B-site Ions Research Articles

Sintering behavior, lattice vibrational characteristics and dielectric properties of B-site ion substituted BaWO4 ceramics for LTCC applications

The influences of Mo6+ substitution at the B-site of scheelite structure on the sintering character, microstructures, lattice vibrational characteristics, and dielectric properties of BaW1-xMoxO4 (x = 0.10-0.30) ceramics were studied in detail in this paper. The sintering temperature of BaW1-xMoxO4 ceramics was effectively reduced to less than 950oC through forming a scheelite solid solution. The densification and the quality factor (Q×f) of BaW1-xMoxO4 ceramics were also enhanced compared with pure BaWO4 ceramic. Raman spectroscopy confirmed that the dielectric constant (εr) was highly correlated with molecular polarizability, and the Q×f was strongly dependent on the symmetric stretching bond of [WO4] tetrahedron. Oxygen bond valence was one of crucial parameters for modulating the temperature coefficient of resonant frequency (τf). Interestingly, the BaW0.75Mo0.25O4 ceramic sintered at 910oC exhibited favorable microwave dielectric properties of εr = 9.44, Q×f = 46,820GHz (@12.5GHz), and τf = −69.2 ppm/oC. Meanwhile, the BaW0.75Mo0.25O4 ceramic had stupendous dielectric properties in low-frequency band: εr = 17.5 and dielectric loss (tanδ) = 2.2×10-4 (@10MHz). In addition, there was good chemical compatibility between BaW0.75Mo0.25O4 ceramic and silver electrodes. These findings evidence that BaW1-xMoxO4 ceramics are competitive candidates in LTCC technology.

Anionic and cationic co-doping to enhance the oxygen transport property of Bi0.5Sr0.5FeO3-δ as a high-performance air electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) have attracted considerable interest due to their efficient energy conversion. However, the low catalytic activity of air electrodes limits the application of RSOCs. Bi0.5Sr0.5Fe0.9Ta0.1O3-δ developed in our previous work exhibits a comparatively desirable performance and is expected to be further optimized. Herein, a novel strategy of anionic F and cationic Ta co-doped Bi0.5Sr0.5Fe0.9Ta0.1O3-δ-xFx (x = 0, 0.05, 0.10, 0.15, denoted as, BSFTF0, BSFTF5, BSFTF10, BSFTF15) materials are obtained to enhance the oxygen transport property of Bi0.5Sr0.5FeO3-δ for RSOCs. The polarization resistance (Rp) of BSFTF10 (0.017 Ω cm2) decreases by 66 % compared with that of BSFTF0 (0.051 Ω cm2) at 800 °C. In fuel cell mode, the single cell with BSTF10 reaches the maximum power density of 908 mW cm−2, which is approximately 72 % higher than the only Ta-doped BSFTF0 (527 mW cm−2) at 800 °C. In electrolysis mode, the single cell with BSFTF10 exhibits a high electrolysis current density of 1679 mA cm−2, indicating an approximately 90 % increase compared to that of BSFTF0 at 800 °C and 1.5 V with 70 % CO2-30 % CO feed gas. The bulk chemical diffusion (Dchem) of BSFTF10 is up to 5.12 × 10−4 cm2 s−1, which is 4.3 times higher than that of BSFTF0. The superior oxygen transport property of BSFTF10 is attributed to the high electronegativity of F− (4.0) and low electronegativity of Ta5+(1.8), which may weaken the chemical bonding between B-site ions and O2−, generating more oxygen vacancies and accelerating the rate of oxygen transfer. The results indicate that F and Ta co-doping is an effective strategy to develop a highly catalytically active air electrode for RSOCs featuring oxygen transport properties.

