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High-temperature phase relations in the La2O3–TiO2–Nb2O5 ternary system were investigated at 1290 °C using SEM, EDS and XRD, and a subsolidus phase equilibrium diagram was constructed. It was demonstrated that the addition of the La1/3NbO3 to the La2O3:3TiO2 mixture completely stabilizes a perovskite-La2/3TiO3 compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La2O3:TiO2 =1:3 dissolves in La1/3NbO3 up to 15 mol% TiO2. Moreover, a newly defined composition of compound La30Ti16Nb4O87 formed in the La2O3-rich part of the system and a solid solution La3Ti5Nb10O39.5–La2Ti2Nb8O27 were proposed. In the binary subsystem LaTiNbO6-La0.462Ti0.386Nb0.614O3, the components exhibit opposite temperature dependence of resonant frequency in the microwave frequency range. Thus, the dielectric properties of the prepared ceramics can be tailored by varying the component concentration and thermally stable dielectric properties can be achieved for a composition with a LaTiNbO6/La0.462Ti0.386Nb0.614O3 molar ratio of 0.27.

In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)5Sn3 partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.

Mo$_8$O$_{23}$ is a low-dimensional chemically robust transition metal oxide coming from a prospective family of functional materials, MoO$_{3-x}$, ranging from a wide gap insulator $(x=0)$ to a metal $(x=1)$. The large number of stoichometric compounds with intermediate $x$ have widely different properties. In Mo$_8$O$_{23}$, an unusual charge density wave transition has been suggested to occur above room temperature, but its low temperature behaviour is particularly enigmatic. We present a comprehensive experimental study of the electronic structure associated with various ordering phenomena in this compound, complemented by theory. Density-functional theory (DFT) calculations reveal a cross-over from a semi-metal with vanishing band overlap to narrow-gap semiconductor behaviour with decreasing temperature. A buried Dirac crossing at the zone boundary is confirmed by angle-resolved photoemission spectroscopy (ARPES). Tunnelling spectroscopy (STS) reveals a gradual gap opening corresponding to a metal-to-insulator transition at 343 K in resistivity, consistent with CDW formation and DFT results, but with large non-thermal smearing of the spectra implying strong carrier scattering. At low temperatures, the CDW picture is negated by the observation of a metallic Hall contribution, a non-trivial gap structure in STS below $\sim 170$ K and ARPES spectra, that together represent evidence for the onset of the correlated state at $70$ K and the rapid increase of gap size below $\sim 30$ K. The intricate interplay between electronic correlations and the presence of multiple narrow bands near the Fermi level set the stage for metastability and suggest suitability for memristor applications., Comment: 13 pages, 6 figures, pre-print of an article published in Scientific Reports. The final authenticated version is available online at http://dx.doi.org/10.1038/s41598-019-52231-4

This study was designed to better understand the microstructural and phase evolution of lead-free sodium potassium niobate based piezoceramics with a nominal composition (K0.5Na0.5)0.99Sr0.005NbO3 (KNNSr) during pressure-less spark plasma sintering followed by post-annealing in oxygen. The as-sintered samples were dark-coloured and electrically conductive as a result of partial reduction of Nb5+ to Nb4+ and formation of oxygen vacancies confirmed by X-ray photoelectron and Raman spectroscopy. The Rietveld refinement analysis showed that the as-sintered samples contained two perovskite phases with monoclinic Pm unit cell and slightly different unit-cell parameters. The microstructure with sub-micrometre-sized grains unambiguously confirmed that rapid heating and short dwell time hindered the grain growth. We found that post-annealing the samples at 950 °C in oxygen led to improvement in functional properties. The samples became white-coloured, the both perovskite unit cells decreased as a result of re-oxidation, while the microstructure remained essentially unchanged. The KNNSr sintered at nominal sintering temperature of 1300 °C for 3 min and post-annealed possessed a relative density of 88% and dielectric and piezoelectric properties similar to those of the conventionally sintered samples. Our findings contribute to the understanding of pressure-less spark plasma sintering of sodium potassium niobate-based materials and suggest that arrested grain growth and minimisation of alkali evaporation not necessarily lead to dense ceramic.

We present a study of the magnetic phase diagram and the magnetoresistance of a Gd–Tb–Dy–Ho–Lu "ideal" hexagonal high-entropy alloy (HEA), composed of the elements from the heavy half of the rare earth series only. The phase diagram contains an antiferromagnetic (AFM) state, a field-induced ferromagnetic (FM) state above the AFM-to-FM spin-flop transition and a low-temperature spin-glass state. The complex ( H , T ) phase diagram is a result of competition between the periodic potential arising from the electronic band structure that favors periodic magnetic ordering, the substitutional-disorder-induced random local potential that favors spin-glass-type spin freezing in random directions, the Zeeman interaction with the external magnetic field that favors spin alignment along the field direction and the thermal agitation that opposes any spin ordering. The magnetoresistance reflects complexity of the ( H , T ) phase diagram. Its temperature dependence can be explained by a continuous weakening and final disappearance of the periodic potential upon cooling that leads to the destruction of long-range ordered periodic magnetic structures. The magnetoresistance is large only at temperatures, where the AFM and field-induced FM structures are present and exhibits a maximum at the critical field of the AFM-to-FM transition. Within the AFM phase, the magnetoresistance is positive with a quadratic field dependence, whereas it is negative with a logarithmic-like field dependence within the field-induced FM phase. At lower temperatures, the long-range periodic spin order "melts" and the magnetoresistance diminishes until it totally vanishes within the low-temperature spin glass phase. The magnetoresistance is asymmetric with respect to the field sweep direction, reflecting nonergodicity and frustration of the spin system.

