Barium Stannate Research Articles

Efficient light harvesting using simple porphyrin-oxide perovskite system

Here, we report the systematic studies on photoanodes of phase pure polycrystalline microrods of Barium Stannate (BaSnO3) microrods for application in porphyrin dye-sensitized solar cell (DSSC). We were able to establish the effect of vacuum annealing on BaSnO3 thin films on its electrical, optical and adsorption properties using XPS, UV–Vis, photoluminescence and adsorption isotherm studies. Increase in oxygen vacancy with annealing is found to increase the room temperature (RT) electron mobility from 49.1 to 82.4 cm2/V sec whereas macroporous nature of samples were found suitable for faster dye adsorption (~ 30 min). Post TiCl4 treatment studies, the maximum efficiency (η) of 4.7% is achieved in BSO films with current density Jsc ~ value as 10.4 mA/cm2; whereas DSSC fabricated using annealed BSO films gave maximum efficiency of 6.1% with Jsc value as 12.2 mA/cm2, during which the value of FF increased from 73.4 to 81%. The IPCE and proposed electron transfer mechanism suggested the potential application of macroporous BSO with unconventional dyes such as metallised-porphyrin. Our results strengthen the idea of using phase-pure, visible transparent porous BSO nanostructures with induced oxygen vacancies due to annealing process post-synthesis which eventually increased DSSC performance from by 84%.

Influence of synthesis methods on the microstructure and Ethanol Sensing properties of barium stannate

Herein, we report the synthesis of BaSnO3 (BSO) from molten salts (BSO1) and test its efficacy as an ethanol sensor, for the first time. BSO was also synthesized using a more well-established coprecipitation method (BSO2), and the influence of the synthesis method on morphology, microstructure and surface chemical composition of BSO was compared using electron microscopy, x-ray diffraction and photoelectron spectroscopy. Both BSO1 and BSO2 exhibited their best responses to 100 ppm of ethanol at 260 °C, but BSO1 showed higher response (12.5) and lower detection limit (0.5 ppm) compared to those of BSO2 (8.2 and 1 ppm) suggesting its superior ethanol sensing properties. The improved sensing of BSO1 was correlated with the corresponding surface morphology and chemical composition.

Electronic properties of p-type BaSnO3 thin films

Cubic perovskite oxides are attracting wide attention for applications in electronics and optoelectronics due to their high electronic mobility, however, realization of p-type conductivity in these oxides is still a matter. Barium stannate (BaSnO3) is one of such materials, wherein low-amount of lanthanum-doping can induce an extremely high room-temperature electron mobility. In this work, anion-doping strategy was explored to realize the p-type conductivity in BaSnO3, and the underlying physics of transport was investigated. It is found that nitrogen substitution for oxygen can induce the p-type conductivity in BaSnO3 thin films. By analyzing the temperature-dependent resistance and negative magnetoresistance data, Efros-Shklovskii variable-range hopping conduction is identified as the dominant transport mechanism in p-type BaSnO3 thin films. Additionally, nitrogen-doped BaSnO3 homojunctions exhibit good rectifying and photo-response properties. This study provides an alternative strategy for realizing the p-type conductivity in stannate-based perovskite oxides, and is helpful for designing the properties of stannate-based devices.

Interfacial charge and strain effects on lanthanum doped barium stannate thin film under ferroelectric gating

Interfacial charge and strain are two coupling effects in semiconductor/ferroelectric epitaxial heterostructures, which are pivotal for use in tailoring functionalities in devices. In this work, La0.04Ba0.96SnO3/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 heterostructures with varying film thicknesses were prepared in order to understand both charge and strain's contributions to the electric-field induced resistance change. The relative resistance change to the lattice strain remains almost unchanged in those thicker films, while increases a little bit in those thinner films. This slight increase is related to the substrate constraint near the interface and follows Freund's strain relaxation model during the dynamic strain induced by the piezoelectric switch. A depletion layer model was also established to simulate the electroresistance variation from the interfacial charge effect. The depletion layer involves an equilibrium between capture and release of electrons by the acceptor-like defects near the interface region. The resistance change vs electric field evolves from a butterfly-like shape to a square-like when decreasing the film thickness, due to the joint effect of strain and interfacial polarization screening charge. This study provides an insight into understanding heteroepitaxial coupling and exploring their potential applications in oxide electronic devices.

