Smaller Unit Cell Volume Research Articles

Unraveling the pathological biomineralization of monosodium urate crystals in gout patients

Crystallization of monosodium urate monohydrate (MSU) leads to painful gouty arthritis. Despite extensive research it is still unknown how this pathological biomineralization occurs, which hampers its prevention. Here we show how inflammatory MSU crystals form after a non-inflammatory amorphous precursor (AMSU) that nucleates heterogeneously on collagen fibrils from damaged articular cartilage of gout patients. This non-classical crystallization route imprints a nanogranular structure to biogenic acicular MSU crystals, which have smaller unit cell volume, lower microstrain, and higher crystallinity than synthetic MSU. These distinctive biosignatures are consistent with the template-promoted crystallization of biotic MSU crystals after AMSU at low supersaturation, and their slow growth over long periods of time (possibly years) in hyperuricemic gout patients. Our results help to better understand gout pathophysiology, underline the role of cartilage damage in promoting MSU crystallization, and suggest that there is a time-window to treat potential gouty patients before a critical amount of MSU has slowly formed as to trigger a gout flare.

Redox Chemistries for Vacancy Modulation in Plasmonic Copper Phosphide Nanocrystals.

Copper phosphide (Cu3-xP) nanocrystals are promising materials for nanoplasmonics due to their substoichiometric composition, enabling the generation and stabilization of excess delocalized holes and leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present three Cu-coupled redox chemistries that allow postsynthetic modulation of the delocalized hole concentrations and corresponding LSPR absorption in colloidal Cu3-xP nanocrystals. Changes in the structural, optical, and compositional properties are evaluated by powder X-ray diffraction, electronic absorption spectroscopy, 31P magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, and elemental analysis. The redox chemistries presented herein can be used to access nanocrystals with LSPR energies of 660-890 meV, a larger range than has been possible through synthetic tuning alone. In addition to utilizing previously reported redox chemistries used for copper chalcogenide nanocrystals, we show that the largest structural and LSPR modulation is achieved using a divalent metal halide and trioctylphosphine. Specifically, nanocrystals treated with zinc iodide and trioctylphosphine have the smallest unit-cell volume (295.2 Å3) reported for P63cm Cu3-xP, indicating more Cu vacancies than have been previously observed. Overall, these redox chemistries present valuable insight into controlling the optical and structural properties of Cu3-xP.

The Synthesis and Crystal Structure of Six Quaternary Lithium-Alkaline Earth Metal Alumo-Silicides and Alumo-Germanides, A2LiAlTt2 (A = Mg, Ca, Sr, Ba; Tt = Si, Ge)

Reported are the synthesis and structural characterization of a series of quaternary lithium-alkaline earth metal alumo-silicides and alumo-germanides with the base formula A2LiAlTt2 (A = Ca, Sr, Ba; Tt = Si, Ge). To synthesize each compound, a mixture of the elements with the desired stoichiometric ratio was loaded into a niobium tube, arc welded shut, enclosed in a silica tube under vacuum, and heated in a tube furnace. Each sample was analyzed by powder and single-crystal X-ray diffraction, and the crystal structure of each compound was confirmed and refined from single-crystal X-ray diffraction data. The structures, despite the identical chemical formulae, are different, largely dependent on the nature of the alkaline earth metal. The differing cation determines the structure type—the calcium compounds are part of the TiNiSi family with the Pnma space group, the strontium compounds are isostructural with Na2LiAlP2 with the Cmce space group, and the barium compounds crystallize with the PbFCl structure type in the P4/nmm space group. The anion (silicon or germanium) only impacts the size of the unit cell, with the silicides having smaller unit cell volumes than the germanides.