The CoCrFeMnNi high-entropy alloy (HEA) is a magnetically concentrated crystalline system with all lattice sites magnetic, containing randomness (five different types of spins are randomly positioned on the lattice) and frustration (a consequence of mixed ferromagnetic and antiferromagnetic interactions). The sample material was prepared as a non-equiatomic, fully random solid solution of the five magnetic elements and we have studied experimentally the nature of the magnetic state. Upon cooling, no long-range magnetic ordering takes place, but the spin system undergoes a kinetic freezing transition to a spin glass phase, where below the spin freezing temperature T f ≈ 20 K, ergodicity of the system is broken. The observed broken-ergodicity phenomena include zero-field-cooled – field-cooled magnetization splitting in low magnetic fields, a frequency-dependent cusp in the ac susceptibility, an ultraslow time-decay of the thermoremanent magnetization and the memory effect, where the state of the spin system reached upon isothermal aging at a certain temperature can be retrieved after a reverse temperature cycle. All these phenomena are associated with the out-of-equilibrium dynamics of a nonergodic, frustrated system of coupled spins that approach thermal equilibrium, but can never reach it on a finite experimental time scale, so that we are observing only transient effects of partial equilibration within localized spin domains.

We address the nature of the collective magnetic state in an ideal high-entropy alloy (HEA), representing a magnetically concentrated system with all lattice sites occupied by localized magnetic moments and containing randomness and frustration due to chemical disorder. Being a “metallic glass on a topologically ordered lattice”, HEAs possess simultaneously the properties of an ordered crystal and an amorphous glass. The influence of this crystal-glass duality on the collective magnetic state was studied experimentally on a hexagonal Tb-Dy-Ho-Er-Tm (TDHET) HEA, composed of rare-earth (RE) elements with zero pair mixing enthalpies that assure completely random mixing of the elements and very similar atomic radii that minimize lattice distortions, representing a prototype of an ideal HEA. The TDHET HEA is characterized by probability distributions of the atomic moments P ( μ ) , the exchange interactions P ( J ) , the magnetocrystalline anisotropy P ( D ) , and the dipolar interactions P ( H d ) . Based on the measurements of the static and dynamic magnetization, the magnetization M ( H ) curves, the thermoremanent magnetization, the specific heat and the magnetoresistance, we found that the collective magnetic state of the TDHET is temperature-dependent, forming a speromagnetic (SPM) state in the temperature range between about 140 and 30 K and an asperomagnetic (ASPM) state below 20 K. In the intermediate temperature range between 30 and 20 K, a spin glass (SG) state is formed, representing a transition state between the speromagnetic and asperomagnetic states. The observed temperature evolution of the magnetic ground state in the TDHET HEA upon cooling in the sequence SPM→SG→ASPM is a result of temperature-dependent, competing magnetic interactions. The distribution of the exchange interactions P ( J ) shifts continuously on the J axis from the high-temperature SPM-type with the average interaction biased towards a net negative value, J ‾ 0 , through the SG-type with J ‾ = 0 , to the low-temperature ASPM-type with J ‾ > 0 . This shift is a band-structure effect, closely linked with the crystallinity of the spin system, which the TDHET HEA shares with the topologically ordered crystals. The probability distributions P ( μ ) , P ( J ) , P ( D ) and P ( H d ) are, on the other hand, a consequence of chemical disorder, a property that the TDHET HEA shares with the amorphous magnets. Both features, the topologically ordered lattice and the amorphous-type chemical disorder essentially determine the magnetic state of an ideal, RE-based HEA.

ABO 3 -type perovskite crystallites with symmetrical crystal structures do not show a tendency to grow in the shape of rods and plates, which are of great scientific interest due to their anisotropic physical properties. A topochemical transformation is one of the most convenient approaches for the preparation of such defined-shape perovskite particles, the functional properties of which can be additionally tailored by the formation of solid solutions. In this study a one-step topochemical conversion reaction from a Bi 4 Ti 3 O 12 template to A-site-substituted complex Ba 1-x Sr x TiO 3 perovskite microplates was investigated in order to understand the mechanism and to determine the compositional, structural and morphological correlations between the template and the final plate-like particles. Based on our finding that Sr incorporates in a 2.7-times larger amount than expected from the initial Ba/Sr ratio (0 1-x Sr x TiO 3 solid-solution composition could be prepared using this topochemical transformation. The tetragonal distortion of the Ba 1-x Sr x TiO 3 plates, expressed as the c/a ratio, was found to decrease linearly from 1.0092 (x = 0) to 1.0037 (x = 0.23), while the compositions with higher x were cubic (c/a=1). According to a piezo-response force microscope (PFM) examination, Ba 1-x Sr x TiO 3 plates with 0 ≤x ≤ 0.175 showed ferroelectric and piezoelectric characteristics. The temperature of the ferroelectric-to-paraelectric phase transition, as determined by differential scanning calorimetry (DSC), linearly decreased from 124 °C (x = 0) to 88 °C (x = 0.11). XRD examinations revealed a strong (001) preferential orientation for the plates (0 ≤ x ≤ 0.11) and the typical (001)/(100) peak splitting indicated the presence of c - and a -domains. The successful preparation and design of Ba 1-x Sr x TiO 3 plates increase the potential of this topochemical transformation for the preparation of plates with a variety of solid-solution compositions and controlled characteristics.

Two different quaternary ammonium cations, methyltriethyl- (MTEA) and tetraethylammonium cations (TEA) were used as templates in the synthesis of pure-silica as well as aluminosilicate ZSM-12 (MTW-type) frameworks. The distribution of the template cations in the 12-membered rings channels in the 1-dimensional framework topology was studied; thus the as-prepared products were characterized by means of X-ray powder diffraction, Raman, transmission FTIR, solid-state NMR spectroscopy, thermogravimetric and elemental analyses and SEM. It was shown that in pure-silica (PS) ZSM-12, TEA cations are well ordered - a superstructure with three-times longer b edge (in comparison to unit cell of empty framework) along the channel is formed, which can be seen by virtue of a few additional peaks in the X-ray powder pattern. Herein we describe that its aluminosilicate counterpart with TEA also contains ordered TEA cations and is isostructural to PS-ZSM-12. Conversely, in both pure-silica and aluminosilicate ZSM-12 frameworks with MTEA, the cations are disordered and no superstructure is formed.

Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop. In an open-porous medium the colouration coincides well with the crystallization and the colour hysteresis widens to about 4 °C. Microencapsulated composite exhibits two crystallization processes, one of them taking place at the bulk crystallization temperature and the other one at about 20 °C lower. Under such conditions the composite is coloured just before the onset of the second crystallization, i.e. about 15 °C below crystallization in the bulk, and the corresponding colour hysteresis widens to 18 °C. The two crystallization forms are thermally independent and have the same crystalline structure. These effects should be taken into account when designing future applications where the phase-changing materials are implemented.

High-temperature reactions during the solid-state synthesis of samples from the (1-x)Na 0.5 Bi 0.5 TiO 3 –xSrTiO 3 system were investigated. Due to the number of chemically different elements, the processing of these ceramics is delicate and requires several firing steps under specific conditions to obtain phase-pure samples. Sintering in an air atmosphere resulted in a macroscopically inhomogeneous microstructure, which is a consequence of incomplete reaction between different secondary phases. However, prolongation of the sintering time aggregated the pores in the sample, while at a higher firing temperature the sample’s secondary phase melted. As a result, the nominal composition was altered, leading to the formation of the Na 2 Ti 6 O 13 secondary phase. Sintering under an increased oxygen pressure of 1 MPa limited the evaporation of the secondary phase. This allowed the completion of the reaction, forming a homogeneous and dense sample. The study provides a set of experimental conditions for the successful preparation of ceramics from the investigated system.

Rare-earth (RE) based hexagonal high-entropy alloys (HEAs) containing elements from the heavy half of the RE series (from Gd to Lu) are considered as prototypes of an ideal HEA, stabilized by the entropy of mixing with completely random distribution of the elements on an almost undistorted hexagonal close-packed (hcp) lattice. Here we present a study of the Ce-Gd-Tb-Dy-Ho hexagonal HEA (abbreviated as HEA-Ce), where a light-RE element Ce is alloyed with four heavy-RE elements. Since the binary mixing enthalpies of Ce with these elements are all zero, random mixing of the elements and an ideal solid solution can also be expected. Contrary to the expectations, a two-phase structure forms in the HEA-Ce, consisting of the majority hcp matrix and the rhombohedral precipitates that occupy a significant fraction of the sample's volume, with both phases having very similar composition. The “ideality” of the HEA-Ce solid solution is very likely compromised by the fact that the crystal structure of Ce is different from the structures of other elements. By performing measurements of the magnetic properties, the specific heat and the electrical resistivity in a magnetic field, we have determined the magnetic state of the HEA-Ce. Long-range-ordered periodic magnetic structures do not form (like they do in the hexagonal HEAs containing heavy-RE elements only), but the magnetic structure breaks up into ferromagnetically (FM) polarized spin domains distributed in size that orient randomly in zero field. The magnetically ordered state of the HEA-Ce can be described as a disordered FM state with a 2nd-order thermodynamic FM phase transition at T C = 140 K. The introduction of Ce did not yield any of the phenomena that are exceptional for the Ce-containing alloys and compounds (mixed valence, heavy-fermion, unconventional superconductivity).

We have investigated the magnetism of CoCrFeNiZr x (x = 0.4–0.5) eutectic high-entropy alloys (HEAs) in relation to their microstructure by XRD, SEM, magnetization, specific heat and electrical resistivity measurements. Two structural phases develop in the CoCrFeNiZr x HEAs, a Zr-free fcc solid solution and a Zr-containing C15 Laves-phase intermetallic compound, where in both phases magnetic transition elements Co, Cr, Fe and Ni substitute each other in a random-like manner. Relative fractions of the two phases change substantially with the Zr concentration. Microstructurally, the two phases form alternatively grown fine lamellar structure typical of eutectic alloys. In addition, bulky dendrites of the fcc solid solution form in large number for the x = 0.40 concentration and in small number for x = 0.45. Two magnetic structures coexist in the CoCrFeNiZr x HEAs. The first is a disordered ferromagnetic (FM) phase that develops in the interior of large dendrites of the fcc solid solution and in some larger lamellas of this phase. The second phase is superparamagnetic-like and originates from the remaining spins of the fcc solid solution fraction, located at the surfaces and in the interfaces, and from all spins of the C15 Laves-phase fraction. The relative magnitude of the disordered FM-state magnetization with respect to the superparamagnetic magnetization in the samples with different Zr concentration is predominantly determined by the volume fraction of the fcc bulky dendrites. There is no one-to-one relation between the two magnetic structures on one side and the two structural components of the CoCrFeNiZr x eutectic mixtures on the other side. The magnetism of multi-phase HEAs containing magnetic elements cannot be described as a compositional average of magnetic properties of the constituent phases.

We present a study of superconductivity in Ta-Nb-Hf-Zr-Ti high-entropy alloys (HEAs) by investigating four samples of different atomic concentrations (equimolar and off-equimolar) and number of components (4 and 5), subjected to different thermal treatments. The structure of the samples varied between a homogeneous random solid solution and a partially ordered nanostructure in the form of a three-dimensional grid of short-range ordered atomic clusters enriched in Zr and Hf that has developed during long-time annealing. Superconductivity was found to be a robust phenomenon, being quite insensitive to the actual structure of the material. All investigated samples were superconducting in the entirety of their volumes. The superconducting transition temperatures T C of the samples are scattered in the range between 5.0 and 7.3 K and this scatter could be related to the degree of structural and chemical inhomogeneity of the samples. In the samples with partially ordered nanostructure, short-range atomic clusters possess a slightly different T C than the Ta- and Nb-rich matrix. Our results also demonstrate the important fact that the formation, stability and structure of a regular (non-ideal) HEA mixture are determined by both, the minimization of the mixing enthalpy that favors local atomic ordering and the maximization of the mixing entropy that favors a random solid solution. The actual equilibrium state achieved during long-time thermal annealing via the atomic diffusion is generally partially ordered, and the resulting nanostructure is a sensitive function of the number of components constituting the HEA, their concentrations, the differences in the atomic radii and the annealing temperature and time. This nanostructure essentially determines the electronic properties of HEA materials.

