Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO4 Photocatalyst.

The thermal transformation of zircon to scheelite in BiVO4 was studied by in-situ Synchrotron X-ray diffraction and TGA/FTIR analysis. Upon heating, the tetragonal zircon polymorph of BiVO4 (tz-BiVO4) transitioned to the tetragonal scheelite (ts-)polymorph between 693-773 K, then to monoclinic fergusonite (mf) polymorph upon cooling. An anomaly in thermal expansion was observed between 400-500 K, associated with loss of H2O/NH4+. Heating tz-BiVO4 resulted in contraction of the V-O bond distance and VO4 polyhedra volume due to rotation of the VO4. Attempts to study this by neutron diffraction failed due to the large incoherent scatter from the hydrogenous species. Efforts to remove these species while maintaining the tz-BiVO4 structure were unsuccessful, suggesting they play a role in stabilizing the zircon polymorph. The local structure of both mf-BiVO4 and tz-BiVO4 were investigated by X-ray Pair Distribution Function analysis.

Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO4.

Pair distribution function (PDF) analysis of the scheelite-type material PbWO4 reveals previously unidentified short-range structural distortions in the PbO8 polyhedra and WO4 tetrahedra not observed in the similarly structured CaWO4. These local distortions are a result of the structural influence of the Pb2+ 6s2 lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF). This illustrates the importance of neutron PDF (NPDF) in the study of such materials. First-principles density function theory (DFT) calculations show that the Pb2+ 6s2 electrons are hybridized with the O2- 2p electrons near the Fermi level. The presence of local-scale distortions has previously been neglected in studies of structure-functionality relationships in PbWO4 and other scheelite-structured photocatalytic materials, including BiVO4, and this observation opens new avenues for their optimization.

Tetrahedra Rotational and Displacive Disorder in the Scheelite-Type Oxide CsReO4.

Scheelite-type metal oxides are a notable class of functional materials, with applications including ionic conductivity, photocatalysis, and the safe storage of radioactive waste. To further engineer these materials for specific applications, a detailed understanding of how their properties can change under different conditions is required─not just in the long-range average structure but also in the short-range local structure. This paper outlines a detailed investigation of the metal oxide CsReO4, which exhibits an uncommon orthorhombic Pnma pseudo-scheelite-type structure at room temperature. Using synchrotron X-ray diffraction, the average structure of CsReO4 is found to undergo a transformation from the orthorhombic Pnma pseudo-scheelite-type structure to the tetragonal I41/a scheelite-type structure at ∼440 K. In the X-ray pair distribution function analysis, lattice strain and rotations of the ReO4 tetrahedra are apparent above 440 K despite the increase in long-range average symmetry, revealing a disconnect between the structural models at different length scales. This study demonstrates how the bonding requirements and ionic radii of the A-site cation can induce disorder that is detectable at different length scales, affecting the physical properties of the material.

Resolving Fast Relative Kinetics in Inorganic Solid-State Synthesis.

Solid-state syntheses are generally regarded as being slow, limited by transport, and, as such, are often only stopped to check the products after many hours at high temperature. Here, using a custom-designed reactor to rapidly initiate solid-state syntheses, we are able to capture the earliest stages of a reaction using in situ X-ray scattering. For the reaction of TiO2 and Li2CO3 to form spinel lithium titanate (Li4Ti5O12)─an anode material for fast-charging applications─we capture two distinct kinetic regimes, including fast initial kinetics in the first seconds-minutes of the reaction that account for significant product formation. We use an Avrami model to compare the reaction at high temperatures (700-750 °C), which results in the rapid formation of Li4Ti5O12 within minutes, and lower temperatures (482 °C), consistent with conditions that might be chosen based on "Tamman's rule", a common heuristic. Our analysis reveals characteristic Avrami slopes (i.e., dimensionalities) for each step in the chemical transformation. We anticipate that the fast initial reaction kinetics found here are likely to be common in the synthesis of other materials used in battery electrodes, solid-state electrolytes, ion-conductive membranes, etc. where ion transport is a prerequisite for functionality.

A protein kinase C α and ß inhibitor blunts hyperphagia to halt renal function decline and reduces adiposity in a rat model of obesity-driven type 2 diabetes.