Origins of infrared transparency in highly conductive perovskite stannate BaSnO3

Near-infrared absorption in transparent conducting oxides (TCOs) is usually caused by electronic intraband transition at high doping levels. Improved infrared transparency is commonly explained by enhanced drift mobility in these TCOs. Here, an alternative cause behind the high infrared transparency of La-doped barium stannate (LBSO) transparent electrodes is presented. Following the Drude model formalism, we reconstructed spectrally resolved dielectric permittivity for a set of thin films with different free electron concentrations. A comparison of optical properties of LBSO with the tin-doped indium oxide thin films with identical carrier concentrations suggests that the redshift of the screened plasma wavelength for LBSO originates from its large high-frequency dielectric constant of 4.4, one of the highest reported for the s-orbital-based TCOs. Moreover, our measurements confirm an optical mobility significantly higher (>300 cm2/V s) than the drift mobility, effectively suppressing the free carrier absorption. These factors enable high infrared transparency of LBSO films and motivate further exploration of LBSO as broadband TCOs for solar cells and nanophotonics.

Effect of structural design on the electrical, optical and mechanical properties of flexible BaSnO3–Ag composite thin films

Barium stannate (BaSnO3, BS) and silver composite thin films are deposited on flexible polyethylene terephthalate (PET) substrates by magnetron sputtering. The effects of structural design on electrical and optical properties of the BS/Ag/BS tri-layer flexible thin films are investigated systematically. The BS layers can enhance the transmittance significantly, due to the fact that reflection of light from the Ag layer and PET substrate can be suppressed by BS layers. The tri-layer thin films show the high figure of merit of 16.66 × 10−3 Ω−1 and the large commutation quality factor of 197, while the average optical transmittance in the visible light range is above 84% and the sheet resistance is 10.52 Ω/sq. In addition, the flexible tri-layer thin films show outstanding mechanical flexibility, adhesion to PET substrate and stability at high temperature.

2×2R45∘ surface reconstruction and electronic structure of BaSnO3 film

We studied surface and electronic structures of barium stannate (BaSnO$_3$) thin-film by low energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES) techniques. BaSnO$_3$/Ba$_{0.96}$La$_{0.04}$SnO$_3$/SrTiO$_3$ (10 nm/100 nm/0.5 mm) samples were grown using pulsed-laser deposition (PLD) method and were \emph{ex-situ} transferred from PLD chamber to ultra-high vacuum (UHV) chambers for annealing, LEED and ARPES studies. UHV annealing starting from 300$^{\circ}$C up to 550$^{\circ}$C, followed by LEED and ARPES measurements show 1$\times$1 surfaces with non-dispersive energy-momentum bands. The 1$\times$1 surface reconstructs into a $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ one at the annealing temperature of 700$^{\circ}$C where the ARPES data shows clear dispersive bands with valence band maximum located around 3.3 eV below Fermi level. While the $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction is stable under further UHV annealing, it is reversed to 1$\times$1 surface by annealing the sample in 400 mTorr oxygen at 600$^{\circ}$C. Another UHV annealing at 600$^{\circ}$C followed by LEED and ARPES measurements, suggests that LEED $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of electronic structure of BaSnO$_3$ surface and are suggestive of role of oxygen vacancies in the reversible $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction.

A clean approach of biodiesel production from waste cooking oil by using single phase BaSnO3 as solid base catalyst: Mechanism, kinetics & E-study

The current policies of govt. of India on biodiesel production and commercialization have encouraged to explore this area widely. In this study barium stannate perovskite was synthesized to evaluate its activity and stability as a solid base catalyst in biodiesel synthesis from waste cooking oil (WCO). Physicochemical characterizations of the catalyst and feedstock were thoroughly investigated by various techniques. Experimental planning was executed to investigate the impact of various parameters on methyl esterification reaction. 98% fatty acid methyl ester (FAME) conversion was achieved at following optimum reaction condition: Ba: Sn atomic ratio 1:1, catalyst activation temperature 850 °C, oil to methanol molar ratio 1 : 16, catalyst concentration 2.5 wt%, temperature 65°C, time 25 min. Catalyst endurance test suggested that the BaSnO3 has the appreciable catalyzing potency and stability for several times use. The characteristic difference in FTIR of fresh catalyst and used catalyst indicated the mode of interaction between catalyst and reactants. On this basis a plausible E-R mechanism has been proposed. Kinetic study of the transesterification process by using BaSnO3 revealed that this process was base catalyzed transesterification and followed non spontaneous endothermic pathway. High turnover frequency and low E-factor of the catalyst implied that biodiesel production from waste cooking oil by using BaSnO3 was fast, efficient and benign to all environmental prospective.