Physicochemical evaluation of polyethylene oxide (PEO) polymers with various molecular weights was performed at molecular (polymeric dispersion) and bulk level (powders, polymeric films, and tablets) with the aim of specifying polymer critical material attributes with the main contribution to drug release from prolonged-release tablets (PRTs). For this purpose, grades of PEO with low, medium, and high viscosity were used for formulating PRTs with a good soluble drug substance (dose solubility volume 15 ml). The results revealed a good correlation (r2=0.88) between in vivo data (pharmacokinetic parameters: Cmax and AUC) and the elastic property of PEO films determined with the nanoindentation method, demonstrating that film level can also be used for the in vivo prediction of drug dissolution. The study confirmed that polymer molecular weight and its viscosity are the most important critical material attributes affecting drug dissolution (in vitro) and in vivo bioavailability (e.g. Cmax and AUC). Our research revealed that the nanoindentation technique can distinguish well between various types of polymers, classifying PEO as the most ductile and polyvinyl alcohol as the most brittle. Finally, our study provides an approach for the determination of exact physical attributes of PEO as a critical material attribute from clinically relevant data, and it therefore fulfills the basic principles of product development by Quality by Design.

This study was supported by the ERA-NET HarvEnPiez project. The authors would like to thank their national funding agencies (Latvian State Education Development Agency, Slovenian Ministry of Higher Education, Science and Technology, Romanian National Authority for Scientific Research and Innovation, CCCDI-UEFISCDI, project number 49/2016 within PNCDI III – M-ERA NET Program)., The results of experimental and theoretical ab initio study of structural and piezoelectric properties of (Ba,Sr)TiO3 perovskite solid solutions are discussed and compared. Experimentally, plate-like (Ba,Sr)TiO3 particles were synthesized by the topochemical conversion in the molten salt from Bi4Ti3O12 template plates. All dimensions (side length ≈ 1 µm, thickness ≈ 200–400 nm) were well above the critical size necessary for observation of piezo- and ferroelectricity. The first-principles computations of the structural and electromechanical properties of solid solutions were performed with CRYSTAL14 computer code within the linear combination of atomic orbitals (LCAO) approximation, using three advanced hybrid functionals of the density-functional-theory (DFT). Different chemical compositions are considered for the ferroelectric and paraelectric phases. Calculated structural properties of solid solutions in tetragonal and cubic phases are in a very good agreement with experimental data. Experimentally obtained and calculated band gaps are compared for cubic SrTiO3 and tetragonal BaTiO3. BaTiO3/SrTiO3 heterostructures were considered theoretically for different chemical compositions. The calculated piezoelectric properties of solid solutions and heterostructures in ferroelectric phase are compared. It is predicted that both solid solutions and heterostructures improve the piezoelectric properties of the bulk BaTiO3, but solid solutions are more preferable for equal Sr concentrations., ERA-NET HarvEnPiez project; Latvian State Education Development Agency, Slovenian Ministry of Higher Education, Science and Technology, Romanian National Authority for Scientific Research and Innovation, CCCDI-UEFISCDI, project number 49/2016 within PNCDI III – M-ERA NET Program; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Detailed characterization of calcium aluminate rich secondary steel slag derived from two different refining processes of stainless steel production has been performed in order to gain generic knowledge about this by-product, and its behaviour as a supplementary cementitious material. Additionally, slag blended cement composites were investigated and compared to a limestone filler blended cement composites and to a reference cement composites. The results showed that the investigated slag contained several hydraulic phases, mainly in the form of calcium aluminates. In the case of the slag cement composites, a larger proportion of hydration products was observed than in the case of the limestone cement composites, as well as a higher rate of strength increase.

A precise X-ray crystal structure determination of systems that exist in a polycrystalline form often poses a challenge due to several factors that limit the resolution of the diffraction measurement. The location of atoms is usually determined at significantly lower precision than the unit cell parameters, rendering the complete characterization of the structure difficult. This is particularly pronounced when precise location of hydrogen atoms is required, for instance in ionizable biomolecules or in hydrogen bonds. In such cases periodic quantum (DFT) calculations may crucially assist structure determination, because they can reliably predict the location of atoms, provided that the unit cell parameters, the space group and tentative atomic positions are known. In this work we present DFT-assisted structure determination of pentadecafluorooctanoic acid hydrate, a benchmark system featuring short hydrogen bonds (RO...O ≈ 2.5 Å) between acid and water molecules. While Rietveld refinement based solely on powder diffraction data cannot reliably resolve the location of crystal water molecules and even less so the position of hydrogen atoms in the network of hydrogen bonds, periodic DFT optimization yields several minimum energy structures suitable for further refinement. Due to the low experimental resolution and similarity, comparison between model and experimental powder diffraction pattern can barely distinguish between certain structure candidates provided by DFT calculations, but it can rule out those featuring larger misfits. The proposed structure solution is delivered from a tandem application of structure determination from powder diffraction data and DFT optimization, the former providing the unit cell parameters and estimated atomic positions that are finely tuned by DFT. The present strategy can in principle be generalized to other examples of structure determination at relatively low resolution, such as is often the case with biological macromolecules. This work is licensed under a Creative Commons Attribution 4.0 International License.