Improved microwave dielectric properties of LaZn1/2Ti1/2O3 through Y3+ substitution

LaZn1/2Ti1/2O3 is a double perovskite with promising microwave dielectric properties for applications towards dielectric resonators and antennas. Its dielectric properties can be enhanced through the substitution of suitable ions in either A- or B-sites. In this paper, we report a significant improvement in the quality factor (Q) by substituting Y3+ in the La site with a marginal reduction in dielectric constant (εr). A single phase is confirmed in XRD indicating the formation of La1-xYxZn1/2Ti1/2O3 (0 ≤ x ≤ 0.25) solid solutions. The substitution results in an expansion of lattice along the b direction while there is a contraction in both a and c directions, leading to a reduction in unit cell volume. The dielectric constant, εr, is observed to reduce from 33.4 to 29.6 due to the polarizability of A-site atoms. The temperature coefficient of resonant frequency (τf) increases with an increase in x which does not appear to correlate with reducing tolerance factor (t). This non-conventional behaviour of τf in this perovskite based solid solutions brings bond valence of O site (VO) into picture. VO appears to show competing effect on τf. The non-monotonic behaviour is observed in Q×f with a maximum value of 41,400 GHz at x = 0.15 and a sharp decline for x > 0.15. This observation is correlated with variations in the A-site bond valence (VA) and a long-range ordering (LRO) of B-site ions. LRO is associated with Ag mode at 710 cm−1 in the Raman spectra. The low frequency (< 250 cm−1) Raman modes shift to a higher frequency with the increase in Y3+. Y3+ substitution also induces lattice distortion which is discussed in terms of variations in FWHM and relative intensity of the Raman modes.

SrCoO3-based perovskites with enhanced electrochemical performance through structural tailoring induced by B-site substitution

The progression of supercapacitor technology hinges on the discovery of high-performance electrode materials to enhance energy storage. SrCoO3-δ perovskite holds considerable promise potential as an anion intercalation electrode material. To elucidate the structural and electrochemical performance modulation rules of SrCoO3-based perovskites, this study synthesized SrCo0.875M0.125O3-δ (M = Ti, Ta, Nb, Fe) perovskites with different B-site ion substitutions. The structural tailoring induced by B-site substitution were thoroughly investigated alongside their corresponding electrochemical performance. Notably, SrCo0.875Ti0.125O3-δ exhibited a simple cubic structure, while the other samples displayed a tetragonal structure. Additionally, SrCo0.875Fe0.125O3-δ displayed numerous oxygen vacancies and significant distortion in the [CoO6] octahedron, which is attributed to the lower valence state of Fe. At a current density of 1 A g−1, the specific capacities of SrCo0.875M0.125O3-δ (M = Nb, Ti, Fe, Ta) perovskites were 984.43, 853.33, 503.53, and 452.00C/g, respectively. SrCo0.875Nb0.125O3-δ demonstrated the highest specific capacity and capacity retention rate across various current density, owing to its relatively stable structure with appropriate oxygen vacancies and multivalent state changes of Nb. In contrast, SrCo0.875Fe0.125O3-δ, with excessive oxygen vacancies and severe structural distortions, exhibited restricted electrochemical performance, particularly at higher current densities. Integrating structural and performance analysis, this work proposes an optimization strategy for the electrochemical performance of SrCoO3-δ-based perovskite electrode materials, emphasizing the importance of tailoring multivalent B-site elements to achieve a stable perovskite structure with appropriate oxygen vacancies.

A series of Ba12M0.5Zr0.5Nb9O36 (M=Ni, Mg, Co, and Zn) microwave dielectric ceramics with hexagonal perovskite structure

A series of hexagonal perovskite Ba12M0.5Zr0.5Nb9O36 (M = Ni, Mg, Co, Zn) ceramics were prepared by solid-state reaction method. XRD and Rietveld refinement results showed that all ceramic samples belong to the hexagonal perovskite structure with R-3m space group. With different B-site ion substitution, variation of permittivity (εr) can be ascribed to the average ion polarizability. Ceramics with highest relative density exhibit maximum quality factor (Q×f) values. Among all samples, the optimal microwave dielectric properties of εr = 35.2, Q×f = 57,985 GHz, and τf = 26.4 ppm/°C for Ba12Mg0.5Zr0.5Nb9O36 were obtained, which indicated that Ba12Mg0.5Zr0.5Nb9O36 ceramic is a candidate material for microwave communication applications.