Hydration of acceptor-doped BaSnO3: Implications of the bound states of ionic defects

The implications of acceptor-bound ionic defects in the hydration of acceptor-doped cubic perovskite BaSnO3 are elucidated based on the thermogravimetric analysis of water uptake and the authors’ recent statistical theory. The oxides BaSn1–xScxO3–δ (0.10 ≤ x ≤ 0.37) and BaSn0.9Sc0.1–xInxO3–δ (x = 0.05, 0.10) were synthesized and experimentally studied. The thermogravimetric measurements showed very good hydration properties of BaSn1–xScxO3–δ: the low-temperature hydrogen concentration was close to the nominal dopant content for all doping levels. The obtained data pertaining to the dopant concentration effect on the hydration isobars are well described by the exploited theory that accounts for the trapping of protons and oxygen vacancies by acceptors. The experimental findings on the effect of scandium substitution with indium on the hydrogen dissolution in the BaSn0.9Sc0.1–xInxO3–δ oxides are also in good agreement with our theoretical predictions. In addition, we discuss the impact of trapping on the hydration enthalpy, entropy and Gibbs free energy of BaSnO3 doped with various acceptors, and establish the type and concentration of acceptor impurities which enhance or inhibit hydration. Our results testify to the pivotal role of the defects’ trapping by acceptors in the hydration of barium stannate, and demonstrate that this effect is important for understanding and prediction of the hydration properties of acceptor-doped perovskites.

Dense Y-doped ion conducting perovskite films of BaZrO3, BaSnO3, and BaCeO3 for SOFC applications produced by powder aerosol deposition at room temperature

State-of-the-art solid oxide fuel cells (SOFC) are based on oxide ion conducting zirconia electrolytes, typically doped by yttria or scandia. Major drawback of these systems are their high operation temperatures of 800 °C and above. These are necessary for a sufficient ionic conductivity. Instead of oxide ions, also protonic charge carriers could be used in SOFC. The material classes of barium zirconates (BaZrO3), barium stannates (BaSnO3), and barium cerates (BaCeO3) are described as good proton conductors, especially when the B-site of the ABO3 perovskite structure is aliovalently doped by yttria. Their protonic conductivity values in the moderate temperature regime up to 600 °C are comparable to YSZ at 800 °C, making these compounds ideal candidates for a usage in future SOFC. Unfortunately, very high sintering temperatures up to 1800 °C are required to process dense and therefore gas-tight solid electrolyte membranes. However, a novel spray coating method called powder aerosol deposition (PAD, also known as AD) enables to form fully dense ceramic films directly at room temperature without any necessary sintering processes. Films are deposited from ceramic powders that are accelerated by a dry carrier gas flow under vacuum conditions.In this work, we investigated the film formation of three different barium based perovskite ceramics, namely yttria doped barium zirconate, barium stannate, and barium cerate by powder aerosol deposition. The optical and mechanical quality of films was evaluated using scanning electron microscopy and microhardness indentation and their crystallographic properties were characterized by X-ray diffraction. The electrical behavior was analyzed by electrochemical impedance spectroscopy and DC polarization methods up to temperatures of 1000 °C and 800 °C, respectively. Furthermore, a preliminary study about the film formation on porous electrodes was conducted.

Induced ferromagnetism and enhanced optical behaviour in indium-doped barium stannate system

Structural, morphological, optical and magnetic properties of chemically synthesized Indium-doped BaSnO3 (BSO) nanostructures were investigated. XRD results indicated cubic structure from Rietveld refinements and FT-IR studies confirmed the characteristic vibrations for all doped compounds. The presence of oxygen vacancies were derived from the defect-induced Raman modes. Surface morphological studies by HR-SEM showed a significant change from pseudo-cuboids to mixed rods. The presence of oxygen vacancies, oxidation states and elements (Ba, Sn, O and In) were studied by X-ray Photoelectron spectroscopy. UV–Vis and Photoluminescence studies demonstrated a decreasing tendency in bandgap values and the presence of defect states. Interesting defect sites and F-centres were probed by Electron paramagnetic resonance studies. A transition from diamagnetic to ferromagnetic behaviour observed from room temperature magnetic measurements was explained based on F-centre exchange interaction.