Sub-solidus phase relations in the ternary CaO–La2O3–TiO2 system at 1400 °C in air were determined. The multi-phase samples were prepared by a solid-state reaction method, whereas the single-phase samples for the structure analysis of selected solid solutions were prepared by a wet-precipitation method in order to provide good homogeneity of the starting mixtures. The phases in the prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The oxides form seven ternary compounds in the equilibrium state, many solid solutions (which extend across a broad concentration region), and a large, single-phase area based on the CaTiO3 solid solution. The structures of several new phases – solid solutions on the tie lines CaTiO3–Ca3La4Ti3O15 and La2TiO5–Ca3La4Ti3O15 – were determined in detail.

Structural information is crucial for understanding and tailoring the materials properties. When the materials are available only in the polycrystalline form, powder diffraction is the method of choice for structure determination. Compared to the single crystal data, the powder pattern contains less information due to the overlap problem and the reduction of the information content is even larger if only the low resolution data are available. Several data analysis approaches are available to address this problem, including reciprocal, direct and dual space methods. They are discussed and illustrated by a number of examples, including cases where other techniques, such as IR and NMR spectroscopy, electron microscopy and crystal-chemical knowledge have to be applied to solve the structure.

We present the synthesis, characterization, and magnetic properties of hematite particles in a peculiar “nanomedusa” morphology. The particles were prepared from an iron-silica complex by a hydrothermal process in a solution consisting of ethyl acetate and ethanol. The particles’ morphology, structure, and chemical composition were investigated by transmission electron microscopy, powder X-ray diffraction, and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The “hairy” particles consist of a spherical-like core of about 100 nm diameter and fibrous exterior composed of thin “legs” of 5 nm diameter grown along one preferential direction. The particles’ cores are crystalline and undergo a magnetic phase transition to a weakly ferromagnetic state at a temperature of 930 K that matches reasonably the Néel temperature of bulk hematite. However, unlike bulk hematite that undergoes Morin transition to an antiferromagnetic state around room temperature and small hematite nanoparticles that are superparamagnetic, the “nanomedusa” particles remain weakly ferromagnetic down to the lowest investigated temperature of 2 K. Each particle thus represents a nanodimensional “hairy” ferromagnet in a very broad temperature interval, extending much above the room temperature. Such high-temperature ferromagnetic nanoparticles are not frequently found among the nanomaterials.

PurposeIn this manuscript the purpose is to present and evaluate the developed non‐destructive method for analysing the phase composition of LTCC Du Pont “Green Tape 951” material fired in the temperature range from 800 to 1,000°C using X‐ray powder diffraction and Rietveld refinement.Design/methodology/approachThe method uses the crystalline Al2O3 which is already present in the material as an internal standard since its mass fraction was previously found to be constant in the described temperature range.FindingsThe results of the non‐destructive analyses and the classical destructive analyses are comparable and the estimated error of the destructive phase analyses and the calculated errors for the non‐destructive phase analyses are of the same order.Practical implicationsThe described method can be used also for analysing another type of LTCC material. In this case it is necessary to check whether the mass fraction of any crystalline phase present in the sample is constant in the given temperature range, because only in this case can it be used as an internal standard for a determination of the phase composition.Originality/valueThe non‐destructive method is a fast and easy approach for analysing the fired samples and is also suitable for controlling the phase composition of LTCC materials on 3D complex structures without destroying them, just by using the X‐ray diffraction patterns collected from their surface.

Low-temperature co-fired ceramic (LTCC) is an important material in the production of ceramic multilayer structures. Large and complex multilayer structures are usually fired at higher temperatures and/or longer firing times compared to the relatively thin LTCC tapes. The firing conditions of LTCC determine the phase composition and the microstructure, which both influence the physical characteristics, such as the mechanical and thermal properties. In this work the effect of the phase composition on the biaxial flexural strength and the temperature coefficient of expansion of the DuPont 951 LTCC is presented. The samples were fired at different temperatures and times to obtain different phase compositions. The phase composition, especially the mass fraction of anorthite, was correlated with the biaxial flexural strength and the thermal coefficient of expansion (TCE). A very long firing time, i.e., 100h at 800 °C, yields, apart from crystalline anorthite, the cristobalite phase. The anorthite that crystalizes from the glass phase in a dense LTCC material changes the crack-propagation mechanism and improves the biaxial flexural strength of the material. The major change in the biaxial flexural strength is observed when the anorthite phase appeared. The increasing mass fraction of anorthite does improve the biaxial flexural strength less drastically. With the increasing mass fraction of the anorthite, decreases of the TCE of the material and a small decrease of the density of the LTCC material occur.

In this work the effect of firing temperature and firing time on the phase composition, microstructure, biaxial flexural strength, and temperature coefficient of expansion (TCE) of low-temperature cofired ceramic (LTCC) material is presented. At temperatures around 700°C the Al2O3 starts to dissolve in a low viscosity glass phase and this takes place up to 800°C, when 10 wt% of Al2O3 ceramic filler is dissolved in the glass phase forming the alumina-enriched area. This area is suitable for the crystallization of anorthite, which nucleates on the Al2O3 particles. The crystallization starts at 875°C and the mass fraction of anorthite increases with increasing temperature until it reaches a plateau value of around 22 wt% at higher temperatures or longer firing times. The biaxial flexural strength of the LTCC increases with increasing firing temperature from 135 MPa (at 800°C) to around 300 MPa (at 900°C). The major effect on the biaxial flexural strength of LTCC is that of porosity. The effect of the amount of anorthite on the LTCC biaxial flexural strength is minor. The TCE of the LTCC decreases from 5.6 × 10−6 to 5.0 × 10−6 K−1 with increasing firing temperatures or times and it is correlated with the anorthite mass fraction, which crystallizes at the expense of a decreasing amount of glass phase in the LTCC.