Type 2 diabetes (T2D) and its complications can have debilitating, sometimes fatal consequences for afflicted individuals. The disease can be difficult to control, and therapeutic strategies to prevent T2D-induced tissue and organ damage are needed. Here we describe the results of administering a potent and selective inhibitor of Protein Kinase C (PKC) family members PKCα and PKCß, Cmpd 1, in the ZSF1 obese rat model of hyperphagia-induced, obesity-driven T2D. Although our initial intent was to evaluate the effect of PKCα/ß inhibition on renal damage in this model setting, Cmpd 1 unexpectedly caused a marked reduction in the hyperphagic response of ZSF1 obese animals. This halted renal function decline but did so indirectly and indistinguishably from a pair feeding comparator group. However, above and beyond this food intake effect, Cmpd 1 lowered overall animal body weights, reduced liver vacuolation, and reduced inguinal adipose tissue (iWAT) mass, inflammation, and adipocyte size. Taken together, Cmpd 1 had strong effects on multiple disease parameters in this obesity-driven rodent model of T2D. Further evaluation for potential translation of PKCα/ß inhibition to T2D and obesity in humans is warranted.

MANF stimulates autophagy and restores mitochondrial homeostasis to treat autosomal dominant tubulointerstitial kidney disease in mice.

Misfolded protein aggregates may cause toxic proteinopathy, including autosomal dominant tubulointerstitial kidney disease due to uromodulin mutations (ADTKD-UMOD), a leading hereditary kidney disease. There are no targeted therapies. In our generated mouse model recapitulating human ADTKD-UMOD carrying a leading UMOD mutation, we show that autophagy/mitophagy and mitochondrial biogenesis are impaired, leading to cGAS-STING activation and tubular injury. Moreover, we demonstrate that inducible tubular overexpression of mesencephalic astrocyte-derived neurotrophic factor (MANF), a secreted endoplasmic reticulum protein, after the onset of disease stimulates autophagy/mitophagy, clears mutant UMOD, and promotes mitochondrial biogenesis through p-AMPK enhancement, thus protecting kidney function in our ADTKD mouse model. Conversely, genetic ablation of MANF in the mutant thick ascending limb tubular cells worsens autophagy suppression and kidney fibrosis. Together, we have discovered MANF as a biotherapeutic protein and elucidated previously unknown mechanisms of MANF in the regulation of organelle homeostasis, which may have broad therapeutic applications to treat various proteinopathies.

A platform to reproducibly evaluate human colon permeability and damage.

The intestinal epithelium comprises diverse cell types and executes many specialized functions as the primary interface between luminal contents and internal organs. A key function provided by the epithelium is maintenance of a barrier that protects the individual from pathogens, irritating luminal contents, and the microbiota. Disruption of this barrier can lead to inflammatory disease within the intestinal mucosa, and, in more severe cases, to sepsis. Animal models to study intestinal permeability are costly and not entirely predictive of human biology. Here we present a model of human colon barrier function that integrates primary human colon stem cells into Draper's PREDICT96 microfluidic organ-on-chip platform to yield a high-throughput system appropriate to predict damage and healing of the human colon epithelial barrier. We have demonstrated pharmacologically induced barrier damage measured by both a high throughput molecular permeability assay and transepithelial resistance. Using these assays, we developed an Inflammatory Bowel Disease-relevant model through cytokine induced damage that can support studies of disease mechanisms and putative therapeutics.

MANF stimulates autophagy and restores mitochondrial homeostasis to treat toxic proteinopathy.

Misfolded protein aggregates may cause toxic proteinopathy, including autosomal dominant tubulointerstitial kidney disease due to uromodulin mutations (ADTKD- UMOD ), one of the leading hereditary kidney diseases, and Alzheimer’s disease etc. There are no targeted therapies. ADTKD is also a genetic form of renal fibrosis and chronic kidney disease, which affects 500 million people worldwide. For the first time, in our newly generated mouse model recapitulating human ADTKD- UMOD carrying a leading UMOD deletion mutation, we show that autophagy/mitophagy and mitochondrial biogenesis are severely impaired, leading to cGAS- STING activation and tubular injury. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a novel endoplasmic reticulum stress-regulated secreted protein. We provide the first study that inducible tubular overexpression of MANF after the onset of disease stimulates autophagy/mitophagy and clearance of the misfolded UMOD, and promotes mitochondrial biogenesis through p-AMPK enhancement, resulting in protection of kidney function. Conversely, genetic ablation of endogenous MANF upregulated in the mutant mouse and human tubular cells worsens autophagy suppression and kidney fibrosis. Together, we discover MANF as a novel biotherapeutic protein and elucidate previously unknown mechanisms of MANF in regulating organelle homeostasis to treat ADTKD, which may have broad therapeutic application to treat various proteinopathies.