Dielectric Phase Transition Behaviour Study of Dry Route Derived (BA0.5 SN0.5) TIO3 Ceramics

Ceramic materials display a wide range of properties that facilitate their use in many different product areas. Currently, there has been keen interest in the field of ceramic materials due to their excellent mechanical and physical properties. Barium Stannate Titanate (BST) is a binary solid solution system composed of ferroelectric Barium titanate and non-ferroelectric barium titanate. In this study, the phase transition behavior of (Ba1-xSnx)TiO3 (x = 0.5) (BST) ceramics was obtained by the dry-route method. The previous studies were based on Sn 2+ on the Ti site with varying values of x. The powders after calcination are compacted in the form of pellets using a hydraulic press at an optimized load above 70KN. The experimental density of our sample measured by liquid displacement method with glycerin was lower than theoretical density, giving the shape is highly dense with low porosity. The structure shows that on increasing the Sn2+ content volume decreases due to the size of Sn2+, which is smaller than that of Ba2+, in comparison to BaTiO3. As the demand of lead-free environment-friendly sensor is increasing, thus obtained BST has great applications as a sensor material in modern electronic devices.

Jonscher indices for dielectric materials

Two parameters are proposed as Jonscher indices, named after A. K. Jonscher for his pioneering contribution to the universal dielectric relaxation law. Time domain universal dielectric relaxation law is then obtained from the asymptotic behavior of dielectric response function and relaxation function by replacing parameters in Mittag–Leffler functions with Jonscher indices. Relaxation types can be easily determined from experimental data of discharge current in barium stannate titanate after their Jonscher indices are determined.

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol.

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100W and 50Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α=0.5), the rate constant for electron transfer (ks=1.16s-1) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50μM. The lowest detection limit (LoD) was calculated to be 1μM and sensitivity of 0.81 μA μM-1 cm-2. A 100-fold excess of various ions, such as Ca2+, Na+, K+, Cl-, I-, CO32-, NO3, NH4+ and SO42- did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.

Oxygen deficiency induced strong electron localization in lanthanum doped transparent perovskite oxide BaSnO3

In this paper, we prepare heavily electron doped $\mathrm{L}{\mathrm{a}}_{0.04}\mathrm{B}{\mathrm{a}}_{0.96}\mathrm{Sn}{\mathrm{O}}_{3}$ (LBSO) thin films on a $\mathrm{SrTi}{\mathrm{O}}_{3}$ (STO) substrate by the pulsed laser deposition method under different oxygen pressures, in which different levels of oxygen vacancy concentrations are present. Normally, oxygen vacancies are implicitly assumed as isolated point defects that dope the materials with electron carriers, whereas oxygen-deficient LBSO films exhibit an apparent metal-to-insulator transition combined with lower carrier concentrations and mobility with increased oxygen vacancies, which are concluded from the transport measurement data. Considering the almost constant density of threading dislocations and the higher formation energies for other intrinsic crystal defects, the observed transport trends are ascribed to the extra oxygen vacancies introduced. Therefore, strong electron localization originating from the interaction between the oxygen vacancy and La impurity is proposed for interpreting the behavior in oxygen-deficient LBSO films. Oxygen-deficient crystal structure models for LBSO have been optimized and the electronic structures are revealed by first-principles calculations based on the density functional theory. The partial density of states results indicate that strong electron localization comes from the deep strongly localized states in the forbidden gap, which are mainly composed of hybridized orbitals of $\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$ with $\mathrm{Sn}\phantom{\rule{0.16em}{0ex}}5s5p$ and some amount of $\mathrm{Sn}\phantom{\rule{0.16em}{0ex}}4d$. Thus, the control of the oxygen defects and the related electronic states in barium stannate is essential for achieving optimal electrical performance and as potential applications in perovskite heterostructure devices.

Metalorganic chemical vapor deposition and investigation of nonstoichiometry of undoped BaSnO3 and La-doped BaSnO3 thin films

Wide bandgap (~3 eV) perovskite transparent conductive oxide material exhibiting superior electric properties is highly desired in today's optoelectronics. Just recently La-doped barium stannate (LBSO) bulk n-type semiconductor with outstanding carrier mobility (~320 cm2 V−1 s−1) at high carrier density (1020 cm−3) has been discovered. Highly conductive thin LBSO film synthesis has been challenging due to large lattice mismatch and nonstoichiometry as being the least investigated. Therefore, in this work, the Pulsed injection metalorganic chemical vapor deposition method was used for the growth of undoped BaSnO3 (BSO) and La-doped BaSnO3 thin films. Film depositions were carried out on monocrystalline LaAlO3, SrTiO3, Al2O3 substrates in wide stoichiometric range. Deviation from stoichiometric composition in BSO (Sn/Ba) and LBSO (Sn/(Ba + La)) had a significant impact on microstructure, optical, and electric properties while maintaining cubic symmetry. Near-stoichiometric films even grown at a high rate of ~10 nm/min showed sufficient electric properties.