Observation of the multiple magnetic phases in double perovskite Pr1.8La0.2CoFeO6

The structural and magnetic properties of the double perovskite Pr1.8La0.2CoFeO6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism withTN ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (TG ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; HSEB∼ 1.8 kOe and giant conventional exchange bias, HCEB∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below TN, clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly.

Effect of A and B-site ion doping on the structure and properties of KNN-based ceramic coatings

K0.5Na0.5NbO3 (KNN) ceramics have been widely studied for high Curie temperature (Tc) and good electrical properties. The structural and electrical properties of KNN ceramics were significantly improved by A-site and B-site doping modifications. In this paper, KNN-based ceramic coatings doped with Mn, and Sb were prepared by supersonic plasma spraying. The effects of doping ions at A-site and B-site on the microstructure, phase structure, mechanical properties, and electrical properties of KNN-based ceramic coatings were mainly analyzed. The results show that the surface of the three coatings KNN, K0.5Na0.5Nb0.94Sb0.06O3 (KNNS), and K0.49Na0.49Mn0.02NbO3 (KNMN) is relatively flat, uniform distribution of the elements. The surface roughness (Sa) is 3.85 μm, 3.88 μm, and 3.66 μm, respectively. Pores and cracks are present within the coatings, but the KNNS ceramic coatings have significantly fewer pores and cracks compared to the KNN and KNMN ceramic coatings. XRD results show that KNN-based ceramic coatings exhibit single perovskite structure, and both Mn and Sb are successfully introduced into the KNN ceramics without the generation of a second phase. XPS results showed that the valence states of the elements in the KNN ceramic coatings did not change. In KNMN and KNNS ceramic coatings, the valence state of the doped elements did not change. The addition of Mn2+ and Sb3+ reduced the oxygen vacancy in KNN ceramic coatings. Among them, the KNMN ceramic coatings microhardness increased by 45.3 HV0.2, remnant polarization (Pr) increased by 8.1 μC/cm2, the dielectric constant (εr) increased by 107, and dielectric loss greatly reduced, reaching 0.005. The KNMN ceramic coatings microhardness increased by 90.8 HV0.2, dielectric constant increased by 195, Pr increased by 16.7 μC/cm2, dielectric loss is 0.007. These findings demonstrate that doping with Mn2+ and Sb3+ has a positive impact on the performance of KNN ceramic coatings, with Sb3+ having a greater effect.

La-Co-Mn perovskite (LCMO) for NO and Hg0 oxidation: Experimental and DFT investigations of adsorption processes

To achieve superior catalytic performance, the development of plausible regulation of pure perovskite structure is necessary, which has become a hot research topic. In this study, manganese (Mn) ions were employed to dope cobalt (Co) ions at the B-site of LaCoO3, yielding a series of LaCo1-xMnxO3 (x = 0.1–0.5) perovskite (LCMO). The oxidation activity of NO and Hg0 was conducted, evaluating the effect of Mn-doping. The results indicated a minor change in NO oxidation activity and a significant enhancement in Hg0 oxidation, reaching above 92% at 100°C–300°C for LCMO. Structural characterization revealed a gradual transition in the phase structure of LCMO from the R-3C diamond phase to the Pm-3m cubic phase with increasing Mn doping. Furthermore, electronegativity properties of LCMO evolved with Co ions at the B-site exhibiting a preference for generating Co2+ over the more active Co3+. Finally, DFT calculations were conducted to analyze the adsorption energies of NO and Hg0 at different active sites on the surfaces of LaCoO3 (110) and Mn-LaCoO3 (110). The results indicated that Mn doping increased the active site amounts and strengthened the adsorption energy of Hg0 on the Mn-LaCoO3 (110) surface. However, the adsorption energy of NO remained largely unchanged, validating the oxidation results. This study offered insights for selecting B-site ions to adjust the perovskite structure of excellent performance, facilitating its industrial application.