Molecular and Functional Characterization of Human Intestinal Organoids and Monolayers for Modeling Epithelial Barrier.

BACKGROUND: Patient-derived organoid (PDO) models offer potential to transform drug discovery for inflammatory bowel disease (IBD) but are limited by inconsistencies with differentiation and functional characterization. We profiled molecular and cellular features across a range of intestinal organoid models and examined differentiation and establishment of a functional epithelial barrier. METHODS: Patient-derived organoids or monolayers were generated from control or IBD patient-derived colon or ileum and were molecularly or functionally profiled. Biological or technical replicates were examined for transcriptional responses under conditions of expansion or differentiation. Cell-type composition was determined by deconvolution of cell-associated gene signatures and histological features. Differentiated control or IBD-derived monolayers were examined for establishment of transepithelial electrical resistance (TEER), loss of barrier integrity in response to a cocktail of interferon (IFN)-γ and tumor necrosis factor (TNF)-α, and prevention of cytokine-induced barrier disruption by the JAK inhibitor, tofacitinib. RESULTS: In response to differentiation media, intestinal organoids and monolayers displayed gene expression patterns consistent with maturation of epithelial cell types found in the human gut. Upon differentiation, both colon- and ileum-derived monolayers formed functional barriers, with sustained TEER. Barrier integrity was compromised by inflammatory cytokines IFN-γ and TNF-α, and damage was inhibited in a dose-dependent manner by tofacitinib. CONCLUSIONS: We describe the generation and characterization of human colonic or ileal organoid models capable of functional differentiation to mature epithelial cell types. In monolayer culture, these cells formed a robust epithelial barrier with sustained TEER and responses to pharmacological modulation. Our findings demonstrate that control and IBD patient-derived organoids possess consistent transcriptional and functional profiles that can enable development of epithelial-targeted therapies.

Tetrahedral Displacive Disorder in the Scheelite-Type Oxide RbReO4.

Oxides exhibiting the scheelite-type structure are an important class of functional materials with notable applications in photocatalysis, luminescence, and ionic conductivity. Like all materials, understanding their atomic structure is fundamental to engineering their physical properties. This study outlines a detailed structural investigation of the scheelite-type oxide RbReO4, which exhibits a rare long-range phase transition from I41/a to I41/amd upon heating. Additionally, in the long-range I41/a model, the Re-O tetrahedral distance undergoes significant contraction upon warming. Recent studies of other scheelite oxides have attributed this apparent contraction to incoherent local-scale tetrahedral rotations. In this study, we use X-ray pair distribution function analysis to show that RbReO4 undergoes a unique symmetry-lowering process on the local scale, which involves incoherent tetrahedral displacements. The rare I41/a to I41/amd long-range phase transition was found to occur via a change from static to dynamic disorder on the local scale, which is due to the combination of the size of the A-site cation and lattice expansion. This demonstrates how careful manipulation of the ionic radius of the A-site in the scheelite structure can be used to induce local-scale disorder, which has valuable implications for tailoring the physical properties of related materials.

Understanding the Re-entrant Phase Transition in a Non-magnetic Scheelite.

The stereochemical activity of lone pair electrons plays a central role in determining the structural and electronic properties of both chemically simple materials such as H2O, as well as more complex condensed phases such as photocatalysts or thermoelectrics. TlReO4 is a rare example of a non-magnetic material exhibiting a re-entrant phase transition and emphanitic behavior in the long-range structure. Here, we describe the role of the Tl+ 6s2 lone pair electrons in these unusual phase transitions and illustrate its tunability by chemical doping, which has broad implications for functional materials containing lone pair bearing cations. First-principles density functional calculations clearly show the contribution of the Tl+ 6s2 in the valence band region. Local structure analysis, via neutron total scattering, revealed that changes in the long-range structure of TlReO4 occur due to changes in the correlation length of the Tl+ lone pairs. This has a significant effect on the anion interactions, with long-range ordered lone pairs creating a more densely packed structure. This resulted in a trade-off between anionic repulsions and lone pair correlations that lead to symmetry lowering upon heating in the long-range structure, whereby lattice expansion was necessary for the Tl+ lone pairs to become highly correlated. Similarly, introducing lattice expansion through chemical pressure allowed long-range lone pair correlations to occur over a wider temperature range, demonstrating a method for tuning the energy landscape of lone pair containing functional materials.