Influence of Gd+3 incorporation on ethanol sensing properties of Barium Stannate microrod films prepared by coprecipitation method

Ethanol sensing is an important area of research given its relevance to human health, traffic control and various industries. Metal oxide semiconductor nanostructures are most commonly used as gas sensors. In this study, enhanced ethanol sensing properties were obtained by incorporation of Gd3+ ions into Barium Stannate (GBSO), a bimetallic oxide microrods prepared through a simple co-precipitation method. The GBSO films, when exposed to ethanol, showed that incorporation of Gd improved the sensing response till 3 wt% of Gd (3GBSO) loading while further increase in Gd content resulted in reduced response. 3GBSO sample showed response as high as 76 to 500 ppm of ethanol vapor at an operating temperature of 220 °C along with a very low detection limit of 0.1 ppm (response of 1.5). Good repeatability and moderate stability were also observed suggesting its potential as low-cost ethanol sensor. Significant increase in both specific surface area as well as oxygen content (as measured by x-ray photoelectron spectroscopy) was observed in 3GBSO sample compared to that of BSO. Thus, we showed that incorporation of Gd improved the surface area of BSO microrods and in turn the surface adsorption of oxygen which led to their enhanced response to ethanol.

Local Structure and Its Impact on Ionic Conductivity in Cubic Perovskite Protonic Conductor, an Ab-Initio Based cluster Expansion Study

Cubic perovskite of ceramics are typical parent structures for proton conducting electrolyte in intermediate-temperature solid oxide fuel cells, e.g. BZCYYb1. Proton conductivity within this type of materials is well known to be affected by hydration capability, as well as proton mobility. Although a few previous experimental characterizations2-5have unveiled a few pieces of information regarding local structures of proton, dopant and vacancy, a systematic and comprehensive understanding of the underline driving-force for local structure evolution is lacking. Similarly, typical ab-initioDFT calculations assume a fixed dopant concentration with very limited configurations in consideration6-12. Atomically, local structure is the fundamental building-block that constitutively determines macroscopic hydration and mobility of ions. By carrying out ab-initiocalculations, with cluster expansion and Monte-Carlo simulations, competition between entropic-driven defect randomization and enthalpic-driven defect agglomeration is discovered. A temperature vs. dopant-concentration phase diagram is generated. Conductivity is a consequence of dopant, vacancy and proton interactions. Although trapping effects acting on vacancy and proton vary among dopants, a statistical average of ionic mobility is generated through the above approach. By using BaHfO3 as the prototype, representative dopants such as In, K, Sc, Y, Gd, Lu are taken as examples. REFERENCES Yang, L.; Wang, S. Z.; Blinn, K.; Liu, M. F.; Liu, Z.; Cheng, Z.; Liu, M. L., Enhanced Sulfur and Coking Tolerance of a Mixed Ion Conductor for SOFCs: BaZr0.1Ce0.7Y0.2-xYbxO3-delta. Science 2009, 326(5949), 126-129. Mburu, C. W.; Gaita, S. M.; Knee, C. S.; Gatari, M. J.; Karlsson, M., Influence of Yttrium Concentration on Local Structure in BaZr1–xYxO3−δ Based Proton Conductors. The Journal of Physical Chemistry C 2017, 121(30), 16174-16181. Noferini, D.; Koza, M. M.; Rahman, S. M. H.; Evenson, Z.; Nilsen, G. J.; Eriksson, S.; Wildes, A. R.; Karlsson, M., Role of the doping level in localized proton motions in acceptor-doped barium zirconate proton conductors. Phys Chem Chem Phys 2018, 20(20), 13697-13704. Blanc, F.; Sperrin, L.; Lee, D.; Dervisoglu, R.; Yamazaki, Y.; Haile, S. M.; De Paepe, G.; Grey, C. P., Dynamic Nuclear Polarization NMR of Low-gamma Nuclei: Structural Insights into Hydrated Yttrium-Doped BaZrO3. J Phys Chem Lett 2014, 5(14), 2431-6. Giannici, F.; Shirpour, M.; Longo, A.; Martorana, A.; Merkle, R.; Maier, J., Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3. Chemistry of Materials 2011, 23(11), 2994-3002. Hermet, J.; Bottin, F.; Dezanneau, G.; Geneste, G., Thermodynamics of hydration and oxidation in the proton conductor Gd-doped barium cerate from density functional theory calculations. Physical Review B 2012, 85(20). Hermet, J.; Torrent, M.; Bottin, F.; Dezanneau, G.; Geneste, G., Hydrogen diffusion in the protonic conductor BaCe1−xGdxO3−x2from density functional theory. Physical Review B 2013, 87(10). Bévillon, É.; Geneste, G., Hydration properties of BaSn0.875M0.125O3−δ substituted by large dopants (M=In, Y, Gd, and Sm) from first principles. Physical Review B 2008, 77(18). Bévillon, É.; Hermet, J.; Dezanneau, G.; Geneste, G., How dopant size influences the protonic energy landscape in BaSn1−xMxO3−x/2(M = Ga, Sc, In, Y, Gd, La). J. Mater. Chem. A 2014, 2(2), 460-471. Geneste, G.; Amadon, B.; Torrent, M.; Dezanneau, G., DFT+U study of self-trapping, trapping, and mobility of oxygen-type hole polarons in barium stannate. Physical Review B 2017, 96(13). Geneste, G.; Dezanneau, G., Competition between elastic and chemical effects in the doping, defect association, and hydration of barium stannate. Solid State Ionics 2017, 308, 121-132. Geneste, G.; Ottochian, A.; Hermet, J.; Dezanneau, G., Proton transport in barium stannate: classical, semi-classical and quantum regimes. Phys Chem Chem Phys 2015, 17(29), 19104-18.

