Competition between Anion-Deficient Oxide and Oxyhydride Phases during the Topochemical Reduction of LaSrCoRuO.

Binary metal hydrides can act as low-temperature reducing agents for complex oxides in the solid state, facilitating the synthesis of anion-deficient oxide or oxyhydride phases. The reaction of LaSrCoRuO, with CaH in a sealed tube yields the face-centered cubic phase LaSrCoRuOH. The reaction with LiH under similar conditions converts LaSrCoRuO to a mixture of tetragonal LaSrCoRuOH and cubic LaSrCoRuOH.

Disproportionation of Co in the Topochemically Reduced Oxide LaSrCoRuO.

Complex transition-metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition-metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO , using Zr, yields LaSrCoRuO . This reduced phase contains an ordered array of apex-linked square-based pyramidal Ru O , square-planar Co O and octahedral Co O units, consistent with the coordination-geometry driven disproportionation of Co .

Solution-gel-based surface modification of LiNiMnO with amorphous Li-Ti-O coating.

LNMO (LiNiMnO) is a high-energy density positive electrode material for lithium ion batteries. Unfortunately, it suffers from capacity loss and impedance rise during cycling due to electrolyte oxidation and electrode/electrolyte interface instabilities at high operating voltages. Here, a solution-gel synthesis route was used to coat 0.

Anion redox as a means to derive layered manganese oxychalcogenides with exotic intergrowth structures.

Topochemistry enables step-by-step conversions of solid-state materials often leading to metastable structures that retain initial structural motifs. Recent advances in this field revealed many examples where relatively bulky anionic constituents were actively involved in redox reactions during (de)intercalation processes. Such reactions are often accompanied by anion-anion bond formation, which heralds possibilities to design novel structure types disparate from known precursors, in a controlled manner.

Structures and Magnetic Ordering in Layered Cr Oxide Arsenides SrCrOCrOAs and SrCrOCrAs.

Two novel chromium oxide arsenide materials have been synthesized, SrCrOCrOAs (i.e., SrCrAsO) and SrCrOCrAs (i.

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the LiMoO Solid Solutions.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide LiMoO, which has generally been considered as a phase with a well-defined chemical composition. LiMoO (-0.037 ≤ ≤ 0.

The crystal and defect structures of polar KBiNbO.

KBiNbO was prepared from RbBiNbO by a sequence of cation exchange reactions which first convert RbBiNbO to LiBiNbO, before KBiNbO is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNbO adopts a polar, layered, perovskite structure (space group 11) in which the BiNbO layers are stacked in a (0, ½, ) arrangement, with the K cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi cations parallel to the -axis.

The influence of the 6s configuration of Bi on the structures of A'BiNbO (A' = Rb, Na, Li) layered perovskite oxides.

Solid state compounds which exhibit non-centrosymmetric crystal structures are of great interest due to the physical properties they can exhibit. The 'hybrid improper' mechanism - in which two non-polar distortion modes couple to, and stabilize, a further polar distortion mode, yielding an acentric crystal structure - offers opportunities to prepare a range of novel non-centrosymmetric solids, but examples of compounds exhibiting acentric crystal structures stabilized by this mechanism are still relatively rare. Here we describe a series of bismuth-containing layered perovskite oxide phases, RbBiNbO, LiBiNbO and NaBiNbO, which have structural frameworks compatible with hybrid-improper ferroelectricity, but also contain Bi cations which are often observed to stabilize acentric crystal structures due to their 6s electronic configurations.

Topochemical Deintercalation of Li from Layered LiNiB: toward 2D MBene.

The pursuit of two-dimensional (2D) borides, MBenes, has proven to be challenging, not the least because of the lack of a suitable precursor prone to the deintercalation. Here, we studied room-temperature topochemical deintercalation of lithium from the layered polymorphs of the LiNiB compound with a considerable amount of Li stored in between [NiB] layers (33 at. % Li).

Magnetic Ordering in the Layered Cr(II) Oxide Arsenides SrCrOCrAs and BaCrOCrAs.

SrCrOCrAs and BaCrOCrAs with Cr ions in CrO sheets and in CrAs layers crystallize with the SrMnSbO structure (space group 4/, = 2) and lattice parameters = 4.00800(2) Å, = 18.8214(1) Å (SrCrOCrAs) and = 4.

Exsolution of SrO during the Topochemical Conversion of LaSrCoRuO to the Oxyhydride LaSrCoRuOH.

