Crystal Structure, Cation Occupation, and Phase Transitions in Ba(LiNa)NbO Tetragonal Tungsten Bronzes.

The chemical flexibility of the tetragonal tungsten bronze (TTB) structure offers a large potential for compositional engineering. Cation size and vacancy concentration are known to affect its structure, cation disorder, and functional properties. However, the compositional complexity also makes the TTB structure challenging to understand.

The effect of cation size on structure and properties of Ba-based tetragonal tungsten bronzes BaMNbO (M = Na, K or Rb) and BaMNbTiO (M = Ca or Sr).

The second largest family of oxide ferroelectrics, after perovskites, are the tetragonal tungsten bronzes (TTB) with the general formula A2A1CB1B2O. Cation disorder in TTBs is known to occur if the size difference between cations is small, but the impact of cation disorder on structure and properties has not yet been extensively addressed. In this study we investigate the effect of the size of the M cation, including cation disorder, on the crystal structure and dielectric properties in the two series BaMNbO (BMN, A = Na, K and Rb) and BaMNbTiO (BMNT, M = Ca, Sr).

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic structure of a pristine monolayer of h-BN is dependent on the type of substrate, as h-BN is decoupled electronically from the HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111) substrate, metallic-like behavior is predicted.

Theoretical and Experimental Determination of Thermomechanical Properties of Epoxy-SiO Nanocomposites.

Improvements in the thermomechanical properties of epoxy upon inclusion of well-dispersed SiO nanoparticles have been demonstrated both experimentally and through molecular dynamics simulations. The SiO was represented by two different dispersion models: dispersed individual molecules and as spherical nanoparticles. The calculated thermodynamic and thermomechanical properties were consistent with experimental results.

Cation Disorder in Ferroelectric BaMNbO (M = Na, K, and Rb) Tetragonal Tungsten Bronzes.

The crystal structure of tetragonal tungsten bronzes, with the general formula A1A2CB1B2O, is flexible both from a chemical and structural viewpoint, resulting in a multitude of compositions. The A1 and A2 lattice sites, with different coordination environments, are usually regarded to be occupied by two different cations such as in BaNaNbO with Na and Ba occupying the A1 and A2 sites, respectively. Here, we report on a systematic study of the lattice site occupancy on the A1 and A2 sites in the series BaMNbO (M = Na, K, and Rb).

Modulating acrylic acid content of nanogels for drug delivery & biocompatibility studies.

Dual stimuli-responsive nanogels (NGs) have gained popularity in the field of bio medicine due to their versatile nature of applicability. Poly(N-isopropylacrylamide)-co-poly(acrylic acid) (pNIPAm-pAAc)-based NGs provide such dual stimuli-response with pNIPAm and pAAc providing thermal and pH-based responses, respectively. Studying the growth of these NGs, as well as, understanding the effect of the incorporation of pAAc in the NG matrix, is important in determining the physico-chemical properties of the NG.

Hydrothermal synthesis of hexagonal YMnO and YbMnO below 250 °C.

The hydrothermal synthesis of hexagonal YMnO3 and YbMnO3 are reported using high KOH mineraliser concentrations (>10 M) and low temperatures (<240 °C). The relation between reaction parameters and resulting phase purity were mapped by ex situ and in situ X-ray diffraction. Excess Y2O3 resulted in two-phase product with hexagonal YMnO3 with different lattice parameters.

The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO.

Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO nanocomposites was employed, where surface-functionalized SiO (up to 5 wt.%) is synthesized directly in the epoxy.

Structures and Role of the Intermediate Phases on the Crystallization of BaTiO from an Aqueous Synthesis Route.

Carbonate formation is a prevailing challenge in synthesis of BaTiO, especially through wet chemical synthesis routes. In this work, we report the phase evolution during thermal annealing of an aqueous BaTiO precursor solution, with a particular focus on the structures and role of intermediate phases forming prior to BaTiO nucleation. infrared spectroscopy, X-ray total scattering, and transmission electron microscopy were used to reveal the decomposition, pyrolysis, and crystallization reactions occurring during thermal processing.

Understanding the Hydrothermal Formation of NaNbO: Its Full Reaction Scheme and Kinetics.

Sodium niobate (NaNbO) attracts attention for its great potential in a variety of applications, for instance, due to its unique optical properties. Still, optimization of its synthetic procedures is hard due to the lack of understanding of the formation mechanism under hydrothermal conditions. Through X-ray diffraction, hydrothermal synthesis of NaNbO was observed in real time, enabling the investigation of the reaction kinetics and mechanisms with respect to temperature and NaOH concentration and the resulting effect on the product crystallite size and structure.

Fluorescent Nanocomposites: Hollow Silica Microspheres with Embedded Carbon Dots.

Intrinsically fluorescent carbon dots may form the basis for a safer and more accurate sensor technology for digital counting in bioanalytical assays. This work presents a simple and inexpensive synthesis method for producing fluorescent carbon dots embedded in hollow silica particles. Hydrothermal treatment at low temperature (160 °C) of microporous silica particles in presence of urea and citric acid results in fluorescent, microporous and hollow nanocomposites with a surface area of 12 m /g.

Time-Enhanced Performance of Oxide Thermoelectric Modules Based on a Hybrid p-n Junction.

The present challenge with all-oxide thermoelectric modules is their poor durability at high temperatures caused by the instability of the metal-oxide interfaces at the hot side. This work explains a new module concept based on a hybrid p-n junction, fabricated in one step by spark plasma co-sintering of CaCo O (CCO, p-type) and CaMnO/CaMnO (CMO, n-type). Different module (unicouple) designs were studied to obtain a thorough understanding of the role of the formed hybrid p-n junction of CaCoMnO (CCMO, p-type) and Co-oxide rich phases (p-type) at the p-n junction (>700 °C) in the module performance.