Columbite supergroup of minerals: nomenclature and classification

AbstractThe columbite supergroup is established. It includes five mineral groups (ixiolite, wolframite, samarskite, columbite and wodginite) and one ungrouped species (lithiotantite). The criteria for a mineral to belong to the columbite supergroup are: the general stoichiometry MO2; the crystal structure based on the hexagonal close packing (hcp) of anions (or close to it); the six-fold coordination number of M-type cations (augmented to eight-fold in the case of slight distortion of hcp); and the presence of zig-zag chains of edge-sharing M-centred polyhedra. The ixiolite-type structure is considered as an aristotype with the space group Pbcn, the smallest unit cell volume, and the basic vectors a0, b0 and c0. Based on the multiplying of the ixiolite-type unit cell the following derivatives are distinguished: ixiolite type [ixiolite-group minerals; a = a0,b = b0 and c = c0; space group Pbcn; the members are ixiolite-(Mn2+), ixiolite-(Fe2+), scrutinyite, seifertite and srilankite]; wolframite type [wolframite-group minerals, ordered analogues of the ixiolite type with a = a0,b = b0 and c = c0; P2/c; the members are ferberite, hübnerite, huanzalaite, sanmartinite, heftetjernite, nioboheftetjernite, rossovskyite and riesite]; samarskite type [samarskite-group minerals; a = 2a0, b = b0 and c = c0; P2/c; the members are samarskite-(Y), ekebergite and shakhdaraite-(Y)]; columbite type [columbite-group minerals; a = 3a0,b = b0 and c = c0; Pbcn; the members are columbite-(Fe), columbite-(Mn), columbite-(Mg), tantalite-(Fe), tantalite-(Mn), tantalite-(Mg), fersmite, euxenite-(Y), tanteuxenite-(Y) and uranopolycrase]; and wodginite type [wodginite-group minerals; a = 2a0,b = 2b0 and c = c0; C2/c; the members are wodginite, ferrowodginite, titanowodginite, ferrotitanowodginite, tantalowodginite, lithiowodginite and achalaite]. Samarskite-(Yb), ishikawaite and calciosamarskite are insufficiently studied, tentatively considered as possible members of the samarskite supergroup. Qitianlingite, yttrocolumbite-(Y), yttrotantalite-(Y) and yttrocrasite-(Y) are questionable and need further studies. Polycrase-(Y) is discredited as identical to euxenite-(Y). Ixiolite has been renamed as ixiolite-(Mn2+), with the end-member formula (Ta2/3Mn2+1/3)O2. Ta- and Nb-dominant analogues of ixiolite with different schemes of charge balancing have the end-member formulae (M15+0.5M23+0.5)O2, M15+2/3M22+1/3)O2, M15+0.75M2+0.25)O2 or M15+0.8□0.2)O2 and the root name ‘ixiolite’ (for M1 = Ta) or ‘nioboixiolite’ (for M1 = Nb).

The Calcium Looping process for energy storage: Insights from in situ XRD analysis

This work reports a novel in situ XRD analysis on the multicycle calcination/carbonation of natural limestone and dolomite at relevant conditions for thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. The experiments allow analysing noninvasively the time evolution of the different phases involved in the Calcium Looping (CaL) process. Our work has revealed new key features to understand the progressive loss of multicyclic carbonation reactivity of the CaO derived from calcination. The CaCO3 structure formed in the first step of dolomite decomposition has smaller unit cell volume than the CaCO3 naturally present in limestone. The CaO that stems from decomposition of the CaCO3 derived from dolomite first decomposition shows a greater carbonation reactivity compared to the CaO derived from limestone. The smaller size of the CaO nascent crystals and their relatively higher reactivity for dolomite compared to limestone is related to the presence of inert MgO crystals, which prevent CaO sintering and crystallite growth. However, the size of the MgO crystals derived from dolomite decomposition increases monotonically with time, which progressively hampers their hindrance effect. Our work also shows a positive correlation between the growth of the CaO crystallite size and the decline of preferred orientation in the CaO (100) plane as the number of cycles is increased and CaO loses reactivity. The observed evolution with the cycles of CaO crystallite size and reactivity can be attributed to the incompletion of carbonation. The unreacted CaO that remains in the calcination step suffers severe sintering which hinders its reactivity. Thus, the fraction of fresh, reactive CaO derived from CaCO3 decomposition that nucleates on the old and less reactive CaO declines progressively with the cycles.

Phase Transitions in the "Spinel-Layered" Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) Cathodes upon (De)lithiation Studied with Operando Synchrotron X-ray Powder Diffraction.

“Spinel-layered” Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) materials are considered as a cobalt-free alternative to currently used positive electrode (cathode) materials for Li-ion batteries. In this work, their electrochemical properties and corresponding phase transitions were studied by means of synchrotron X-ray powder diffraction (SXPD) in operando regime. Within the potential limit of 2.2–4.9 V vs. Li/Li+ LiNi0.5Mn1.5O4 with cubic spinel type structure demonstrates the capacity of 230 mAh·g−1 associated with three first-order phase transitions with significant total volume change of 8.1%. The Li2Ni0.5Mn1.5O4 material exhibits similar capacity value and subsequence of the phase transitions of the spinel phase, although the fraction of the spinel-type phase in this material does not exceed 30 wt.%. The main component of Li2Ni0.5Mn1.5O4 is Li-rich layered oxide Li(Li0.28Mn0.64Ni0.08)O2, which provides nearly half of the capacity with very small unit cell volume change of 0.7%. Lower mechanical stress associated with Li (de)intercalation provides better cycling stability of the spinel-layered complex materials and makes them more perspective for practical applications compared to the single-phase LiNi0.5Mn1.5O4 high-voltage cathode material.

