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ABSTRACT Manganese oxides/oxyhydroxides (MnOx) are based on Mnn+O6 and Mnn+O4 polyhedra arranged such as to form compact, channel or layered structures. In geology, they are precious archives of past redox conditions for palaeoclimatic reconstructions; in material sciences, they are used for a variety of applications, from pigments to environmental remediation and energy storage. Thus, the fast, remote and non‐destructive identification of MnOx is critical in several disciplines. Micro‐Raman spectroscopy is often used for this purpose, although a systematic characterization of their stability under the laser beam is still lacking. In this work, we present our results on the behaviour of the most common MnOx having compact and channel structures when a 532‐nm laser with intensity between ~23 μW/μm2 and ~36.8 mW/μm2 is used. The compact structures of manganosite (NaCl‐like) and hausmannite (spinel‐like) are stable up to ~36.8 mW/μm2. The stability of oxides with channel structures depends on channel size, charge of channel cations and valence state of Mn. Hausmannite is the final degradation product of all MnOx with channel structures, irrespective of the starting phase. Pyrolusite, manganite, hollandite and romanéchite are relatively stable under the laser beam, and the transition to the spinel structure occurs above 2.5 mW/μm2 while the degradation of cryptomelane and todorokite starts ~226 μW/μm2. The analysis of MnOx thus needs very accurate experimental conditions to avoid misleading and incorrect phase identifications. Based on our data, we propose an analytical protocol for a proper characterization of these minerals via Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Three-phase polymer composites are promising materials for creating electronic device components. The qualitative and quantitative composition of such composites has a significant effect on their functional, in particular dielectric properties. In this study, ceramic filler K2Ni0.93Ti7.07O16 (KNTO) with Ag coating as conductive additive (0.5, 1.0, 2.5 wt.%) was introduced into the polyvinylidene difluoride (PVDF) polymer matrix in amounts of 7.5, 15, 22.5, and 30 vol.%. to optimize the dielectric constant and dielectric loss tangent. The filler was characterized by X-ray phase analysis, Fourier-transform infrared spectroscopy and Scanning electron microscopy methods. The dielectric constant, dielectric loss tangent, and conductivity of three-phase composites KNTO@Ag-PVDF were studied in comparison with two-phase composites KNTO-PVDF in the frequency range from 102 Hz to 106 Hz. The dielectric constant values of composites containing 7.5, 15, 22.5, and 30 vol.% filler were 12, 13, 17.4, 19.2 for pure KNTO and 13, 19, 25, 31 for KNTO@Ag filler (2.5 wt.%) at frequency 10 kHz. The dielectric loss tangent ranged from 0.111 to 0.340 at a filler content of 7.5 to 30 vol.%. A significantly enhanced balance of dielectric properties of PVDF-based composites was found with K2Ni0.93Ti7.07O16 as ceramic filler for 1 wt.% of silver. Composites KNTO@Ag(1 wt.%)-PVDF can be applied as dielectrics for passive elements of flexible electronics. [ABSTRACT FROM AUTHOR]

Experimental studies of the electrochemical and electrophysical properties of protonated potassium polytitanate and sodium-modified pryderite were carried out using the method of nonlinear impedance spectroscopy. The frequency dependencies of the resistance of the volume of grains and grain boundaries were determined depending on the magnitude of the polarization voltage (DC) and on the value of the perturbation signal (AC).

Some solid solutions with the chemical composition KxFeyTi8-yO16 (KFTO) and a hollandite-like structure were successfully synthesized by modified sol–gel method. The obtained powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ceramic pellets based on KFTO powders were obtained by compressing and sintering at 1080 °C for 4 h. The sinters were characterized by X-ray and impedance spectroscopy. XRD results show that KFTO powders have a mono-phase tetragonal structure at x = 1.4–1.8 and y = 1.4–1.6. However, it was recognized that the hollandite-like phase could be broken during sintering to form TiO2 and Fe2TiO5 crystals distributed throughout the volume of the ceramics. A frequency dependency of dielectric properties for the sinters was studied by impedance spectroscopy. It was found that an increase in the TiO2 (rutile) phase during the sintering contributes to a decrease in dielectric losses. At the same time, the KFTO ceramics with reduced content of potassium had increased permittivity. The contribution of electron-pinned defect dipoles (EPDD) and internal barrier layer capacitance (IBLC) in the permittivity of the obtained ceramics was estimated using the Havriliak–Negami equation. It is shown that the KFTO ceramics have the polydisperse characteristic of dielectric relaxation. The observed grain and grain boundary dipole relaxation times were 1.03 × 10−6 to 5.51 × 10−6 s and 0.197 to 0.687 s, respectively.

Ceramic waste forms are designed to immobilize radionuclides for permanent disposal in geological repositories. One of the principal criteria for the effective incorporation of waste elements is their compatibility with the host material. In terms of performance under environmental conditions, the resistance of the waste forms to degradation over long periods of time is a critical concern when they are exposed to natural environments. Due to their unique crystallographic features and behavior in nature environment as exemplified by their natural analogues, ceramic waste forms are capable of incorporating problematic nuclear waste elements while showing promising chemical durability in aqueous environments. Recent studies of apatite- and hollandite-structured waste forms demonstrated an approach that can predict the compositions of ceramic waste forms and their long-term dissolution rate by a combination of computational techniques including machine learning, first-principles thermodynamics calculations, and modeling using kinetic rate equations based on critical laboratory experiments. By integrating the predictions of elemental incorporation and degradation kinetics in a holistic framework, the approach could be promising for the design of advanced ceramic waste forms with optimized incorporation capacity and environmental degradation performance. Such an approach could provide a path for accelerated ceramic waste form development and performance prediction for problematic nuclear waste elements. [ABSTRACT FROM AUTHOR]