Study of the cationic substitution effect on the magnetic properties of the ferrite MnxZn1-xFe2O4 nanoparticles prepared by TREG-mediated solvothermal route

MnxZn1-xFe2O4 (x = 0–1) solid solution was prepared using the TREG-mediated solvothermal method. 10–12 nm spherical superparamagnetic particles (except for ZnFe2O4) were obtained. At room temperature, the ferrites have lower magnetic saturation (Ms) than magnetite. However, at 10 K, it is precisely the opposite. DRX and EXAFS showed that incorporating Zn2+ ions in tetrahedral A-sites provokes a redistribution of Mn and Fe ions in octahedral B-sites of the mixed spinel structure. For Zn concentrations from x = 0.5 and below, the Mn and Fe ions are almost equally distributed between A and B-sites. Therefore, at low Zn concentrations, the small migration of Fe and Mn ions to B-sites increases the magnetic moment of B sub-lattices and, consequently, the total magnetic saturation. In addition, Mn2+ oxidized to Mn3+ and, simultaneously, Fe3+ reduced to Fe2+, affecting the magnetic properties. The increment of Zn concentration severely reduces the magnetization.

Accelerating the discovery of direct bandgap doped-spinel photovoltaic materials: A target-driven approach using interpretable machine learning

The spinel structure, unifying tetrahedral and octahedral coordination within a single crystal lattice, emerges as a promising alternative to perovskite and traditional semiconductors, particularly in the context of photovoltaic applications. However, the majority of surveyed spinels exhibit an indirect bandgap, imposing substantial limitations on their utility. Consequently, doping is required to tailor indirect bandgap spinels into direct ones. In this study, leveraging machine learning (ML) algorithms, we design a target-driven framework to accelerate the ab initio predictions of unknown doped-spinels using elements from the periodic table. Utilizing this approach, we have introduced a novel machine learning classification model designed for the prediction of the direct-indirect bandgap nature in spinel materials. This pioneering model shows promising potential for achieving rapid and precise predictions, particularly in scenarios involving small dataset. Especially, a full list of potential 3449 (AxA′1-x)B2X4-type doped-spinels and 3809 A(BxB′2-x)X4-type doped-spinels with direct bandgaps is identified from the vast pool of unknown doped-spinel materials. Further, the application of interpretable ML extracts the first ionization energy of the B-site ion as the most important feature for the nature of bandgap, offering insightful design rules. This research provides a novel perspective on unraveling spinel materials, and the proposed design framework proves effective in identifying high-performance materials within a vast chemical space, all while minimizing computational costs.

Promotion of Acid-Water Oxidation by Lattice Distortion and Orbital Hybridization Induced by Ionic Dopant in Pyrochlore Y2Ru2O7.

For acid-water oxidation, pyrochloric ruthenates are thought to be extremely effective electrocatalysts. In this work, through partial B-site replacement with larger M2+ cations, the electronic states of Y2Ru2O7 with strong electron correlations are reasonably managed, by which the inherent performance is tremendously promoted. Based on this, the improved Y2Ru1.9Sr0.1O7 electrocatalyst exhibits an outstanding durability and presents a highly inherent mass activity of 1915.1 A gRu-1 (at 1.53 V vs RHE). The enhanced oxygen-evolving reaction (OER) activity by ionic dopant in YRO pyrochlore can be attributed to two aspects, i.e., the lattice distortion induced inhibition of the grain coarsening, which results in a large surface area for YRO-M and increases the OER active sites, and the weakening of electron correlation via broadening of the Ru 4d bandwidths due to the increase of the average radius of B-site ions, which gives rise to an enhancement of conductivity and a strengthened hybridization between Ru 4d and O 2p orbitals and improves the reaction kinetics. The synergistic effects of lattice distortion and orbital hybridization promote the enhanced OER activity. The results would provide fresh concepts for the design of improved electrocatalysts and underscore the significance of managing the intrinsic performance through the dual modification of microstructure morphology and electronic structure.