It has been an established fact that finely ground calcium carbonate represents to a certain extent an active component during the hydration of Portland cement and the formation of calcium monocarboaluminate has been confirmed many times. Additionally, the formation of calcium hemicarboaluminate, as another possible compound, has been mentioned. There is, however, lack of specific information regarding these two compounds: there has been no experimental data on their hydration time-dependent formation, their interrelations, and their amount in a hardened cement paste. This paper describes the time-related formation of hemicarboaluminate and monocarboaluminate and reports for the first time in the literature the conversion of hemicarboaluminate into monocarboaluminate on the basis of X-ray diffraction by following the content of the latter using the Rietveld method. Hemicarboaluminate appears at early hydration times in calcite-containing Portland cement, even in the presence of large amounts of calcium carbonate. As the hydration progresses, a gradual conversion of hemicarboaluminate into monocarboaluminate occurs. The only detectable AFm-type compound present in well-hydrated cement is calcium monocarboaluminate.

Using X-ray diffraction and SEM methods, as well as measurements of the microwave dielectric properties, a section of the ternary Bi2O3–TiO2–WO3 system has been investigated at 1100°C. Within this system the formation of pyrochlore has been detected, and it was revealed that WO3 incorporates into the B sites of the pyrochlore crystal lattice. Charge compensation due to W6+ incorporation occurs primarily via the formation of A site vacancies. With this addition the pyrochlore's unit cell decreases, and reaches its lowest value for ∼13 mol.-% of added WO3. The permittivity of the pyrochlore phase is relatively high and decreases with increasing W content, whereas Q × f increases with increasing W content.

The purpose of this research was to determine the influence of temperature, pH, and the addition of sodium oxide silicium oxide (soso) on the dyeability of cotton warp during the process of dip-dyeing. A simulation of the dip-dyeing technique was used. The results show a negligible influence of dip-dyeing bath temperature on the color yield of cotton warp. Lower pH values of dip-dyeing baths cause better dyeability. Addition of soso has a particular influence on the color yield of cotton warp. As a result, the dip-dyeing procedure is shortened when soso is used. The change of color of dip-dyed cotton warp, depending on different pH of the baths and on the addition of soso, was studied using x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. XRD showed that the dyeing conditions do not affect the crystallographic form of indigo, which is form B in all cases. On the other hand, SEM revealed the reasons for the observed effects in the differences in the morphology of the indigo crystallites.

We report on the synthesis and characterization of new a nano-wire-like material with chemical formula Mo6S4.5I4.5. The material can be synthesized in a single step reaction from elements in bulk quantities. The material has a fur-like appearance and is composed of nanowires that are weakly bound in bundles. Bundles itself can be dispersed using an ultrasonic bath in various organic solvents and water. Elemental analysis, X-ray diffraction, thermal analysis (TG, DTA), and electron microscopy were used to characterize the new material in the shape of nanowires. Due to their monodisperse and metallic nature, molybdenum-sulphur-iodine nanowires are an interesting alternative to carbon nanotubes for some applications.

A study of K x Ba 1− x Ga 2− x Ge 2+ x O 8 ceramics revealed that these solid solutions undergo a monoclinic-to-monoclinic P 2 1 / a ⇔ C 2/ m phase transition. The temperature of this phase transition decreases with an increase in x , in a similar way to the sintering temperature, which decreases from 1100 °C ( x = 0) to 970 °C ( x = 1). The temperature of the P 2 1 / a ⇔ C 2/ m phase transition is below the sintering temperatures of K x Ba 1− x Ga 2− x Ge 2+ x O 8 (0.67 ≤ x ≤ 1) solid solutions, whereas the compositions at lower x ( x = 0.4 and 0) remain in the P 2 1 / a modification over a wide temperature range above the sintering temperature. Compared to the C 2/ m modification of K x Ba 1− x Ga 2− x Ge 2+ x O 8 (0.67 ≤ x ≤ 1), with a permittivity of 6.2–6.9, the P 2 1 / a modifications exhibit permittivities of 5.9–7.0 and three-to-eight times higher Q × f values of ∼100,000 GHz (at ∼12 GHz). The temperature coefficient of the resonant frequency is ∼−25 ppm/K, regardless of the composition.

As an alternative to mechanical alloying, high temperature synthesis (HTS) of ultra-hard, super-abrasive AlMgB 14 was performed under normal pressure. The reaction mixture consisted of elemental aluminium and boron, whereas magnesium was added in the form of a Mg-precursor which liberates elemental magnesium approximately 400 °C above the melting point of magnesium, in this way reducing its evaporation during heating-up. The composition after the conversion was 95 wt.% of AlMgB 14 and 5 wt.% of MgAl 2 O 4 . The synthesized AlMgB 14 baseline powder, as well as mixtures of AlMgB 14 consisting of 30, 50 and 70 wt.% of TiB 2 , were hot pressed to near theoretical density. The various samples produced were characterized for microstructure and hardness. A micro-hardness of 29.4 GPa in hot pressed AlMgB 14 and a maximum Vickers hardness of 30.2 GPa in hot pressed samples of AlMgB 14 reinforced with 70 wt.% of TiB 2 were achieved.