Some solid solutions with the chemical composition KxFeyTi8-yO16 (KFTO) and a hollandite-like structure were successfully synthesized by modified sol–gel method. The obtained powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ceramic pellets based on KFTO powders were obtained by compressing and sintering at 1080 °C for 4 h. The sinters were characterized by X-ray and impedance spectroscopy. XRD results show that KFTO powders have a mono-phase tetragonal structure at x = 1.4–1.8 and y = 1.4–1.6. However, it was recognized that the hollandite-like phase could be broken during sintering to form TiO2 and Fe2TiO5 crystals distributed throughout the volume of the ceramics. A frequency dependency of dielectric properties for the sinters was studied by impedance spectroscopy. It was found that an increase in the TiO2 (rutile) phase during the sintering contributes to a decrease in dielectric losses. At the same time, the KFTO ceramics with reduced content of potassium had increased permittivity. The contribution of electron-pinned defect dipoles (EPDD) and internal barrier layer capacitance (IBLC) in the permittivity of the obtained ceramics was estimated using the Havriliak–Negami equation. It is shown that the KFTO ceramics have the polydisperse characteristic of dielectric relaxation. The observed grain and grain boundary dipole relaxation times were 1.03 × 10−6 to 5.51 × 10−6 s and 0.197 to 0.687 s, respectively. [ABSTRACT FROM AUTHOR]

Three-phase polymer composites are promising materials for creating electronic device components. The qualitative and quantitative composition of such composites has a significant effect on their functional, in particular dielectric properties. In this study, ceramic filler K2Ni0.93Ti7.07O16 (KNTO) with Ag coating as conductive additive (0.5, 1.0, 2.5 wt.%) was introduced into the polyvinylidene difluoride (PVDF) polymer matrix in amounts of 7.5, 15, 22.5, and 30 vol.%. to optimize the dielectric constant and dielectric loss tangent. The filler was characterized by X-ray phase analysis, Fourier-transform infrared spectroscopy and Scanning electron microscopy methods. The dielectric constant, dielectric loss tangent, and conductivity of three-phase composites KNTO@Ag-PVDF were studied in comparison with two-phase composites KNTO-PVDF in the frequency range from 102 Hz to 106 Hz. The dielectric constant values of composites containing 7.5, 15, 22.5, and 30 vol.% filler were 12, 13, 17.4, 19.2 for pure KNTO and 13, 19, 25, 31 for KNTO@Ag filler (2.5 wt.%) at frequency 10 kHz. The dielectric loss tangent ranged from 0.111 to 0.340 at a filler content of 7.5 to 30 vol.%. A significantly enhanced balance of dielectric properties of PVDF-based composites was found with K2Ni0.93Ti7.07O16 as ceramic filler for 1 wt.% of silver. Composites KNTO@Ag(1 wt.%)-PVDF can be applied as dielectrics for passive elements of flexible electronics.

In this work, we investigated the stability trends of actinide-bearing hollandites using density functional theory calculations. Incorporating actinides generally decreased the stability of cesium end-members relative to their barium equivalents. Among the actinides, neptunium-containing structures were consistently the least stable. Curium was the most stable actinide in the +3 oxidation state, followed by americium, plutonium, uranium, and neptunium. Conversely, in the +4 state, uranium-bearing hollandites were the most stable. An inverse correlation between actinide content and stability was consistently observed. [ABSTRACT FROM AUTHOR]

New three-phase composites, destined for application as dielectrics in the manufacturing of passive elements of flexible electronics, and based on polymer (PVDF) matrix filled with powdered ceramics of the hollandite-like (KFTO(H)) structure (5.0; 7.5; 15; 30 vol.%) and carbon (MWCNT) additive (0.5; 1.0; 1.5 wt.% regarding the KFTO(H) amount), were obtained and studied by XRD, FTIR and SEM methods. Chemical composition and stoichiometric formula of the ceramic material synthesized by the sol–gel method were confirmed with the XRF analysis data. The influence of the ceramic and carbon fillers on the electrical properties of the obtained composites was investigated using impedance spectroscopy. The optimal combination of permittivity and dielectric loss values at 1 kHz (77.6 and 0.104, respectively) was found for the compositions containing K1.6Fe1.6Ti6.4O16 (30 vol.%) and MWCNTs (1.0 wt.% regarding the amount of ceramic filler). [ABSTRACT FROM AUTHOR]

In this work, polymer matrix composites with the compositions PTFE/KFTO(H) and PTFE/KFTO(H)@CB and with filler volume fractions of 2.5, 5.0, 7.5, 15, and 30% (without and with carbon modification at a content of 2.5 wt.% regarding ceramic material) were produced by calendering and hot pressing and studied using FTIR, SEM, and impedance spectroscopy methods. Ceramic filler (KFTO(H)) was synthesized using the sol–gel Pechini method. Its structure was investigated and confirmed by the XRD method with following Rietveld refinement. The carbon black (CB) modification of KFTO(H) was carried out through the calcination of a mixture of ceramic and carbon materials in an argon atmosphere. Afterwards, composites producing all the components' structures weren't destroyed according to the FTIR results. The effect of carbon additive at a content of 2.5 wt.% relating to ceramic filler in the system of polymer matrix composites was shown, with permittivity increasing up to ε' = 28 with a simultaneous decrease in dielectric loss (tanδ < 0.1) at f = 103 Hz for composites of PTFE/KFTO(H)@CB (30 vol.%). [ABSTRACT FROM AUTHOR]