Eight-year retrospective study investigating tooth survival after primary non-surgical root canal treatment in a UK military cohort.

INTRODUCTION: Root canal treatment (RCT) plays an important role in preserving the dentition by deferring other invasive treatments. Data on tooth survival and predictive factors for tooth loss after RCT in the military cohort are lacking. This investigation aimed to determine the proportion of teeth surviving in an 8-year period after RCT and identify potential predictive factors for tooth loss in a UK military cohort. METHODOLOGY: A retrospective review of an integrated electronic health record for military patients who had received RCT was performed in a random sample of 205 patients (n=219 root-filled teeth) who had received RCT between 1 January 2011 and 1 January 2012. Tooth survival was defined as tooth presence, regardless of signs or symptoms, and measured from the point of root filling until either the end of the designated study period or time of extraction. Survival was evaluated using Kaplan-Meier estimates and association with tooth loss using the χ2 test. Potentially significant predictive factors were investigated using univariate Cox regression. RESULTS: Tooth survival following RCT was 98% after 24 months; 88% after 48 months; 83% after 72 months; and 78% after 96 months. Four predictive factors were found to affect tooth loss as follows: preoperative pain (HR=3.2; p<0.001), teeth with less than two proximal contacts (HR=3.0; p=0.01), teeth with cores involving more than two surfaces (HR=2.0; p=0.03) and postoperative unscheduled dental attendances (UDA) (HR=2.7; p=0.01). CONCLUSIONS: Within the limitations of this study, the presence of preoperative pain; teeth with less than two proximal contacts or with cores involving more than two tooth surfaces; and occurrence of postoperative UDA were found to significantly increase the hazard of tooth loss.

A biomineral-inspired approach of synthesizing colloidal persistent phosphors as a multicolor, intravital light source.

Many in vivo biological techniques, such as fluorescence imaging, photodynamic therapy, and optogenetics, require light delivery into biological tissues. The limited tissue penetration of visible light discourages the use of external light sources and calls for the development of light sources that can be delivered in vivo. A promising material for internal light delivery is persistent phosphors; however, there is a scarcity of materials with strong persistent luminescence of visible light in a stable colloid to facilitate systemic delivery in vivo. Here, we used a bioinspired demineralization (BID) strategy to synthesize stable colloidal solutions of solid-state phosphors in the range of 470 to 650 nm and diameters down to 20 nm. The exceptional brightness of BID-produced colloids enables their utility as multicolor luminescent tags in vivo with favorable biocompatibility. Because of their stable dispersion in water, BID-produced nanophosphors can be delivered systemically, acting as an intravascular colloidal light source to internally excite genetically encoded fluorescent reporters within the mouse brain.

Detecting child sexual abuse images: Traits of child sexual exploitation hosting and displaying websites.

BACKGROUND: Automated detection of child sexual abuse images (CSAI) often relies on image attributes, such as hash values. However, electronic service providers and others without access to hash value databases are limited in their ability to detect CSAI. Additionally, the increasing amount of CSA content being distributed means that a large percentage of images are not yet cataloged in hash value databases. Therefore, additional detection criteria need to be determined to improve identification of non-hashed CSAI. OBJECTIVE: We aim to identify patterns in the locations and folder/file naming practices of websites hosting and displaying CSAI, to use as additional detection criteria for non-hashed CSAI. METHODS: Using a custom-designed web crawler and snowball sampling, we analyzed the locations and naming practices of 103 Surface Web websites hosting and/or displaying 8108 known CSAI hash values. RESULTS: Websites specialize in either hosting or displaying CSAI with only 20% doing both. Neither hosting nor displaying websites fear repercussions. Over 27% of CSAI were displayed in the home directory (i.e., main page) with only 6% located in at least 4th-level sub-folder. Websites focused more on organizing images than hiding them with 68% of hosted and 54% of displayed CSAI being found in folders formatted year/month. Qualitatively, hosting websites were likely to use alphanumeric or disguised folder and file names to conceal images, while displaying websites were more explicit. CONCLUSION: File and folder naming patterns can be combined with existing criteria to improve automated detection of websites and website locations likely hosting and/or displaying CSAI.

Expression of IL-20 Receptor Subunit ß Is Linked to EAE Neuropathology and CNS Neuroinflammation.