In order to achieve better in-vivo performance of the final dosage form comprising a poorly soluble drug the physicochemical properties of the active pharmaceutical ingredient can be altered not only by changing the solid state form but also through the conversion of their crystal habits. To elucidate this approach in the case of simvastatin, the dissolution behaviour of large crystals with the same internal structure but expressing different crystal habits was studied using atomic force microscope. The obtained differences in the dissolution were explained through the determination of crystal morphology, its orientation and assignation of the molecular functional groups that were emerging on the surface of the dissolving crystal face. The dissolution rates of the particular crystal faces measured in situ by atomic force microscopy were found to be distinctly higher than others. The dissolution rate of single crystals differed as a consequence of higher incidence of more polar crystal faces in case of rod shaped crystals isolated from more hydrophilic solvent mixture which we have established through a thorough research of the single crystal morphology, orientation and the assignation of specific functional groups for each of evolved crystal faces. Izboljšane in-vivo lastnosti končne farmacevtske oblike, ki vsebuje slabo topno zdravilno učinkovino, lahko dosežemo s spreminjanjem fizikalno-kemijskih lastnosti zdravilne učinkovine, ne samo v smislu prilagajanja notranje strukture, temveč tudi preko spremembe kristalnega habitusa. Za pojasnitev tega pristopa smo, na primeru simvastatina, z mikroskopom na atomsko silo spremljali hitrost raztapljanja izoliranih večjih monokristalov, ki so imeli enako notranjo strukturo in so se razlikovali po zunanji obliki kristala. Hitrost raztapljanja določenih kristalnih ploskev je bila bistveno hitrejša glede na ostale. Razlika v hitrosti raztapljanja izoliranih monokristalov je bila posledica večje pojavnosti bolj polarnih kristalnih ploskev v primeru paličastih kristalov, ki smo jih izolirali iz polarnih topil, kar smo ugotovili na osnovi poglobljene raziskave morfoloških lastnosti, orientacije monokristalov in asignacije specifičnih funkcionalnih skupin za vsako izmed izraženih kristalnih ploskev.

Rare earth based equimolar Ho-Dy-Y-Gd-Tb hexagonal high-entropy alloy (HEA) is a prototype of an ideal HEA, stabilized by the entropy of mixing at any temperature with random mixing of elements on the hexagonal close-packed lattice. In order to determine intrinsic properties of an ideal HEA characterized by the enormous chemical (substitutional) disorder on a weakly distorted simple lattice, we have performed measurements of its magnetic and electrical response and the specific heat. The results show that the Ho-Dy-Y-Gd-Tb hexagonal HEA exhibits a rich and complex magnetic field-temperature $(H,T)$ phase diagram, as a result of competition among the periodic potential arising from the electronic band structure that favors periodic magnetic ordering, the disorder-induced local random potential that favors spin glass-type spin freezing in random directions, the Zeeman interaction with the external field that favors spin alignment along the field direction, and the thermal agitation that opposes any spin ordering. Three characteristic temperature regions were identified in the $(H,T)$ phase diagram between room temperature and 2 K. Within the upper temperature region I (roughly between 300 and 75 K), thermal fluctuations average out the effect of local random pinning potential and the spin system behaves as a pure system of compositionally averaged spins, undergoing a thermodynamic phase transition to a long-range ordered helical antiferromagnetic state at the N\'eel temperature ${T}_{N}=180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ that is a compositional average of the N\'eel temperatures of pure Tb, Dy, and Ho metals. Region II (between 75 and 20 K) is an intermediate region where the long-range periodic spin order ``melts'' and the random ordering of spins in the local random potential starts to prevail. Within the low-temperature region III (below 20 K), the spins gradually freeze in a spin glass configuration. The spin glass phase appears to be specific to the rare earths containing hexagonal HEAs, sharing properties of site-disordered spin glasses and geometrically frustrated (site-ordered) spin systems, as a consequence of strongly interacting large abundant spins of four magnitudes (those of Gd, Tb, Dy, and Ho) on the hexagonal lattice, being weakly diluted by nonmagnetic yttrium atoms.

In the present work compact and ground cement composites in which 30% of cement by mass was replaced by ladle slag were investigated for their chemical and physico-mechanical properties. To evaluate long-term environmental impacts, leachability test based on diffusion, which combined both, diffusion and dissolution of contaminants, was performed in water and saline water. Total element concentrations and Cr(VI) were determined in leachates over a time period of 180 days. At the end of the experiment, the mineralogical composition and the physico-mechanical stability of cement composites was also assessed. The results revealed that Cr(III) and Cr(VI) were immobilized by the hydration products formed in the cement composites with the addition of ladle slag. Cr(VI) content originating from the cement was also appreciably reduced by Fe(II) from minerals present in the added ladle slag, which thus had significant positive environmental effects. Among metals, only Mo and Ba were leached in elevated concentrations, but solely in ground cement composites with the addition of ladle slag. Lower V concentrations were observed in leachates of ground than compact composite. It was demonstrated that the presence of ladle slag in cement composites can even contribute to improved mortar resistance. The investigated ladle slag can be successfully implemented in cement composites as supplementary cementitious material.

The synthesis of Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) with high-energy milling was studied by X-ray powder diffraction (XRD) using the Rietveld-refinement method. The results are discussed in terms of the qualitative and quantitative composition of the crystalline and amorphous phases as a function of milling time. The mechano-synthesis of PbO, Nb 2 O 5 , and MgO leads to the formation of perovskite PMN. In the initial stage of milling, particle size reduction and a high degree of amorphization were observed, together with the simultaneous formation of perovskite and pyrochlore-type structures. A mechanism for the formation of PMN by the mechano-synthesis route is proposed.

Moybdenum-based subnanometre diameter nanowires are easy to synthesize and disperse, and they exhibit a variety of functional properties in which they are superior to other one-dimensional materials. However, further progress in the understanding of physical properties and the development of new and specific applications have so far been impeded by the fact that their structure was not accurately known. Here we report on a combination of systematic x-ray diffraction and extended x-ray absorption fine structure experiments, and first-principles theoretical structure calculations, which are used to determine the atomic skeletal structure of individual Mo6S9−xIx (MoSIx) nanowires, their packing arrangement within bundles and their electronic band structure. From this work we conclude that the variations in functional properties appear to arise from different stoichiometry, not skeletal structure. A supplementary data file is available from http://stacks.iop.org/0957-4484/16/1578

We report on the properties of a new air-stable nanowire material with the chemical formula Mo6S3I6 .T he distinguishing features of the material are rapid one-step synthesis, easy isolation and controllable dispersion into small-diameter wire bundles. Elemental analysis, x-ray diffraction, thermogravimetry, differential thermal analysis, Raman scattering and electron microscopy were used to characterize the material.