Hollandite-based ceramics are mainly produced by the traditional solid-phase method. However, the use of "wet" chemistry can improve its morphological characteristics, increase porosity, etc., as well as change the electrophysical properties. In this study complex oxides with hollandite-type structure in the system K 2 O–MeO–TiO 2 (Me = Mg, Ni, Cu) were synthesized by combustion of citrate–nitrate compositions (a special case of the sol–gel method). The structure of obtained material was studied using the XRD and SEM analysis. While studying the electrophysical properties, it was found that in a stream of hydrogen, the electrical conductivity of hollandites with magnesium and nickel increases significantly (by 2–3 orders of magnitude) over the entire studied temperature range. Thus, ceramics based on these hollandites can be used to create hydrogen sensors. [ABSTRACT FROM AUTHOR]

Ceramic waste forms are designed to immobilize radionuclides for permanent disposal in geological repositories. One of the principal criteria for the effective incorporation of waste elements is their compatibility with the host material. In terms of performance under environmental conditions, the resistance of the waste forms to degradation over long periods of time is a critical concern when they are exposed to natural environments. Due to their unique crystallographic features and behavior in nature environment as exemplified by their natural analogues, ceramic waste forms are capable of incorporating problematic nuclear waste elements while showing promising chemical durability in aqueous environments. Recent studies of apatite- and hollandite-structured waste forms demonstrated an approach that can predict the compositions of ceramic waste forms and their long-term dissolution rate by a combination of computational techniques including machine learning, first-principles thermodynamics calculations, and modeling using kinetic rate equations based on critical laboratory experiments. By integrating the predictions of elemental incorporation and degradation kinetics in a holistic framework, the approach could be promising for the design of advanced ceramic waste forms with optimized incorporation capacity and environmental degradation performance. Such an approach could provide a path for accelerated ceramic waste form development and performance prediction for problematic nuclear waste elements.

[Display omitted] • The ultra-long Rb 0.17 IrO 2 nanowires with both amorphous and crystalline features by interfacial oxidation. • Rb 0.17 IrO 2 exhibits outstanding water oxidation activity with an OER current density of 10 mA cm−2 at 330 mV. • Rb leaching behavior can gradually increase the O 2p center of the interface. • Rb 0.17 IrO 2 nanowires exhibited good activity for OER due to the O-2p centers and increased Ir-O hybridization as a result of partial amorphization. Recently, surface reconstruction derived from Ir-based derivatives could achieve satisfactory oxygen evolution performance. Herein, ultra-long nanowire hollandite structured Rb 0.17 IrO 2 was synthesized and a nano-amorphous layer with a thickness of ∼1.5 nm was achieved by interfacial oxidation treatment. The prepared catalyst exhibits outstanding water oxidation activity with an oxygen evolution reaction (OER) current density of 10 mA cm−2 at 330 mV for robust continuous operation in acidic media. Through the spectroscopic and density functional theory (DFT) theoretical calculations, we demonstrate that the nano-amorphous layers induced by interfacial oxidation on the one-dimensional (1D)-nanowire surface have enhanced O-2p centers and increased Ir-O hybridization compared to the bulk Rb 0.17 IrO 2 phase, which essentially balances the adsorption energy of the intermediates. Effectively incorporating surface reconstruction behavior could significantly improve catalyst activity. This work effectively combines 1D Ir-based materials and surface reconstruction, which provides a strategy for the subsequent full utilization of Ir-based materials applied on OER process. [ABSTRACT FROM AUTHOR]

In this study, we investigated an unusual natural Mn oxide hollandite-group mineral from the Kohare Mine, Iwate Prefecture, Japan, that has predominantly water molecules in the tunnels, with K, Na, Ca, and Ba. The specimens are labeled as type manjiroite, but our analyses show that Na is not the dominant tunnel species, nor is it even the primary tunnel cation, suggesting either an error in the original analyses or significant compositional variation within samples from the type locality. Chemical analyses, X‑ray photoelectron spectroscopy, and thermal gravimetric analysis measurements combined with Rietveld refinement results using synchrotron X‑ray powder diffraction data suggest the chemical formula: (K 0.19 Na 0.17 Ca 0.03 Ba 0.01 H 2 O 1.60 ) ( Mn 5.02 4 + Mn 2.82 3 + Al 0.14 Fe 0.02 ) O 13.47 (OH) 2.53. $\left({{\text{K}}_{0.19}}\text{N}{{\text{a}}_{0.17}}\text{C}{{\text{a}}_{0.03}}\text{B}{{\text{a}}_{0.01}}{{\text{H}}_{2}}{{\text{O}}_{1.60}} \right)\left(\text{Mn}_{5.02}^{4+}\text{Mn}_{2.82}^{3+}\text{A}{{\text{l}}_{0.14}}\text{F}{{\text{e}}_{0.02}} \right){{\text{O}}_{13.47}}{{(\text{OH})}_{2.53}}.$ Our analyses indicate that water is the primary tunnel species, and although water has been reported as a component in natural hollandites, this is the first detailed study of the crystal structure and dehydration behavior of a natural hydrous hollandite with water as the predominant tunnel species. This work underscores the rarity of natural Na-rich hollandite phases and focuses new attention on the role of hydrous components of hollandite-like phases in determining their capacities to exchange or accommodate various cations, such as Li+, Na+, Ba2+, Pb2+, and K+ in natural systems. [ABSTRACT FROM AUTHOR]

