Synthesis and Properties of the Ba2PrWO6 Double Perovskite.

We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.

Preparation of Confined One-Dimensional Boron Nitride Chains in the 1-D Pores of Siliceous Zeolites under High-Pressure, High-Temperature Conditions.

Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B-N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)x chains per pore in BN/TON and BN/MTW, respectively. These 1-D BN chains potentially have interesting photoluminescence properties in the far ultraviolet region of the electromagnetic spectrum.

Amphoteric Be in GaN: Experimental Evidence for Switching between Substitutional and Interstitial Lattice Sites.

We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice. This behavior is observed through the dominance of Be_{Ga} in the positron annihilation signals in Be-doped GaN, while the emergence of V_{Ga} at high temperatures is a consequence of the Be impurities being driven to interstitial positions. The similarity of this behavior to that found for Na and Li in ZnO suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.

Volume and structural relaxation in compressed sodium borate glass.

The structure and properties of glass can be modified through compression near the glass transition temperature (Tg), and such modified structure and properties can be maintained at ambient temperature and pressure. However, once the compressed glass undergoes annealing near Tg at ambient pressure, the modified structure and properties will relax. The challenging question is how the property relaxation is correlated with both the local and the medium-range structural relaxation. In this paper, we answer this question by studying the volume (density) and structural relaxation of a sodium borate glass that has first been pressure-quenched from its Tg at 1 GPa, and then annealed at ambient pressure under different temperature-time conditions. Using 11B MAS NMR and Raman spectroscopy, we find that the pressure-induced densification of the glass is accompanied by a conversion of six-membered rings into non-ring trigonal boron (BIII) units, i.e. a structural change in medium-range order, and an increase in the fraction of tetrahedral boron (BIV), i.e. a structural change in short-range order. These pressure-induced structural conversions are reversible during ambient pressure annealing near Tg, but exhibit a dependence on the annealing temperature, e.g. the ring/non-ring BIII ratio stabilizes at different values depending on the applied annealing temperature. We find that conversions between structural units cannot account for the pressure-induced densification, and instead we suggest the packing of structural units as the main densification mechanism.

Unique effects of thermal and pressure histories on glass hardness: Structural and topological origin.

The properties of glass are determined not only by temperature, pressure, and composition, but also by their complete thermal and pressure histories. Here, we show that glasses of identical composition produced through thermal annealing and through quenching from elevated pressure can result in samples with identical density and mean interatomic distances, yet different bond angle distributions, medium-range structures, and, thus, macroscopic properties. We demonstrate that hardness is higher when the density increase is obtained through thermal annealing rather than through pressure-quenching. Molecular dynamics simulations reveal that this arises because pressure-quenching has a larger effect on medium-range order, while annealing has a larger effect on short-range structures (sharper bond angle distribution), which ultimately determine hardness according to bond constraint theory. Our work could open a new avenue towards industrially useful glasses that are identical in terms of composition and density, but with differences in thermodynamic, mechanical, and rheological properties due to unique structural characteristics.

Mixed alkaline earth effect in the compressibility of aluminosilicate glasses.

The mixed modifier effect (MME) in oxide glasses manifests itself as a non-additive variation in certain properties when one modifier oxide species is substituted by another one at constant total modifier content. However, the structural and topological origins of the MME are still under debate. This study provides new insights into the MME by investigating the effect of isostatic compression on density and hardness of mixed MgO/CaO sodium aluminosilicate glasses. This is done using a specially designed setup allowing isostatic compression of bulk glass samples up to 1 GPa at elevated temperature. A mixed alkaline earth effect is found in the compressibility and relative change of hardness, viz., a local maximum of density as a function of Mg/Ca ratio appears following compression, whereas a local minimum of hardness in the uncompressed glasses nearly disappears after compression. Moreover, the densification of these glasses is found to occur at temperatures much below the glass transition temperature, indicating that a non-viscous mechanism is at play. This is further supported by the fact that density relaxes in a stretched exponential manner upon subsequent annealing at ambient pressure with an exponent of ∼0.62. This is close to the Phillips value of 3/5 for relaxation in three dimensions when both short- and long-range interactions are activated.