Biocompatibility of Piezoelectric KNaNbO Thin Films on Platinized Silicon Substrates.

Lead-free piezoelectric ceramics like KNaNbO (KNN) represent an emerging class of biomaterials for medical technology, as they can be used as components in implantable microelectromechanical systems (MEMS) and bioactive scaffolds for tissue stimulation. Such functional materials can act as working components in future devices, and their addition to current implant designs can greatly improve the biological interaction between host and implant. Despite this, only a few reports have studied the biocompatibility of these materials with living cells.

Memristive TiO: Synthesis, Technologies, and Applications.

Titanium dioxide (TiO) is one of the most widely used materials in resistive switching applications, including random-access memory, neuromorphic computing, biohybrid interfaces, and sensors. Most of these applications are still at an early stage of development and have technological challenges and a lack of fundamental comprehension. Furthermore, the functional memristive properties of TiO thin films are heavily dependent on their processing methods, including the synthesis, fabrication, and post-fabrication treatment.

Experimental setup for high-temperature in situ studies of crystallization of thin films with atmosphere control.

Understanding the crystallization process for chemical solution deposition (CSD) processed thin films is key in designing the fabrication strategy for obtaining high-quality devices. Here, an in situ sample environment is presented for studying the crystallization of CSD processed thin films under typical processing parameters using near-grazing-incidence synchrotron X-ray diffraction. Typically, the pyrolysis is performed in a rapid thermal processing (RTP) unit, where high heating rates, high temperatures and atmosphere control are the main control parameters.

A Fast, Low-Temperature Synthesis Method for Hexagonal YMnO : Kinetics, Purity, Size and Shape as Studied by In Situ X-ray Diffraction.

The reaction mechanisms, phase development and kinetics of the hydrothermal synthesis of hexagonal-YMnO from Y O and Mn O using in situ X-ray diffraction are reported under different reaction conditions with temperatures ranging from 300 to 350 °C, and using 1, 5 and 10 m KOH, and 5 m NaOH mineraliser. Reactions initiated with Y O hydrating to Y(OH) , which then dehydrated to YO(OH). Higher temperatures and KOH concentrations led to faster, more complete dehydrations.

Controlled Growth of Sr Ba Nb O Hopper- and Cube-Shaped Nanostructures by Hydrothermal Synthesis.

Controlling the shape and size of nanostructured materials has been a topic of interest in the field of material science for decades. In this work, the ferroelectric material Sr Ba Nb O (x=0.32-0.

Compositional Engineering of LaBaCoO-(1-) BaZrYO ( = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) Nanocomposite Cathodes for Protonic Ceramic Fuel Cells.

Compositionally engineered LaBaCoO-(1-) BaZrYO ( = 0.6, 0.7, 0.

All-Oxide Thermoelectric Module with in Situ Formed Non-Rectifying Complex p-p-n Junction and Transverse Thermoelectric Effect.

All-oxide thermoelectric modules for energy harvesting are attractive because of high-temperature stability, low cost, and the potential to use nonscarce and nontoxic elements. Thermoelectric modules are mostly fabricated in the conventional π-design, associated with the challenge of unstable metallic interconnects at high temperature. Here, we report on a novel approach for fabrication of a thermoelectric module with an in situ formed p-p-n junction made of state-of-the-art oxides CaCo O (p-type) and CaMnO-CaMnO composite (n-type).

Biocompatibility of (Ba,Ca)(Zr,Ti)O piezoelectric ceramics for bone replacement materials.

Total joint replacement implants are generally designed to physically mimic the biological environment to ensure compatibility with the host tissue. However, implant instability exposes patients to long recovery periods, high risk for revision surgeries, and high expenses. Introducing electrical stimulation to the implant site to accelerate healing is promising, but the cumbersome nature of wired devices is detrimental to the implant design.

Controlling Phase Purity and Texture of KNaNbO Thin Films by Aqueous Chemical Solution Deposition.

Aqueous chemical solution deposition (CSD) of lead-free ferroelectric KNaNbO (KNN) thin films has a great potential for cost-effective and environmentally friendly components in microelectronics. Phase purity of KNN is, however, a persistent challenge due to the volatility of alkali metal oxides, usually countered by using excess alkali metals in the precursor solutions. Here, we report on the development of two different aqueous precursor solutions for CSD of KNN films, and we demonstrate that the decomposition process during thermal processing of the films is of detrimental importance for promoting nucleation of KNN and suppressing the formation of secondary phases.

In Situ Synthesis of Hybrid Inorganic⁻Polymer Nanocomposites.

Hybrid inorganic⁻polymer nanocomposites can be employed in diverse applications due to the potential combination of desired properties from both the organic and inorganic components. The use of novel bottom⁻up in situ synthesis methods for the fabrication of these nanocomposites is advantageous compared to top⁻down ex situ mixing methods, as it offers increased control over the structure and properties of the material. In this review, the focus will be on the application of the sol⁻gel process for the synthesis of inorganic oxide nanoparticles in epoxy and polysiloxane matrices.

Epitaxial KNaNbO thin films by aqueous chemical solution deposition.

We report on an environmentally friendly and versatile aqueous chemical solution deposition route to epitaxial KNaNbO (KNN) thin films. The route is based on the spin coating of an aqueous solution of soluble precursors on SrTiO single crystal substrates followed by pyrolysis at 400°C and annealing at 800°C using rapid thermal processing. Strongly textured films with homogeneous thickness were obtained on three different crystallographic orientations of SrTiO.