This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using for their synthesis the method of pyrolysis of citrate-nitrate compositions. Both single-phase titanates and their mixtures are obtained. This paper presents studies of the morphology and structure of the compounds obtained. The value of their electrical conductivity is measured in the temperature range 150–700°C. It is found that the phase with the lepidocrocite structure exhibits the highest conductivity among the considered compositions in the entire temperature range (Eact. = 0.415 eV). [ABSTRACT FROM AUTHOR]

New three-phase composites, destined for application as dielectrics in the manufacturing of passive elements of flexible electronics, and based on polymer (PVDF) matrix filled with powdered ceramics of the hollandite-like (KFTO(H)) structure (5.0; 7.5; 15; 30 vol.%) and carbon (MWCNT) additive (0.5; 1.0; 1.5 wt.% regarding the KFTO(H) amount), were obtained and studied by XRD, FTIR and SEM methods. Chemical composition and stoichiometric formula of the ceramic material synthesized by the sol–gel method were confirmed with the XRF analysis data. The influence of the ceramic and carbon fillers on the electrical properties of the obtained composites was investigated using impedance spectroscopy. The optimal combination of permittivity and dielectric loss values at 1 kHz (77.6 and 0.104, respectively) was found for the compositions containing K1.6Fe1.6Ti6.4O16 (30 vol.%) and MWCNTs (1.0 wt.% regarding the amount of ceramic filler).

In this work, polymer matrix composites with the compositions PTFE/KFTO(H) and PTFE/KFTO(H)@CB and with filler volume fractions of 2.5, 5.0, 7.5, 15, and 30% (without and with carbon modification at a content of 2.5 wt.% regarding ceramic material) were produced by calendering and hot pressing and studied using FTIR, SEM, and impedance spectroscopy methods. Ceramic filler (KFTO(H)) was synthesized using the sol–gel Pechini method. Its structure was investigated and confirmed by the XRD method with following Rietveld refinement. The carbon black (CB) modification of KFTO(H) was carried out through the calcination of a mixture of ceramic and carbon materials in an argon atmosphere. Afterwards, composites producing all the components’ structures weren’t destroyed according to the FTIR results. The effect of carbon additive at a content of 2.5 wt.% relating to ceramic filler in the system of polymer matrix composites was shown, with permittivity increasing up to ε’ = 28 with a simultaneous decrease in dielectric loss (tanδ < 0.1) at f = 103 Hz for composites of PTFE/KFTO(H)@CB (30 vol.%).

Situated in the western Erzgebirge metallogenetic province (Vogtland, Germany), the Eichigt prospect is associated with several quartz-Mn-Fe-oxyhydroxide veins that are exposed at surface. Bulk-rock geochemical assays of vein material yield high concentrations of Li (0.6–4.1 kg/t), Co (0.6–14.7 kg/t), and Ni (0.2–2.8 kg/t), as well as significant quantities of Mn, Cu, and light rare earth elements, a very unusual metal tenor closely resembling the mixture of raw materials needed for Li-ion battery production. This study reports on the results of a first detailed investigation of this rather unique polymetallic mineralization style, including detailed petrographic and mineralogical studies complemented by bulk rock geochemistry, electron microprobe analyses, and laser ablation inductively coupled mass spectrometry. The mineralized material comprises an oxide assemblage of goethite hematite, hollandite, and lithiophorite that together cement angular fragments of vein quartz. Lithiophorite is the predominant host of Li (3.6–11.1 kg/t), Co (2.5–54.5 kg/t), and Ni (0.2–8.9 kg/t); Cu is contained in similar amounts in hollandite and lithiophorite whereas light rare earth elements (LREE) are mainly hosted in microcrystalline rhabdophane and florencite, which are finely intergrown with the Mn-Fe-oxyhydroxides. 40Ar/39Ar ages (~ 40–34 Ma) of coronadite group minerals coincide with tectonic activity related to the Cenozoic Eger Graben rifting. A low-temperature hydrothermal overprint of pre-existing base metal sulfide-quartz mineralization on fault structures that were reactivated during continental rifting is proposed as the most likely origin of the polymetallic oxyhydroxide mineralization at Eichigt. However, tectonically enhanced deep-reaching fracture-controlled supergene weathering cannot be completely ruled out as the origin of the mineralization. [ABSTRACT FROM AUTHOR]

We present the crystal structure, composition, and occurrence of stöfflerite, the naturally occurring Ca-aluminosilicate with hollandite-type structure. Stöfflerite is a high-pressure polymorph of anorthite and an approved mineral. The type material was found in the shergottitic martian meteorite Northwest Africa 856. Type stöflerite (Sto60Lin40) assumes space group I4/m with unit-cell dimensions a = 9.255(1) Å, c = 2.742(3) Å, V = 235.1(2) Å3, and Z = 2. [ABSTRACT FROM AUTHOR]

The hollandite-like copper doped potassium titanate was synthesized by two-step method, including the potassium polytitanate precursor modification with copper compounds in aqueous solution and the following calcination at 900 °C. The structure of material obtained was studied using the XRD and SEM analysis. The Rietveld method was used to estimate the crystalline unit cell parameters and calculate the exact stoichiometry of K 1. 53 (Cu 0. 76 Ti 7.24)O 16 by refining the atomic occupancies for chemical elements. High-k ceramic materials based on this shollandite-like solid solution were sintered at different temperatures varied in the range from 1000 to 1100 °C. The influence of sintering conditions on electric properties of the obtained ceramics was investigated in a wide frequency range. The contribution of different processes on permittivity was discussed using the electron-pinned defect-dipole (EPDD) model, and the internal barrier layer capacitance (IBLC) model. The optimal conditions to produce modified potassium polytitanate, used as intermediate, as well as optimal sintering conditions which allowed obtaining mono-phase hollandite-like ceramic materials were recognized. It was found that such ceramic materials had high permittivity (ε' ≈ 0.9 × 104 at 10 Hz). Image 1 [ABSTRACT FROM AUTHOR]