Enhanced microwave absorption properties of La doping BaSnO3 ceramic powder

The lanthanum doping barium stannate nanoparticles have been fabricated facially via a wet chemical reaction and subsequent annealing process. The thermal decomposition, phase purity, morphology and microstructure are characterized by thermo-gravimetric (TG) and differential scanning calorimetric (DSC), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The microwave absorption properties of Ba1−xLaxSnO3 (x = 0, 0.02, 0.04 and 0.06) nanoparticles are carried out by vector network analyzer (VNA). The results reveal that the Ba1−xLaxSnO3 (x = 0.02, 0.04 and 0.06) nanoparticles exhibited enhancement of microwave absorption performance compared with the pure BaSnO3. For sample with x = 0.02, the minimum reflection loss reaches − 43.78 dB at 13.6 GHz and its effective absorption bandwidth lower than − 10 dB reaches 3.12 GHz. And there are two absorption peaks at 9.36 and 10.64 GHz with the minimum reflection loss is − 30.11 and − 31.30 dB, and the bandwidth of lower than − 10 dB can reach up to 3.12 GHz. It means that BaSnO3 by doping of La ions can be used as an excellent microwave absorption material.

Local Symmetry Reduction in Lanthanum Substituted Barium Stannate Ceramics Densified Using Bi2O3 Sintering Aids

Densified Ba1−xLaxSnO3 (BLSO) ceramics were synthesized at relatively lower sintering temperature by a conventional solid state reaction route. X-ray diffraction (XRD) analysis using the Reitveld refinement technique inferred cubic (space group Pm–3m) average crystalline structure. The effect of La-substitution on variations of lattice parameters could be attributed to two competing factors, viz. ionic radii of the dopant and partial reduction of Sn4+ into Sn2+. XRD data indicate local symmetry reduction from cubic to orthorhombic (Pbnm), evident from the observed splitting in {211}p and {310}p peaks of pseudo cubic structure, as well as corresponding super reflections. The synthesized ceramics were highly porous with percentage densification in the range (60–70)% due to the relatively low sintering temperature used. Densification was improved using 2 wt.% Bi2O3 as a sintering aid, which resulted in highly dense ceramics with relative density ≈ 95%. Sintering temperature reduction of ≈ 300°C was also achieved relative to that required in normal solid state synthesis. This is very important to reduce defects and inhibit uneven grain growth. Microstructure and elemental analysis probed through scanning electron microscopy and energy-dispersive x-ray spectroscopy revealed that Bi replaces lanthanum and that liquid phase sintering is mainly responsible for the high densification using the sintering aid. The structural indicators of symmetry reduction were corroborated by experimentally observed Raman modes in an otherwise symmetry-forbidden cubic phase. The local symmetry reduction is attributed mainly to octahedral tilts corresponding to orthorhombic symmetry.