Considerable clinical evidence supports that increased blood-brain barrier (BBB) permeability is linked to immune extravasation of CNS parenchyma during neuroinflammation. Although BBB permeability and immune extravasation are known to be provoked by vascular endothelial growth factor-A (i.e., VEGF-A) and C-X-C motif chemokine ligand 12 (CXCL12), respectively, the mechanisms that link both processes are still elusive. The interleukin-20 (i.e., IL-20) cytokine signaling pathway was previously implicated in VEGF-mediated angiogenesis and is known to induce cellular response by way of signaling through IL-20 receptor subunit ß (i.e., IL-20RB). Dysregulated IL-20 signaling is implicated in many inflammatory pathologies, but it's contribution to neuroinflammation has yet to be reported. We hypothesize that the IL-20 cytokine, and the IL cytokine subfamily more broadly, play a key role in CNS neuroinflammation by signaling through IL-20RB, induce VEGF activity, and enhance both BBB-permeability and CXCL12-mediated immune extravasation. To address this hypothesis, we actively immunized IL-20RB-/- mice and wild-type mice to induce experimental autoimmune encephalomyelitis (EAE) and found that IL-20RB-/- mice showed amelioration of disease progression compared to wild-type mice. Similarly, we passively immunized IL-20RB-/- mice and wild-type mice with myelin-reactive Th1 cells from either IL-20RB-/- and wild-type genotype. Host IL-20RB-/- mice showed lesser disease progression than wild-type mice, regardless of the myelin-reactive Th1 cells genotype. Using multianalyte bead-based immunoassay and ELISA, we found distinctive changes in levels of pro-inflammatory cytokines between IL-20RB-/- mice and wild-type mice at peak of EAE. We also found detectable levels of all cytokines of the IL-20 subfamily within CNS tissues and specific alteration to IL-20 subfamily cytokines IL-19, IL-20, and IL-24, expression levels. Immunolabeling of CNS region-specific microvessels confirmed IL-20RB protein at the spinal cord microvasculature and upregulation during EAE. Microvessels isolated from macaques CNS tissues also expressed IL-20RB. Moreover, we identified the expression of all IL-20 receptor subunits: IL-22 receptor subunit α-1 (IL-22RA1), IL-20RB, and IL-20 receptor subunit α (IL-20RA) in human CNS microvessels. Notably, human cerebral microvasculature endothelial cells (HCMEC/D3) treated with IL-1ß showed augmented expression of the IL-20 receptor. Lastly, IL-20-treated HCMEC/D3 showed alterations on CXCL12 apicobasal polarity consistent with a neuroinflammatory status. This evidence suggests that IL-20 subfamily cytokines may signal at the BBB via IL-20RB, triggering neuroinflammation.

Neutron diffraction study of the monoclinic - tetragonal phase transition in NdNbO4 and NdTaO4.

Phase transition and high-temperature properties of NdNbO4 and NdTaO4 were studied in situ using powder neutron diffraction methods. Both oxides undergo a reversible phase transition from a monoclinic I2/a phase at low temperatures to a tetragonal I41/a phase at high temperatures. The phase transition has been investigated through analysis of the spontaneous strains and symmetry distortion modes. Well below the transition temperature, Tc, the thermal evolution of the lattice parameters and symmetry modes suggest the transition is continuous, although a small discontinuity in both the spontaneous strains and symmetry distortion modes shows the transition is strictly first order. Analysis of the refined structures reveals that the Nb and Ta cations are best described as having a distorted 6-coordinate arrangement in the monoclinic structure, with four short and two long bonds. Breaking of the two long bonds at high temperatures, resulting in a transformation of the Nb(Ta) coordination to a regular tetrahedron, is believed to be responsible for the first order nature of the transition.

Ultrabright plasmonic fluor nanolabel-enabled detection of a urinary ER stress biomarker in autosomal dominant tubulointerstitial kidney disease.