The hydrothermal treatment of neutral and acidified KMnO4 solutions at concentration of 0.037–0.093 mol/L and temperature of 120, 170, and 220°С for 24 h leads to selective synthesis of three different manganese dioxide modifications: α-MnO2, δ-MnO2, and β-MnO2. The temperature of hydrothermal treatment and medium acidity has been shown to affect considerably the phase composition of KMnO4 reduction products and reaction yield. The obtained samples of MnO2 have been characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and diffuse reflectance spectroscopy. [ABSTRACT FROM AUTHOR]

Hollandite-type crystals have unique and interesting physical and chemical properties. Here, we report the flux growth of hollandite-type single-crystalline potassium ferrotitanate (KFTO) with faceted surface features from a KCl flux. We varied the flux growth conditions, including the kind of flux, holding temperature, and solute concentration for growing faceted crystallites. KCl was found to be the best flux to grow the single-crystalline KFTO particles, while heating at or above 900°C was needed to yield the KFTO single crystals. The crystal growth was only weakly dependent on the solute concentration. Next, we characterized the grown single crystals and discussed the manner of their growth from the KCl flux. TEM images with clear electron diffraction spots indicated that the KFTO crystals grew along the direction to form microrods ~10 μm in size. DFT calculation results indicated that the surface energy of the (100) face is lower than that of the (001) face. Based on these characterization results, we proposed a possible growth mechanism of the KFTO crystals.

Polymer matrix composites based on ED-20 epoxy resin, hollandite K1.6(Ni0.8Ti7.2)O16 and carbon nanotubes with a variable content of 0.107; 0.213 and 0.425 vol.% were obtained for the first time. Initial components and composites produced were characterized by XRD, XRA, FTIR, SEM and Raman spectroscopy. The dielectric properties of composite materials were measured by impedance spectroscopy and determined by the volume ratio of the composite components, primarily by the concentration of CNTs. At a CNT content of 0.213 vol.% (before percolation threshold), the maximum synergistic effect of carbon and ceramic fillers on the dielectric properties of a composite based on the epoxy resin was found. Three-phase composites based on epoxy resin, with a maximum permittivity at a minimum dielectric loss tangent, are promising materials for elements of an electronic component base.

Raman spectra were collected for an extensive set of well-characterized tunnel-structure Mn oxide mineral species employing a range of data collection conditions. Using various laser wavelengths, such as 785, 633, and 532 nm at low power levels (30–500 μW), as well as the comprehensive database of standard spectra presented here, it is generally possible to distinguish and identify the various tunnel structure Mn oxide minerals. The Raman mode relative intensities can vary significantly as a function of crystal orientation relative to the incident laser light polarization direction as well as laser light wavelength. Consequently, phase identification success is enhanced when using a standards database that includes multiple spectra collected for different crystal orientations and with different laser light wavelengths. For the hollandite-group minerals, the frequency of the Raman mode near 630 cm–1 shows a strong linear correlation with the fraction of Mn3+ in the octahedral Mn sites. With the comprehensive Raman database of well-characterized Mn oxide standards provided here (and available online as Supplemental Materials Deposit item AM-20-87390, Supplemental Material. Deposit items are free to all readers and found on the MSA website, via the specific issue's Table of Contents (go to http://www.minsocam.org/MSA/AmMin/TOC/2020/Aug2020%5fdata/Aug2020%5fdata.html).), and use of appropriate data collection conditions, micro-Raman is a powerful tool for identification and characterization of biotic and abiotic Mn oxide phases from diverse natural settings, including on other planets. [ABSTRACT FROM AUTHOR]

Hollandite‐type TiO2 with uniform submicron‐sized particles was prepared using the treatment of K1.2Ti8O16 by KBrO3 in an H2SO4 solution. The electrode material exhibited a 150 mAh g–1 reversible capacity with an average working potential of 1.75 V vs. Li/Li+. Phase transformations taking place during Li+ (de)intercalation were studied by means of synchrotron X‐ray powder diffraction in operando regime. The lowering of symmetry from tetragonal I4/m to monoclinic I2/m at the beginning of the lithiation was observed. The monoclinic distortion was driven by the Ti3+/Ti4+ charge ordering and the location of the Li+ cations at the hollandite tunnel walls in the five‐fold oxygen coordination. The opposite variation of a and b unit cell parameters during charge‐discharge resulted in a negative overall volume change of –1 % at the lithiated state compared to the initial oxide phase. This value is several times lower than the values for other TiO2 polymorphs such as rutile, anatase or TiO2(B) are. [ABSTRACT FROM AUTHOR]