Creating, probing and confirming tetragonality in bulk FeNi alloys

Effects derived from the simultaneous application of passive, uniform saturating magnetic field and tensile stress during long-time annealing utilizing a unique and simple processing tool, the MultiDriver furnace, are reported. In particular, the evolution of the crystalline structure and the magnetic domain configuration of severely deformed and subsequently annealed equiatomic FeNi alloys were revealed by high-energy synchrotron X-Ray diffraction and Magneto-Optic Kerr Microscopy. These alloys are known to undergo a first-order magnetic phase transformation to a chemically ordered tetragonal (L10) structure in astronomical timeframes. MultiDriver-annealed specimens are found to retain a tetragonal crystallographic state and texture that is similar to that of the precursor deformed state, with a smaller unit cell volume and a larger c/a ratio relative to those of control samples that were annealed under the same conditions but without magnetic field and stress drivers. Magnetic domain images echo these observations: while as-cast FeNi alloys exhibit domain patterns consistent with the presence of a stress-modified cubic magnetocrystalline anisotropy, large areas of domains with uniaxial anisotropy are present in MultiDriver-annealed samples. While no chemical order was demonstrated in these samples, a strategy is proposed for achieving the ordered state by employing a passive magnetic gradient in the MultiDriver furnace to enhance diffusion.

Estimating the in-operando stabilities of AlFe2B2-Based compounds for magnetic refrigeration

The in-operando stabilities of AlFe2B2-based (aka, 1-2-2) compounds were investigated by mimicking two separate operating conditions (immersion in a heat transfer fluid and magnetic field cycling) of an active magnetic regenerator (AMR) refrigerator. Parent AlFe2B2 and Ga-containing samples of nominal composition Al1.2-xGaxFe2B2 (x = 0, 0.05 and 0.1) were prepared by casting and subsequent annealing. The chemical stability of pulverized (Al,Ga)Fe2B2-based compounds subjected to water immersion at room temperature for up to 960 h was evaluated. In a separate test, the mechanical stability of dry (Al,Ga)Fe2B2 cast-disk-shaped samples was studied utilizing a device constructed to mimic the AMR field cycling process. The materials’ responses as a function of water-immersion time or of magnetic field cycles were assessed by probing the crystal structure, the microstructure, the magnetic characters and the magnetocaloric response as quantified by the magnetic entropy change ΔSmag. The water-immersed pulverized samples exhibit exponential-decay-like degradations in magnetization and in ΔSmag. The Ga-containing compound exhibits significantly smaller reductions in magnetization and in ΔSmag after 960 h of water immersion relative to those of the Ga-free composition. In the separate magnetic-field-cycling test conducted under a dry condition, the structural and the magnetocaloric responses of both the Ga-free and Ga-containing disks remain similar after ∼5 × 105 cycles in and out of a 0.5 T magnetic field. The decrease in the magnetocaloric response during water immersion is attributed to the formation of oxide and/or hydroxide phases that reduced the AlFe2B2 phase fraction. The stable structure and the constant magnetocaloric response observed after magnetic field cycling are attributed to the extremely small unit cell volume change of AlFe2B2 through its magnetic phase transition. Overall, these results demonstrate that the AlFe2B2-based compounds exhibit good chemical stability upon water immersion that is improved by small Ga additions, and robust mechanical integrity upon dry magnetic field cycling, suggesting that AlFe2B2-based compounds are promising as robust AMR magnetic refrigeration working materials.

Energetic Butterfly: Heat-Resistant Diaminodinitro trans-Bimane.

Due to a significant and prolific activity in the field of design and synthesis of new energetic molecules, it becomes increasingly difficult to introduce new explosophore structures with attractive properties. In this work, we synthesized a trans-bimane-based energetic material—3,7-diamino-2,6-dinitro-1H,5H-pyrazolo-[1,2-a]pyrazole-1,5-dione (4), the structure of which was comprehensively analyzed by a variety of advanced spectroscopic methods and by X-ray crystallo-graphy (with density of 1.845 g·cm−3 at 173 K). Although obtained crystals of 4 contained solvent molecules in their structure, state-of-the-art density functional theory (DFT) computational techniques allowed us to predict that solvent-free crystals of this explosive would preserve a similar tightly packed planar layered molecular arrangement, with the same number of molecules of 4 per unit cell, but with a smaller unit cell volume and therefore higher energy density. Explosive 4 was found to be heat resistant, with an onset decomposition temperature of 328.8 °C, and was calculated to exhibit velocity of detonation in a range of 6.88–7.14 km·s−1 and detonation pressure in the range of 19.14–22.04 GPa, using for comparison both HASEM and the EXPLO 5 software. Our results indicate that the trans-bimane explosophore could be a viable platform for the development of new thermostable energetic materials.