Evolution of the Growth Mode and Its Consequences during Bulk Crystallization of GaN.

A detailed analysis of morphology of gallium nitride crystal growth obtained by ammonothermal and halide vapor phase epitaxy methods was carried out. The work was conducted to determine the source of triangular planar defects visible in X-ray topography as areas with locally different lattice parameters. It is shown that the occurrence of these defects is related to growth hillocks. Particular attention was paid to analyzing the manner and consequences of merging hillocks. In the course of the study, the nature of the mentioned defects and the cause of their formation were determined. It was established that the appearance of the defects depends on the angle formed between the steps located on the sides of two adjacent hillocks. A universal growth model is presented to explain the cause of heterogeneity during the merging of growth hillocks.

Correction to "Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions".

[This corrects the article DOI: 10.1021/acsomega.2c00669.].

Comparison of Cattle Housing Systems Based on the Criterion of Damage to Barn Equipment and Construction Errors.

Dairy cattle housing systems are the subject of numerous studies, in which a strong emphasis is placed on the comparison of animal welfare, animal behavior, production indicators and labor inputs. Dairy cattle housing systems are linked to specific livestock buildings, which is a prerequisite for undertaking studies comparing barns and their technical equipment. The aim of the study was to compare barns with two types of housing systems, i.e., tie-stall and freestall, including the identification of technical wear in various areas used by animals. This objective was linked to the assessment of animal health problems in livestock facilities. The research covered 38 dairy farms, 19 of which kept cows in the tie-stall system and 19 in the freestall system. The barns in these farms were examined for technical damage and construction errors, assessed in four areas: lying, feeding, milking and social. The research results confirmed significant differences in the degree of damage to technical equipment in individual areas of barns and between barns with tie-stall and freestall housing systems. The conclusions indicate the need to link the degradation of barns and their technical equipment, as well as design errors with the evaluation of dairy cattle welfare in future studies.

Fundamental Studies on Crystallization and Reaching the Equilibrium Shape in Basic Ammonothermal Method: Growth on a Native Lenticular Seed.

In this paper, a detailed investigation of the basic ammonothermal growth process of GaN is presented. By analyzing the crystallization on a native seed with a lenticular shape, thus with an intentionally varying off-cut, we wanted to answer some basic questions: (i) Which crystallographic planes play the most important role during growth (which planes are formed and which disappear)? (ii) What is the relationship between the growth rates in different crystallographic directions? (iii) What is the influence of the off-cut of the seed on the growth process? Two non-polar slices, namely, 12¯10 and 1¯100, as well as a 0001 basal plane slice of an ammonothermal crystal were analyzed. The examined planes were selectively etched in order to reveal the characteristic features of the growth process. The applied characterization methods included: optical microscopy with Nomarski contrast and ultraviolet illumination, X-ray topography and high-resolution X-ray diffraction, and secondary ion mass spectrometry. The obtained results allowed for creating a growth model of an ammonothermal GaN crystal on a lenticular seed. These findings are of great importance for the general understanding of the basic ammonothermal crystal growth process of GaN.

Pressure Evolution of Glass Transition Temperature in LiFePO4.

LiFePO4 is an important base material for generation of new batteries. One of the important developments is its use in the form of a solid glass, which allows an increase in the electrical conductivity after the high-pressure process. Such a treatment allows full control of the vitrification and nanocrystallization processes as well. This report shows the basic reference for the pressure dependence of the glass transition temperature. The unique behavior has been proven with a maximum of Tg (P) already at moderate pressures. The protocol for depicting the resulting evolution is as follows: it enables a reliable extrapolation beyond the experimental domain. The importance of the presented results for the general topic of glass transition physics is also remarkable due to the scant evidence of the existence of systems with clearly inverted vitrification under compression.

Novel High-Pressure Nanocomposites for Cathode Materials in Sodium Batteries.