Autosomal dominant tubulointerstitial kidney disease (ADTKD)-uromodulin (UMOD) is the most common nonpolycystic genetic kidney disease, but it remains unrecognized due to its clinical heterogeneity and lack of screening test. Moreover, the fact that the clinical feature is a poor predictor of disease outcome further highlights the need for the development of mechanistic biomarkers in ADTKD. However, low abundant urinary proteins secreted by thick ascending limb cells, where UMOD is synthesized, have posed a challenge for the detection of biomarkers in ADTKD-UMOD. In the CRISPR/Cas9-generated murine model and patients with ADTKD-UMOD, we found that immunoglobulin heavy chain-binding protein (BiP), an endoplasmic reticulum chaperone, was exclusively upregulated by mutant UMOD in the thick ascending limb and easily detected by Western blot analysis in the urine at an early stage of disease. However, even the most sensitive ELISA failed to detect urinary BiP in affected individuals. We therefore developed an ultrasensitive, plasmon-enhanced fluorescence-linked immunosorbent assay (p-FLISA) to quantify urinary BiP concentration by harnessing the newly invented ultrabright fluorescent nanoconstruct, termed "plasmonic Fluor." p-FLISA demonstrated that urinary BiP excretion was significantly elevated in patients with ADTKD-UMOD compared with unaffected controls, which may have potential utility in risk stratification, disease activity monitoring, disease progression prediction, and guidance of endoplasmic reticulum-targeted therapies in ADTKD.NEW & NOTEWORTHY Autosomal dominant tubulointerstitial kidney disease (ADTKD)-uromodulin (UMOD) is an underdiagnosed cause of chronic kidney disease (CKD). Lack of ultrasensitive bioanalytical tools has hindered the discovery of low abundant urinary biomarkers in ADTKD. Here, we developed an ultrasensitive plasmon-enhanced fluorescence-linked immunosorbent assay (p-FLISA). p-FLISA demonstrated that secreted immunoglobulin heavy chain-binding protein is an early urinary endoplasmic reticulum stress biomarker in ADTKD-UMOD, which will be valuable in monitoring disease progression and the treatment response in ADTKD.

Insights into the structural variations in SmNb1-xTaxO4 and HoNb1-xTaxO4 combined experimental and computational studies.

The impact of Ta doping on two orthoniobates SmNbO4 and HoNbO4 has been studied using a combination of high-resolution powder diffraction and Density-Functional Theory calculations. In both ANb1-xTaxO4 (A = Sm, Ho) series the unit cell volume decreases as the Ta content increased demonstrating that the effective ionic radii of Ta is smaller than that of Nb in this structure. The average Sm-O distance and volume of the SmO8 polyhedra were invariant of the Ta content across the SmNb1-xTaxO4 solid solution whereas the average M-O (M = Nb or Ta) distance and MO6 polyhedral volume decrease with Ta doping. The analogous Ho oxides HoNb1-xTaxO4 do not form a complete solid solution when the samples were prepared at 1400 °C, rather there is a miscibility gap around x = 0.95, with HoTaO4 exhibiting the M'-type P2/c structure rather than the M-type I2/a structure of HoNbO4. Increasing the synthesis temperature to 1450 °C eliminates the miscibility gap. The energy difference between the P2/c and I2/a structures of HoTaO4 is found to be nearly 30 meV per f.u. with the total energy of the P2/c phase of HoTaO4 being more negative. First-principles calculations, carried out using Density-Functional Theory, reveal significant covalent character in the Nb-O bonds, which is reduced in the corresponding tantalates. Anisotropy in the Born Effective Charge tensors demonstrates the impact of the long M-O bond identified in the structural studies showing that the Nb and Ta cations are effectively six-coordinate. The similarity in the frequency of the intense Raman peak near 800 cm-1 due to the symmetric stretching of the Ta-O bonds is consistent with the description of that both polymorphs of HoTaO4 contain TaO6 octahedra.

Effect of Long- and Short-Range Disorder on the Oxygen Ionic Conductivity of Tm2(Ti2-xTmx)O7-x/2 "Stuffed" Pyrochlores.

The long-range average and short-range local structures in the Tm2(Ti2-xTmx)O7-x/2 (x = 0.00-0.67) series were studied using a combination of diffraction and spectroscopic techniques. The long-range average structure, established from synchrotron X-ray and neutron powder diffraction data, shows the development of multiphase regions from x = 0.134 and the formation of antisite cation disorder from x = 0.402. The crystal field splitting of the Ti4+ ions, as derived from the Ti L3-edge X-ray absorption near-edge structure (XANES) spectroscopy, decreases gradually from 2.17 to 1.92 eV with increasing Tm3+ content (x), reflecting the increase in coordination number from 6 to predominantly 7. This is consistent with a gradual evolution of the short-range local disorder from x = 0.00 to 0.67. These results suggest that local disorder develops gradually throughout the entire composition range, whereas changes in the long-range disorder occur more suddenly. Electrochemical impedance spectroscopic results show an increase in oxygen ionic conductivity at 1000 °C, by a factor of 4 upon doping at x = 0.268. This suggests that inducing small amounts of disorder into the pyrochlore structure, by stuffing, may lead to applications of this material as a solid electrolyte in solid-oxide fuel cells.