• Hollandite wasteform fabricated by HIP to immobilise Cs/Sr separated waste. • Phase formation and microstructures were identified at the interaction zone. • Hollandite incorporated minor HIP-canister chemistry at the interaction zone. • No deleterious phases were observed that would reduce wasteform performance. A potential hollandite wasteform for immobilising waste containing Cs, Ba, Sr, and Rb, projected from a solvent extraction process that separates Cs/Sr from spent nuclear fuel, was fabricated via hot isostatic pressing (HIPing) within a stainless-steel (SS) canister at 1250 °C / 30 MPa / 2 h. Before HIPing, 2 wt.% Ti metal was added to the precursor, as a redox control additive. Detailed elemental profiling and microstructural analysis at the interaction zone between the wasteform and the SS HIP canister were thoroughly investigated with transmission electron microscopy (TEM) using a lamella extracted by focused ion beam (FIB) milling, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The interaction zone towards the wasteform was ∼20–30 µm in distance and in this region, a hollandite composition with varying chemistry was observed relative to the bulk wasteform. Moreover, the regular Cr-oxide layer, often observed previously for HIPed Synroc-type materials, was not present due to the achievement of reducing condition by adding Ti-metal as redox additive and simultaneous diffusion of canister material towards the ceramic. Predominant Cr-diffusion was observed with incorporation in the hollandite phase along with minor Fe, Mn and Co from the SS canister. This study provides a detailed understanding of the HIP canister – wasteform interaction zone for a hollandite-rich wasteform design for the first time. Importantly, no deleterious phases were formed that may otherwise reduce the performance of the wasteform. This study further demonstrates the flexibility of HIPing as a consolidation process for the treatment of radioactive wastes. [ABSTRACT FROM AUTHOR]

Electrical transport behavior and structural characteristics directly determine the use of functional ceramic materials in electronic information storage, catalytic conversion, and energy field applications. However, these properties are poorly understood because most of the relevant experiments were performed in a rather narrow temperature range. Herein, we used hollandite‐type KxTi8O16 as an example to systematically study the temperature‐dependent structure and electrical transport properties in a wide temperature range from 25 to 900°C. The electrical transport involves both potassium ionic conduction and electronic conduction. With increasing temperature, the ionic conductivity increases below 800°C and decreases above 800°C. The electronic conductivity displays two maxima at 0.15 S/cm at 400°C and 5.2 × 10−4 S/cm at 800°C. These interesting variations in the conductivities are related to the presence of Ti3+ and the structural transformation from hollandite to a mixture of rutile and jeppeite. The findings reported herein support the potential application of titanium‐based hollandites and provide an understanding of the electrical transport properties of functional ceramic materials. [ABSTRACT FROM AUTHOR]

Differential X‐ray absorption contrast tomography was performed on model ceramic composite systems to image the 3D spatial distributions of Ga and Nd containing phases. The model material systems were fabricated such that they contained two constituent phases. Ga–doped Ba hollandite (Ba1.33Ga2.66Ti5.34O16), and pyrochlore (Nd2Ti2O7) which are under consideration as nuclear waste immobilization matrices. Two complementary techniques have been used to characterize the 3D distribution of phases. The analysis suggests that the 3D spatial distributions of hollandite and pyrochlore can be readily identified through the distributions Ga and Nd, respectively. These results represent a critical development towards characterizing the complex microstructure inherent to practical materials such as multiphase ceramic composite waste forms. Moreover, these methods can be applied to elucidate microstructural features that fundamentally determine the performance and properties of complex systems, which is central to the design of durable waste forms as well as many other real materials such fuel cells, batteries, ultra‐high temperature ceramics. [ABSTRACT FROM AUTHOR]

In this paper, a sol-spray pyrolysis route was employed to fabricate (Cs, Ba)-hollandite ceramic waste forms. The high-phase purity (Cs0.8−xBa0.4+x)(Al1.6+xTi6.4−x)O16 (0 ≤ x ≤ 0.4) ceramics were synthesized at 1050 °C using the produced powders by sol-spray pyrolysis. The results show that all samples show tetragonal hollandite with rod morphology. Additionally, the sintered (Cs, Ba)-hollandite ceramics exhibit a good chemical durability. The normalized release rates of Cs and Ba were < 10−2 g m−2 d−1 after 14 days. These results indicate that hollandite ceramics are promising candidate for immobilizing radioactive cesium. [ABSTRACT FROM AUTHOR]

The radiation damage tolerance of nuclear waste forms is dependent on the material's resistance to defect formation and its ability to accommodate structural distortions that arise from defect creation. This study illustrates how the radiation tolerance of hollandite can be improved thorough compositional control of cesium stoichiometry. A hollandite series with the general form Ba x Cs y Zn x+y/2 Ti 8-x-y/2 O 16 (0 < x < 1.33; 0 < y < 1.33) was exposed to heavy ion (Kr2+) irradiation at 27 °C, 100 °C, 200 °C and 300 °C followed by characterization with grazing incidence X-ray diffraction, transmission electron microscopy, and aqueous leaching tests. After exposure to 400 keV or 1 MeV Kr2+ irradiation, hollandite exhibited an onset of amorphization near 0.14 dpa and full amorphization ranging from 0.21 to 0.54 dpa depending on the cesium content. The radiation tolerance increased at elevated temperatures with a critical amorphization temperature between 200 °C and 300 °C. Elemental leaching decreased with increasing cesium content. Irradiated samples exhibited twice the fraction of cesium release compared to pristine samples. Experimental results also showed that cesium release from irradiated samples was at a minimum for the Ba 0.33 Cs 1.00 Zn 0.83 Ti 7.17 O 16 sample. • Cesium incorporation increased hollandite's radiation and leaching stability. • Critical dose for amorphization doubled after full cesium substitution. • Critical amorphization temperature for hollandite was between 200 and 300 °C. • Irradiation doubled fractional cesium released during leaching. [ABSTRACT FROM AUTHOR]