A new nanocomposite material was prepared by high pressure processing of starting glass of nominal composition NaFePO4. Thermal, structural, electrical and dielectric properties of the prepared samples were studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and broadband dielectric spectroscopy (BDS). It was demonstrated that high-pressure-high-temperature treatment (HPHT) led to an increase in the electrical conductivity of the initial glasses by two orders of magnitude. It was also shown that the observed effect was stronger than for the lithium analogue of this material studied by us earlier. The observed enhancement of conductivity was explained by Mott's theory of electron hopping, which is more frequent in samples after pressure treatment. The final composite consisted of nanocrystalline NASICON (sodium (Na) Super Ionic CONductor) and alluaudite phases, which are electrochemically active in potential cathode materials for Na batteries. Average dimensions of crystallites estimated from XRD studies were between 40 and 90 nm, depending on the phase. Some new aspects of local dielectric relaxations in studied materials were also discussed. It was shown that a combination of high pressures and BDS method is a powerful method to study relaxation processes and molecular movements in solids. It was also pointed out that high-pressure cathode materials may exhibit higher volumetric capacities compared with commercially used cathodes with carbon additions.

Carbon and Manganese in Semi-Insulating Bulk GaN Crystals.

Co-doping with manganese and carbon was performed in gallium nitride grown by halide vapor phase epitaxy method. Native seeds of high structural quality were used. The crystallized material was examined in terms of its structural, optical, and electrical properties. For that purpose, different characterization methods: x-ray diffraction, Raman spectroscopy, low-temperature photoluminescence, and temperature-dependent Hall effect measurements, were applied. The physical properties of the co-doped samples were compared with the properties of crystals grown in the same reactor, on similar seeds, but doped only with manganese or carbon. A comparison of the electrical and optical properties allowed to determine the role of manganese and carbon in doped and co-doped gallium nitride crystals.

Negative Magnetoresistivity in Highly Doped n-Type GaN.

This paper presents low-temperature measurements of magnetoresistivity in heavily doped n-type GaN grown by basic GaN growth technologies: molecular beam epitaxy, metal-organic vapor phase epitaxy, halide vapor phase epitaxy and ammonothermal. Additionally, GaN crystallized by High Nitrogen Pressure Solution method was also examined. It was found that all the samples under study exhibited negative magnetoresistivity at a low temperature (10 K < T < 50 K) and for some samples this effect was observed up to 100 K. This negative magnetoresistivity effect is analyzed in the frame of the weak localization phenomena in the case of three-dimensional electron gas in a highly doped semiconductor. This analysis allows for determining the phasing coherence time τφ for heavily doped n-type GaN. The obtained τφ value is proportional to T−1.34, indicating that the electron−electron interaction is the main dephasing mechanism for the free carriers.

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions.

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A2BB'X6 group of compounds contains mainly divalent alkali cations in the form of XIIA = Ba2+, Ca2+ sharing, here, oxygen-arranged clusters (IIX = O2-) with purposely selected central ions from f-block VIB = Ce4/3+ and d-block VIB' = W4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Large-Scale Defect Clusters with Hexagonal Honeycomb-like Arrangement in Ammonothermal GaN Crystals.

In this paper, we investigate, using X-ray Bragg diffraction imaging and defect selective etching, a new type of extended defect that occurs in ammonothermally grown gallium nitride (GaN) single crystals. This hexagonal "honeycomb" shaped defect is composed of bundles of parallel threading edge dislocations located in the corners of the hexagon. The observed size of the honeycomb ranges from 0.05 mm to 2 mm and is clearly correlated with the number of dislocations located in each of the hexagon's corners: typically ~5 to 200, respectively. These dislocations are either grouped in areas that exhibit "diameters" of 100-250 µm, or they show up as straight long chain alignments of the same size that behave like limited subgrain boundaries. The lattice distortions associated with these hexagonally arranged dislocation bundles are extensively measured on one of these honeycombs using rocking curve imaging, and the ensemble of the results is discussed with the aim of providing clues about the origin of these "honeycombs".