Effects of heterovalent ions doping-induced oxygen octahedral distortion and defect chemical change on piezoelectric characteristics and thermal stability of PHT-PIN ceramics

Electromechanical devices require functional materials possessing excellent piezoelectric properties, good thermal stability, and high electromechanical coupling coefficients. To modulate the piezoelectric, dielectric, and electromechanical characteristics of 0.89Pb(Hf0.47Ti0.53)O3-0.11Pb(In1/2Nb1/2)O3 (PHT-PIN) piezoelectric ceramics, heterovalent ions of lithium (Li) and tungsten (W) were doped through a traditional solid-phase reaction approach. On the one hand, large lattice distortions caused by the doped W6+ resulted in the shortening of BO bonds while an increase in the local displacement of B-site ions. Moreover, a mismatch occurred for the oxygen octahedral dimensions, and a subsequent disruption of the long-ranged ordered ferroelectric domains was observed, which resulted in the formation of microdomains. On the other hand, the changes in the concentration of oxygen vacancy defects induced by the Li and W doping inside the ceramic were comprehensively analyzed. The decrease in the concentration of oxygen vacancies was found to be accompanied by the enhancement of piezoelectric properties of the material. Excellent comprehensive performance (piezoelectric coefficient d33 = 655 pC N−1, Curie temperature Tc = 321.1 °C, dielectric constantεr = 3352.31, electromechanical coupling coefficient kp = 0.67, and residual polarization strength Pr = 55 μC cm−2) was obtained for 0.2 mol % doping amount of Li+ and W6+ ions. This work, therefore, proposes a novel strategy for the origin of piezoelectric properties and inspires doping of other heterovalent ions to improve the piezoelectric properties of ceramics. It further promotes the development of Pb-based piezoelectric ceramics for electromechanical devices that can efficiently operate under high-temperature environments.

Effect of A-site and B-site ion substitution on the electrical and thermoelectric properties of nanostructured perovskite CaMnO3

Effect of A-site and B-site ion substitution on the electrical and thermoelectric properties of nanostructured perovskite CaMnO3

B-site ion regulation strategy enables performance optimization and multifunctional integration of hybrid perovskite ferroelectrics

B-site ion regulation strategy enables performance optimization and multifunctional integration of hybrid perovskite ferroelectrics

Atomic insights into the optoelectronic properties of vacancy-ordered double perovskite halide semiconductors

Vacancy-ordered halide perovskite Cs2BX6 semiconductors are attracting an increasing level of interest for optoelectronic applications due to their high chemical stability and unique light emission properties. Here, we performed first-principles calculations to determine the energy positions and atomic orbital hybridization features of band edge states in Cs2BX6 (B = Ge, Sn, Te, Ti, Zr, Hf; X = Cl, Br, I). Our results revealed that all the Cs2BX6 perovskites, except for Cs2TeX6, have direct bandgaps at the Γ point. The indirect bandgaps of Cs2TeX6 originate from the symmetry-forbidden Te p–X p coupling at the Γ point. Both energy positions and dispersions of the band edge states of Cs2BX6 can be well modulated by varying X- and B-site ions. Our work provides a comprehensive understanding of electronic structures and optoelectronic properties of Cs2BX6 perovskites, shedding light on the design rules for high-performance perovskite optoelectronics.

Enhanced ferromagnetic properties achieved by F-doping in BaFe1-xMnxO3-δ.

Tailoring the crystal structure, spin, and charge state of perovskite oxides through fluorine ion doping is an attractive and effective strategy, which could significantly modify the physical and chemical properties of base oxides. Here, BaFe1-xMnxO3-δ (x = 0, 0.1, 0.2, 0.3) and BaFe1-xMnxO2.9-δF0.1 (x = 0.1, 0.2, 0.3), belonging to 6H-type BaFeO3-δ, are prepared and investigated to evaluate the impact of F- doping. The distortion of crystal structure and the reduced average valence of Mn and Fe confirm the preference for F- substitution in the hexagonal layer, which are found as the key factors for the improved magnetic properties, including ferromagnetic ordering temperature, coercive force, and remanent magnetization. Moreover, the valence reduction of B-site ions and the increased resistance distinctly indicate the expense of electron hole via fluorine doping. This work describes the adjustment of crystal structure, electronic configuration, and ferromagnetic performance by simple F- doping, which provides a prospect for practical magnetic materials.