Abstract The effects of fission product transmutation on the structural stability of ceramic waste forms are a critical concern due to the changes of valence and ionic size, which can impair the stability of the host matrices. In this study, [Cs x Ba y ][Ti3+ 2 y + x Ti4+ 8-2 y - x ]O 16 (0.3 ≤ x , y ≤ 0.75) ceramics were designed and successfully synthesized to immobilized 137Cs and its daughter product 137Ba. The evolution of phase and microstructure of the hollandite-ceramic waste forms were investigated by the substitution of Ba2+ into the Cs+ site and the incorporation of Ti3+ for charge compensation. The results show that the prepared hollandite ceramics exhibit excellent capacity to accommodate Cs+ and Ba2+ in its lattice while retaining a stable crystalline structure with a compact microstructure. Additionally, all elements of Cs, Ba, Ti and O homogeneously distributed in the sintered hollandite ceramics. These results further indicate that hollandite ceramics are a promising candidate for selective and durable immobilization of radioactive cesium. [ABSTRACT FROM AUTHOR]

Abstract [Cs x Ba y ][(Al3+,Ti3+) 2 y + x Ti4+ 8-2 y - x ]O 16 (0.4 ≤ x , y ≤ 0.8) ceramics were synthesized to investigate the substitution effects of Ba2+ for Cs+ on the stability of hollandite-ceramic waste forms. It was found that the substitution of Ba2+ for Cs+ in the (Cs,Ba)-hollandite system does not cause substantial variation in the crystallographic phase and microstructure. The normalized release rates of Cs and Ba at 90 °C in deionized water were < 0.005 g m−2 d−1 after 28 days. These results indicate that hollandite ceramics are an ideal host for permanent radioactive caesium disposal. [ABSTRACT FROM AUTHOR]

Manganese (Mn) based oxide materials are regarded as one of the favorable electrode materials, exhibiting a high energy density, low‐cost and environmental benignity. In this work, we focus on synthesizing hollandite Na−Mn−O composites as potential supercapacitor electrode materials by a facile molten salt technique. The structure and the morphology of the Na−Mn−O system were significantly influenced by the synthesis temperature. The Na−Mn−O composite synthesized at 550 °C (Na−Mn−O 550) demonstrates a distinct structure and a mixed morphology of nanorods and nanoparticles. The Na−Mn−O 550 composite exhibits the best electrochemical performance with 306.0 F/g at 0.5 A/g and maintains 80.7 % capacity after 3000 charge‐discharge times at 5 A/g. The largest specific capacitance of 64.0 F/g (0.3 A/g) and high energy density of 20.0 Wh/kg (226.1 W/kg) were achieved in the assembled asymmetric supercapacitor device based on the Na−Mn−O 550 and active carbon. Moreover, a long‐cycling lifetime with 92.9 % retention after 10000 cycles was performed, which holds broad prospect for practical application in high performance energy storage devices. Synthesis of Na‐Mn‐O composites: Na‐Mn−O composites are synthesized by a facile molten salt technique as electrode material for supercapacitors. The growth mechanism, morphology and electrochemical properties of the composites are discussed. [ABSTRACT FROM AUTHOR]

Identification of catalytically active species and reaction pathway in catalytic solid (catalyst)-solid (reactant) reactions is a nontrivial task as exemplified in diesel soot oxidation (combustion), the technology for control of diesel particulate emissions. A physical contact between catalytically active species and solid soot is usually deemed necessary. Herein, thermally-stable hollandite-type α-MnO 2 (K x Mn 8 O 16 ) nanorod catalysts have been synthesized with one-dimensional tunnel structures partially filled with relatively mobile K cations. These tunnel-confined quasi free K cations are revealed to be responsible for the catalytic soot oxidation activity, proving that physical contact between soot and K cations is unnecessary for solid-solid reaction. A novel catalyst, K y Ti 8 O 16 has been successfully designed to boost the catalytic activity in TiO 2 toward soot oxidation by engineering a K-contained hollandite-type isostructure. [ABSTRACT FROM AUTHOR]

Mass cobalt-rich ferromanganese microcrusts and nodules similar in morphology and chemical composition to cobalt-rich ferromanganese deep-ocean crusts were found in Cenozoic volcanic rocks in southern Primorye. Research has shown that ore genesis of this type is genetically related to argillization and destruction of siliceous rocks by CO 2 -rich fluids, which is confirmed by experimental data on carbon erosion of iron-containing materials. Two types of this fluid ore genesis are recognized: (1) relatively high-temperature (vapor-condensate), related to late volcanic processes and fracture gas infiltration, and (2) low-temperature (vapor-liquid-condensate), controlled by degassing followed by carbon mobilization (gasification). Primarily colloidal ferromanganese segregations have high contents of Co, Ni, Pb, Cu, and Ce, typical of oceanic ore genesis. Regardless of the concentrations of these metals in the protoliths, their contents in microcrusts are similar ( n -10 n wt.%). This indicates the same ore genesis mechanism and similar sorption properties of the colloidal ferromanganese material formed. Barium- and cerium-rich ferromanganese microcrusts and nodules are abundant. Condensed drops of iron-containing platinum were found in apobasaltic nickel-rich ferromanganese segregations. There is a cerium paradox expressed as a minimum or a total lack of cerium among rare-earth phosphates associated with ferromanganese microcrusts. Fluid destruction and oxide metallization of ocean-floor basalts are assumed to be the main source of metals for oceanic ferromanganese crusts and nodules. [ABSTRACT FROM AUTHOR]