Structural Analysis of Low Defect Ammonothermally Grown GaN Wafers by Borrmann Effect X-ray Topography.

X-ray topography defect analysis of entire 1.8-inch GaN substrates, using the Borrmann effect, is presented in this paper. The GaN wafers were grown by the ammonothermal method. Borrmann effect topography of anomalous transmission could be applied due to the low defect density of the substrates. It was possible to trace the process and growth history of the GaN crystals in detail from their defect pattern imaged. Microscopic defects such as threading dislocations, but also macroscopic defects, for example dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls and dislocation bundles, were detected. Influences of seed crystal preparation and process parameters of crystal growth on the formation of the defects are discussed.

Vibrational disorder and densification-induced homogenization of local elasticity in silicate glasses.

We report the effect of structural compaction on the statistics of elastic disorder in a silicate glass, using heterogeneous elasticity theory with the coherent potential approximation (HET-CPA) and a log-normal distribution of the spatial fluctuations of the shear modulus. The object of our study, a soda lime magnesia silicate glass, is compacted by hot-compression up to 2 GPa (corresponding to a permanent densification of ~ 5%). Using THz vibrational spectroscopic data and bulk mechanical properties as inputs, HET-CPA evaluates the degree of disorder in terms of the length-scale of elastic fluctuations and the non-affine part of the shear modulus. Permanent densification decreases the extent of non-affine elasticity, resulting in a more homogeneous distribution of strain energy, while also decreasing the correlation length of elastic heterogeneity. Complementary 29Si magic angle spinning NMR spectroscopic data provide a short-range rationale for the effect of compression on glass structure in terms of a narrowing of the Si-O-Si bond-angle and the Si-Si distance.

Indentation Response of Calcium Aluminoborosilicate Glasses Subjected to Humid Aging and Hot Compression.

Aluminoborosilicate glasses find a wide range of applications, which require good mechanical reliability such as surface damage resistance. Calcium aluminoborosilicate (CABS) glasses have recently been found to exhibit so-called intermediate behavior in terms of their response to sharp contact loading. That is, these glasses deform with less shear than normal glass and less densification than anomalous glasses. This deformation mechanism is believed to give rise to high crack initiation resistance of certain CABS glasses. In order to further improve and understand the micromechanical properties of this glass family, we studied the indentation response of different CABS glasses subjected to two types of post-treatment, namely hot compression and humid aging. Upon hot compression, density, elastic moduli, and hardness increased. Specifically, elastic modulus increased by as much as 20% relative to the as-made sample, while the largest change in hardness was 1.8 GPa compared to the as-made sample after hot compression. The pressure-induced increase in these properties can be ascribed to the increase in network connectivity and bond density. On the other hand, the crack initiation resistance decreased, as the hot compression increased the residual stress driving the indentation cracking. Humid aging had only a minor impact on density, modulus, and hardness, but an observed decrease in crack initiation resistance. We discuss the correlations between hardness, density, crack resistance, and deformation mechanism and our study thus provides guidelines for tailoring the mechanical properties of oxide glasses.

Bond Switching in Densified Oxide Glass Enables Record-High Fracture Toughness.

Humans primarily interact with information technology through glass touch screens, and the world would indeed be unrecognizable without glass. However, the low toughness of oxide glasses continues to be their Achilles heel, limiting both future applications and the possibility to make thinner, more environmentally friendly glasses. Here, we show that with proper control of plasticity mechanisms, record-high values of fracture toughness for transparent bulk oxide glasses can be achieved. Through proper combination of gas-mediated permanent densification and rational composition design, we increase the glasses' propensity for plastic deformation. Specifically, we demonstrate a fracture toughness of an aluminoborate glass (1.4 MPa m0.5) that is twice as high as that of commercial glasses for mobile devices. Atomistic simulations reveal that the densification of the adaptive aluminoborate network increases coordination number changes and bond swapping, ultimately enhancing plasticity and toughness upon fracture. Our findings thus provide general insights into the intrinsic toughening mechanisms of oxide glasses.