Simultaneous enhancement of piezoelectric properties and Curie temperature in BiFeO3–BaTiO3 lead-free ferroelectrics via simple B-site modification

The simultaneous enhancement of d33 and Tc was achieved in BF–BT by simple B-site doping.

Phonon mode and dielectric function dynamics of Bi0.5Na0.5TiO3-xSm2Ti2O7 ceramics during the phase transitions discovered by Raman scattering and spectroscopic ellipsometry

Recently, Bi0.5Na0.5TiO3-based ceramics have drawn widespread attention due to their excellent energy storage properties. Here, a comprehensive analysis of the composition- and temperature-driven transition processes in (1 − x)Bi0.5Na0.5TiO3-xSm2Ti2O7 (BNST-x) polycrystals have been presented using Raman scattering and spectroscopic ellipsometry. With increasing Sm2Ti2O7 content, BNST-x ceramic gradually becomes disordered and belongs to the superparaelectric state at x = 0.12 near room temperature. Moreover, the thermal evolution of the lattice kinetic behaviors shows two crucial temperatures: the depolarization temperature Td and the temperature at the maximum dielectric permittivity Tm, which suggest the transitions from nonergodic relaxor ferroelectric—ergodic relaxor (ER) ferroelectric and ER ferroelectric—superparaelectric, respectively. It is noteworthy that the series of changes is closely related to the ordering degree of the B-site ion affected by the doping and the temperature. This work gives an insight into the connection among the phonon behavior, electronic transition, and lattice structure of BNST-x ceramics, which can further understand the phase transition mechanisms under the doping and thermal field.

Atomic‐scale insights into electronic, structural, dielectric, and ferroelectric properties of Ba(Zr, Ti)O3 perovskites

Ba(Zr, Ti)O3 perovskites are promising lead-free piezoelectric and relaxor ferroelectric materials for energy storage and harvest devices, of which the ferroelectric mechanism has long been ambiguous. We theoretically investigated the ferroelectric mechanism from the electronic and atomic scale using first-principles calculation based on density functional theory and density functional perturbation theory. With increasing zirconium content, it is obtained a lattice expansion and a decrease in the ferroelectric polarization in agreement with experiment. An unstable zone-center phonon mode is observed in the polar ferroelectric phase, which tends to stabilizein the nonpolar paraelectric phase, which is associated with the engineering of the relative displacement of the B-site ions that alters the short-range force. The newly formed Ti/Zr (dzx,dyz)-O (2px,2py) π-type bonds are discovered to be the origin of the Ba(Zr, Ti)O3ferroelectric instability and polarization. Local relaxation strains caused by lattice misalignment of the ionic displacements of Ti ions and Zr ions suppress the polarization of Ba(Zr, Ti)O3 by counteracting the off-centering of Ti ions and adjacent Zr ions in certain directions.

Optimized Electrocaloric Refrigeration in Lead-Free NaNbO3-Based Ceramics via AFE ↔ FE Phase Transition Modulation.

An outstanding challenge for eco-friendly ferroelectric (FE) refrigeration is to achieve a large adiabatic temperature change within a broad temperature range originating from the electrocaloric (EC) effect, which is expected to be realized in antiferroelectric (AFE) materials owing to the large entropy change during electric field and thermally induced phase transition. In this work, a large EC response over a wide response temperature range can be achieved slightly above room temperature via designing the phase transition of NaNbO3. An irreversible to reversible AFE-FE phase transition on heating induced by the introduction of CaZrO3 into NaNbO3 plays a key role in the optimized electrocaloric refrigeration. Accordingly, accompanying the local structure transformation corresponding to the B-site ions, the transition temperature between the square polarization-electric field (P-E) hysteresis loop (the irreversible AFE-FE phase transition induced by the electric field) and the repeatable double P-E hysteresis loop (the electric field induced reversible AFE-FE phase transition) was tailored to around room temperature, in favor of extending large entropy change to the wide temperature range. This work provides an efficient approach to designing lead-free EC materials with excellent EC performance, promoting the advancement of environmentally friendly solid-state cooling technology.