 Reaction of the  = 1 Ruddlesden-Popper oxide LaSrCoRuO with CaH yields the oxyhydride phase LaSrCoRuOH via a topochemical anion exchange. Close inspection of the X-ray and neutron powder diffraction data in combination with HAADF-STEM images reveals that the nanoparticles of SrO are exsolved from the system during the reaction, with the change in cation stoichiometry accommodated by the inclusion of  > 1 (Co/Ru)OH "perovskite" layers into the Ruddlesden-Popper stacking sequence. This novel pseudotopochemical process offers a new route for the formation of > 1 Ruddlesden-Popper structured materials.

Computationally Driven Discovery of a Family of Layered LiNiB Polymorphs.

Two novel lithium nickel boride polymorphs, RT-LiNiB and HT-LiNiB, with layered crystal structures are reported. This family of compounds was theoretically predicted by using the adaptive genetic algorithm (AGA) and subsequently synthesized by a hydride route with LiH as the lithium source. Unique among the known ternary transition-metal borides, the LiNiB structures feature Li layers alternating with nearly planar [NiB] layers composed of Ni hexagonal rings with a B-B pair at the center.

Influence of Mono- and Bimetallic PtO, PdO PtPdO Clusters on CO Sensing by SnO₂ Based Gas Sensors.

To obtain a nanocrystalline SnO₂ matrix and mono- and bimetallic nanocomposites SnO₂/Pd, SnO₂/Pt, and SnO₂/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The electronic state of the metals in mono- and bimetallic clusters was determined using X-ray photoelectron spectroscopy (XPS).

Effects of Ag Additive in Low Temperature CO Detection with In₂O₃ Based Gas Sensors.

Nanocomposites In₂O₃/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25⁻250 °C. Nanocrystalline In₂O₃ and In₂O₃/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H₂) method.

Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp.

The rapid progress in materials science that enables the design of materials down to the nanoscale also demands characterization techniques able to analyze the materials down to the same scale, such as transmission electron microscopy. As Belgium's foremost electron microscopy group, among the largest in the world, EMAT is continuously contributing to the development of TEM techniques, such as high-resolution imaging, diffraction, electron tomography, and spectroscopies, with an emphasis on quantification and reproducibility, as well as employing TEM methodology at the highest level to solve real-world materials science problems. The lab's recent contributions are presented here together with specific case studies in order to highlight the usefulness of TEM to the advancement of materials science.

Synthesis of MAX Phases in the Zr-Ti-Al-C System.

This study reports on the synthesis and characterization of MAX phases in the (Zr,Ti)AlC system. The MAX phases were synthesized by reactive hot pressing and pressureless sintering in the 1350-1700 °C temperature range. The produced ceramics contained large fractions of 211 and 312 (n = 1, 2) MAX phases, while strong evidence of a 413 (n = 3) stacking was found.

Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations.

Objective: The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, YO content and LaO doping on the translucency.

Methods: Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n=6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR).

Synthesis and cation distribution in the new bismuth oxyhalides with the Sillén-Aurivillius intergrowth structures.

About 20 new compounds with the Sillén-Aurivillius intergrowth structure, Me(1)Me(2)Bi3Nb2O11X (Me(1) = Pb, Sr, Ba; Me(2) = Ca, Sr, Ba; X = Cl, Br, I), have been prepared. They are composed of stacking of [ANb2O7] perovskite blocks, fluorite-type [M2O2] blocks and halogen sheets. The cation distribution between the fluorite and perovskite layers has been studied for Ba2Bi3Nb2O11I, Ca1.

Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics.

The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe(III) acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO2.

KCN Chemical Etch for Interface Engineering in Cu2ZnSnSe4 Solar Cells.

The removal of secondary phases from the surface of the kesterite crystals is one of the major challenges to improve the performances of Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. In this contribution, the KCN/KOH chemical etching approach, originally developed for the removal of CuxSe phases in Cu(In,Ga)(S,Se)2 thin films, is applied to CZTSe absorbers exhibiting various chemical compositions. Two distinct electrical behaviors were observed on CZTSe/CdS solar cells after treatment: (i) the improvement of the fill factor (FF) after 30 s of etching for the CZTSe absorbers showing initially a distortion of the electrical characteristic; (ii) the progressive degradation of the FF after long treatment time for all Cu-poor CZTSe solar cell samples.

Synergy between transmission electron microscopy and powder diffraction: application to modulated structures.

The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal X-ray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem.