockley-Queisser theoretical PCE limit of conventional<italic> </italic>p-n junction solar cells. Bismuth ferrite (BiFeO₃) has been experimentally demonstrated to exhibit ferroelectric PV effect. Meanwhile, it has a high ferroelectric Curie temperature (<italic>T</italic>_C) of 830°C and an intermediate <italic>E</italic>_g of <sc>~2.2 eV,</sc> providing a large chemical space for solid solution perovskite oxides to trade off both target properties of narrow <italic>E</italic>_g and <italic>T</italic>_C><sc>400 K.</sc> In this report, 0.50BiFeO₃-0.25A₁MnO₃-0.25A₂TiO₃ (A₁ = Ca, Sr, Ba, A₂ = Sr, Ba, Pb) and 0.49BiFeO₃-0.26BaTiO₃-0.25(Sr₁₋_{<italic>x</italic>}Ba_{<italic>x</italic>})(Co_1/3Nb_2/3)O₃ (<italic>x </italic>= 0 and 0.4) ferroelectric semiconductors with <italic>E</italic>_g of <sc>~0.9 eV</sc> were created by substituting Fe³⁺ with Mn⁴⁺ or Co²⁺ in BiFeO₃-based solid solution perovskites. Ceramic samples were prepared using a refined solid-state reaction electroceramic processing. X-ray diffraction measurements showed them crystallized in a single pseudo-cubic perovskite phase, while Raman scattering characterizations illustrated a breaking of spatial inversion symmetry at room temperature. Optical absorbance measurements found that these Mn⁴⁺- or Co²⁺-substituted BiFeO₃-based solid solution perovskites have a direct bandgap in a range of <sc>0.75–1.0 eV.</sc> Compared with CH₃NH₃PbI₃ perovskites, their optical absorption reaches near-infrared band of solar spectra. Temperature-dependent resistance measurements showed their resistivity on the magnitude of order of <sc>~10⁶ Ω cm</sc> with thermal excitation energy (<italic>E</italic>_a) of <sc>~0.5 eV.</sc> Combined with observation of frequency-dependent dielectric properties, A-site vacancies were proposed responsible for electrical conduction and dielectric relaxation. Through data-mining causal relationships between <italic>E</italic>_g and the filling number of d electron of B-site cations, <italic>μ</italic>×<italic>r</italic>_A/<italic>r</italic>_B ensemble descriptor of oxide perovskites (<italic>μ</italic>, <italic>r</italic>_A, and <italic>r</italic>_B are the reduced mass of primitive cell, A-site cation radius, and B-site cation radius, respectively), a physical model was proposed to predictively design chemical compositions of ferroelectric semiconducting oxide perovskites with <italic>E</italic>_g<sc>~0.9 eV</sc> for applications of solar PV cells. This essay provides an opportunity for developing novel solar PV cells to integrate monolithically p-n junction and ferroelectric bulk PV effects, with PCE beyond the Shockley-Queisser theoretical limit.

Structure and enhanced dielectric temperature stability of BaTiO3-based ceramics by Ca ion B site-doping

Capacitor is an important part of many electronic devices, so the temperature stability as one key parameter of capacitor needs to be improved constantly for meeting the requirements of various application temperature. Here, combined with the X-ray diffraction (XRD), selected area electron diffraction (SAED) and Vienna Ab-initio Simulation Package (VASP) calculation, it was confirmed that Ca ion can substitute the Ti site in the BaTi1-xCaxO3-x [BTC100×] (0 ≤ x ≤ 0.05) ceramics synthesized by solid-phase method which greatly improved the low-temperature stability of dielectric constant. Moreover, introducing Bi3+ and Zn2+ into BTC4 to form (1-y)BaTi0·96Ca0·04O2.96-yBi(Zn0·5Ti0.5)O3 [(1-y)BTC4-yBZT] (0.1 ≤ y ≤ 0.2) ceramics can further improve the dielectric-temperature stability by means of diffused phase transition and core-shell structure. Most importantly, the 0.85BTC4-0.15BZT ceramics with a pseudocubic perovskite structure possessed a temperature coefficient of capacitance at 25 °C (TCC25°C) being less than ±15% over a wide temperature range of −55 °C–200 °C and a temperate dielectric constant (ε = 1060) and low dielectric loss (tanδ = 1.5%), which measure up to the higher standard in the current capacitor industry such as X9R requirements.

Improved electric energy storage properties of BT-SBT lead-free ceramics incorporating with A-site substitution with Na & Bi ions and liquid sintering generated by Na0.5Bi0.5TiO3

Due to the merits of high safety and easy preparation, dielectric ceramics have become key engineering materials for capacitors. Within this article, different contents of Na0.5Bi0.5TiO3 were introduced into Ba0.65Sr0.245Bi0.07TiO3 relaxor ferroelectric ceramics in order to increase the disorder degree of A-site ions in perovskite structure and modify the relaxation, which could generate liquid sintering promoting densification, then finally enhancing the dielectric energy store performance of ceramics. The research results show that all the bulk samples prepared through traditional processing route are exhibiting pseudocubic perovskite structure, and their surfaces are with Na0.5Bi0.5TiO3 (NBT)-rich phase formed during densification due to a relatively low sintering temperature of NBT. The relaxation coefficient of BT-SBT-0.01NBT ceramic is 1.8. Because of the existence of liquid phase formation during sintering, the dielectric breakdown strength (BDS) of BT-SBT-0.01NBT ceramic is increased to 230 kV/cm, and the recoverable energy density (Wrec) reached 2.22 J/cm3. The introduction of NBT can hence enhance the relaxation and BDS, finally elevate the energy storage performances.