We conducted high-pressure experiments in plagioclase with different anorthite contents at 18–27 GPa and 25–1750 °C using both a laser-heated diamond anvil cell and a Kawai-type multi-anvil apparatus to clarify the formation conditions of the hollandite phase in shocked chondritic and Martian meteorites. Lingunite (NaAlSi 3 O 8 -rich hollandite) was found first to crystallize from amorphous oligoclase as a metastable phase before decomposing into the final stable state. This process might account for the origin of lingunite found along with maskelynite in shocked chondritic meteorites. Metastable lingunite appeared at ∼20–24 GPa and ∼1100–1300 °C in laboratory tests lasting tens of minutes; however, it might also form at the higher temperatures and shorter time periods of shock events. In contrast, the hollandite phase was not observed during any stage of crystallization when using albite or labradorite as starting materials. The formation process of (Ca,Na)-hollandite in the labradorite composition found in Martian shergottites remains unresolved. The orthoclase contents of the hollandite phase both in shocked meteorites (2.4–8.2 mol%) and our oligoclase sample (3.9 mol%) are relatively high compared to the albite and labradorite samples (0.6 and 1.9 mol%, respectively). This might critically affect the crystallization kinetics of hollandite phase. [ABSTRACT FROM AUTHOR]

We have investigated a tunnel-type β-FeOOH cathode material for rapid sodium storage. Rietveld refinement of the X-ray diffraction (XRD) data obtained for β-FeOOH indicated that the structure was stabilized into [2 × 2] hollandite tunnel structure, and the adhesion of the β-FeOOH onto carbon nanotubes (CNTs) led to a high electrical conductivity of 3 S cm −1 . As a result, the β-FeOOH/CNTs composite electrode showed excellent electrode performance, with a discharge capacity of 205 mAh g −1 and a coulombic efficiency of 88.5% in the voltage range of 1.1–4 V during the first cycle, 131 mAh g −1 after 200 cycles, and a capacity retention of 70% over 300 cycles at 10 C (1920 mA g −1 ). Based on the XRD, X-ray absorption, and time-of-flight secondary-ion mass spectroscopy results, we suggest a new conversion mechanism for the β-FeOOH cathode material in Na cells, namely, FeOOH + Na + + e - → FeO + NaOH. This conversion reaction produces NaOH as a byproduct, and the reaction is fairly reversible even at 10 C-rates. [ABSTRACT FROM AUTHOR]

Radiation damage was simulated in multiphase titanate-based ceramic waste forms using an ion accelerator to generate high energy alpha particles (He + ) and an ion implanter to generate 7 MeV gold (Au 3+ ) particles. X-ray diffraction and transmission electron microscopy were used to characterize the damaged surfaces and nearby regions. Simulated multiphase ceramic waste forms were prepared using two processing methods: spark plasma sintering and melt-processing. Both processing methods produced ceramics with similar phase assemblages consisting of hollandite-, zirconolite/pyrochlore-, and perovskite-type phases. The measured heavy ion (Au 3+ ) penetration depth was less in spark plasma sintered samples than in melt-processed samples. Structural breakdown of the hollandite phase occurred under He + irradiation indicated by the presence of x-ray diffraction peaks belonging to TiO 2 , BaTiO 5 , and other hollandite related phases (Ba 2 Ti 9 O 20 ). The composition of the constituent hollandite phase affected the extent of damage induced by Au 3+ ions. [ABSTRACT FROM AUTHOR]

Hollandite-rich multiphase waste form compositions processed by melt-solidification and spark plasma sintering (SPS) were characterized, compared, and validated for nuclear waste incorporation. Phase identification by x-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) confirmed hollandite as the major phase present in these samples along with perovskite, pyrochlore and zirconolite. Distribution of selected elements observed by wavelength dispersive spectroscopy (WDS) maps indicated that Cs formed a secondary phase during SPS processing, which was considered undesirable. On the other hand, Cs partitioned into the hollandite phase in melt-processed samples. Further analysis of hollandite structure in melt-processed composition by selected area electron diffraction (SAED) revealed ordered arrangement of tunnel ions (Ba/Cs) and vacancies, suggesting efficient Cs incorporation into the lattice. [ABSTRACT FROM AUTHOR]

Lingunite (hollandite with Na contents of 80-85 mol%) discovered in the shock veins of strongly shocked meteorites is an important signature of shock metamorphism. To seek the stability region of lingunite, phase relations in the system KAlSiO-NaAlSiO have been investigated by multi-anvil experiments at pressures of 20-23 GPa and temperatures of 1873 and 2273 K. Phase assemblages of hollandite + jadeite + stishovite, hollandite + calcium ferrite-type NaAlSiO + stishovite and hollandite single phase have been recovered, depending on the pressure-temperature conditions and the compositions of starting materials. Both pressure and temperature have large effects on the solubility of Na in hollandite, and hollandite with 79 mol% Na, similar to the natural lingunite in terms of Na content, has been firstly synthesized at 22 GPa and 2273 K. The stability region of KNaAlSiO hollandite is comparable to the typical pressure-temperature conditions of the shock veins of strongly shocked meteorites (20-25 GPa and 2273-2500 K). [ABSTRACT FROM AUTHOR]

Hollandite solid solutions along the A-site compositional range from the pure barium end-member Ba1.33Ga2.66Ti5.34O16 to the pure cesium end-member Cs1.33Ga1.33Ti6.67O16 have been synthesized using a solid-state reaction technique. The crystal structure of the hollandite across the entire compositional range remained in the I4 /m space group. Structural evolution was resolved by neutron diffraction, total scattering data, and density functional theory calculations. A trend of decreasing thermodynamic stability with smaller tunnel cations was attributed to increased structural distortion observed in the system. In addition, the tunnel cations' local environment was studied in the eightfold coordinated oxygen cavities. Local binding features of the tunnel cations reveals that the hollandite structure can strongly stabilize tunnel cations, even at elevated temperatures up to 500 K. [ABSTRACT FROM AUTHOR]