Niobium oxide (Nb2O5) films and powders have been obtained via the sol-gel route from an NbCl5 precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500 °C and 800 °C, respectively, while at 300 °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb2O5 in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb3-O stretching modes and the appearance of polaron absorption were noted with Li+ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail.

Evolution of the structural and magnetic properties of ZnFe1.95Yb0.05O4 nanoparticles, prepared via a high-energy ball milling route and exposed to further thermal annealing/heating, was assessed in detail and correlation of these properties explored. While as-prepared spinel nanoparticles possess a high degree of inversion, heating of the sample to ∼500 °C is found to rapidly alter the cation distribution from mixed to normal, in agreement with the known cation preferences. Under the same conditions the crystallite size only slowly grows. By further thermal treatment at higher temperatures, the crystallite size is changed more appreciably. An interrelationship among the lattice parameter, octahedral site occupancy, and crystallite size has been established. The observations are (a) both the site occupancy of Fe 3+ at octahedral 16d spinel sites (N16d(Fe 3+ )) and the cubic lattice parameter rapidly increase with an initial increase of the crystallite size, (b) the lattice parameter increases with increasing occupancy, N16d(Fe 3+ ), and (c) there appears to be a critical nanoparticle diameter (approximately 15 nm) above which both the site occupancy and lattice parameter values are saturated. The magnetic behavior of the annealed samples appears to be correlated to the evolution of both the cation distribution and crystallite size, as follows. As-prepared samples and those annealed at lower temperatures show superparamagnetic behavior at room temperature, presumably as a consequence of the Fe 3+ distribution and strong Fe 3+ (8a)−O−Fe 3+ (16d) superexchange interactions. Samples with a nanoparticle diameter greater than 12 nm and with almost normal distributions exhibit the paramagnetic state. The coercive field is found to decrease with an increase of the crystallite size. Partial Yb 3+ /Fe 3+ substitution is found to increase the inversion parameter and saturation magnetization. Detailed knowledge of the thermal evolution of structural/microstructural parameters allows control over the cation distribution and crystallite size and hence the magnetic properties of nanoferrites.

This work studied the phases in the Al corner of the Al–Mn–Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al6Mn does not dissolve Be, whilst λ-Al4Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al15Mn3Be2, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be4AlMn contained more Al than Mn. The atomic ratio Al:Mn was between 1.3:1 and 2:1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, λ–Al4Mn, IQC, and Be4AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.

Different synthesis methods for the preparation of nanocrystalline nickel ferrites are reported: the thermal decomposition of precursors, made of: (i) metal-nitrate salts with carboxylic acids (citric, malonic and tartaric), and (ii) metal-nitrate salts and polyethylene glycol (PEG), in the presence of potassium chloride as a capping agent. The as-prepared gel precursors were characterized by TGA/DTA, while the samples obtained after annealing at 450 degrees C were investigated by FTIR, FESEM, XRD and Mossbauer spectroscopy. Regardless of the type of carboxylic acid used, nanocrystallites prepared by (i) method are similar in size (11-16 nm), while the method (ii) gives crystallites similar to 33 nm in size with negligible microstrain. The differences in the lattice parameter, ranging from 8.3369(2) to 8.3574(2) angstrom, result from cation distribution, nonstoichiometry and structural imperfections in the nickel ferrite nanoparticles. The Mossbauer spectra analysis indicates existence of large distortions of tetrahedral and octahedral sites in these spinel compounds. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The influence of the processing conditions on the structural properties of a selected LTCC material (Du Pont 951) was studied. The samples were fired at different temperatures; after which, the unfired and fired tapes were characterized by X-ray powder diffraction analysis (XRD) and scanning electron microscopy (SEM). The XRD patterns were then refined using the Rietveld method, with an internal standard being used to quantify the ratio between the crystalline and amorphous components. The results show that this LTCC tape is composed of alumina, as a ceramic filler, and crystallizing glass. By increasing the firing temperature the alumina is dissolving in the melted glass phase. The mass fraction of the crystallization product, the anorthite, increased with the firing temperature. The mass fraction of the glass phase firstly increased with the increasing firing temperature due to the dissolution of alumina, but after the start of the crystallization of the anorthite from the glass phase the mass fraction of the glass decreased with a further increase in the firing temperature. The XRD results are supported by microstructural analyses.

Over the last 20 years, the effects of using limestone in Portland cement (PC) have been well studied. The benefits of limestone as a partial replacement for PC are well established. Its economic and environmental advantages of reducing CO2 emissions are well known. For a long time, the limestone has been considered as an inert filler. Recently it has been concluded that limestone serves both as an inert filler and also reacts to a limited extend. The reactivity depends on its fineness (specific surface)[1] and content [2,3]. The question arose, whether a) it is the availability of excess carbonate ion in the hydration system, which determines the degree of influence on the hydration process or b) does the system have its internal capacity to include carbonate ions and the increased availability (more carbonate ions in the solution, embedding the hydrating particles) would not have a significant effect. So the question was if the more soluble carbonates would have more pronounced effect on the hydration of the Portland cement than the limestone, which is only slightly soluble. The influence of slightly soluble (CaCO3, MgCO3, dolomite), medium soluble (Li2CO3) and highly soluble (K2CO3 and KHCO3) carbonates on the hydration of Portland cement was studied using Rietveld analysis. The results indicated that the amount of reacted carbonate in cement hydration at a 15% addition of slightly or medium soluble carbonates does not exceed 5% and is not affected by their solubility; at a 15% addition of the highly soluble carbonate K2CO3 the amount of reacted carbonate is around 6% leading to the conclusion that the system behaves according to the option b). The fugure presents the quantitative analysis of cement hydration at 3, 7, 28 and 90 days of hydration and temperatures of 25 and 400C.