On the Origin of the Negative Thermal Expansion Behavior of YCu

Among the intermetallics and alloys, YCu is an unusual material because it displays negative thermal expansion without spin ordering. The mechanism behind this behavior that is caused by the structural phase transition of YCu has yet to be fully understood. To gain insight into this mechanism, we experimentally examined the crystal structure of the low-temperature phase of YCu and discuss the origin of the phase transition with the aid of thermodynamics calculations. The result shows that the high-temperature (cubic CsCl-type) to low-temperature (orthorhombic FeB-type) structural phase transition is driven by the rearrangement of three covalent bonds, namely, Y-Cu, Y-Y, and Cu-Cu, which compete for the bonding energy and phonon entropy. At low temperatures, the mixing of Y and Cu does not take place easily because of the weak attractive force between these atoms expected from the small negative mixing enthalpy. This causes all three interactions to take part in the bonding, and Y and Cu are segregated to form an FeB-type structure, which is stabilized by internal energy. At higher temperatures, Cu ions are bound loosely with Y ions due to the large Y-Cu distance (3.01 Å), which results in large vibration entropy and stabilizes a CsCl-type crystal structure. In addition, the CsCl-type structure is reinforced by the Y-Y interaction between next-nearest neighbors, resulting in a smaller unit cell volume. The crystal structure has the simple cubic framework of Y containing Cu ions bound loosely at the cavity sites. The calculated frequency of the Y-like phonon modes is much higher than that of the Cu-like modes, indicating the presence of Y-Y covalent interactions in the CsCl-type phase.

Semi-hard magnetic nanocomposites based on out-of-equilibrium Fe2+δNb and Fe2+δTa Laves phases

Melt-spun Fe100-xNbx and Fe100-xTax alloys consisting of a hexagonal (C14) Laves phase and an iron-based bcc phase were found to exhibit room-temperature coercivities up to 0.45 and 0.48 kOe, respectively. The non-equilibrium C14 structures in the melt-spun alloys are characterized by a smaller unit cell volume, a higher Curie temperature and, presumably, a greater concentration of Fe compared to the C14 structures in the alloys annealed at 1533 K. The room-temperature coercivity, which correlates with the C14 lattice contraction, is believed to be caused by the magnetocrystalline anisotropy of the non-equilibrium Laves phase with the latter being magnetically coupled with the Fe phase via an intergranular exchange interaction. On the other hand, a coercivity of around 0.3 kOe persists in the melt-spun alloys above the Curie temperature of the C14 phase. This high-temperature coercivity may originate from the shape or strain anisotropy of the Fe phase particles. The energy density of the reported two-phase alloys is not sufficiently high to consider them potential hard magnetic materials. However, the pure non-equilibrium Fe2+δNb and Fe2+δTa compounds may be of interest if they can be isolated and textured.

The mixed-valence Ce4Al2O10 aluminate

Reversible oxidation-reduction of cerium ions in a monoclinic Ce4Al2O9 aluminate was studied by XRD, TEM, temperature programmed reduction-oxidation and magnetic methods. It has been shown that nanocrystalline Ce4Al2O9 reacts with gaseous oxygen, undergoing at 20–300 °C transformation into a new, oxidized phase described in the same P21/c space group, but with 10% smaller unit cell volume. Magnetic measurements revealed that the oxidized Ce4Al2O9 still contains ~20% of paramagnetic Ce3+ ions. The oxidized Ce aluminate may be reduced back to Ce4Al2O9 by heating in H2 atmosphere to 1000 °C. The reversibility of the oxidation-reduction process of Ce4Al2O9 aluminate bears resemblance to the behaviour of fluorite type CeO2, and may be of interest for applications (e.g., in catalytic high-temperature oxidation reactions).

Synthesis of novel branched β-NaLuF4: Yb/Er upconversion luminescence material and investigation of its optical properties

Branched β-NaLuF4: Yb/Er was synthesized using a simple hydrothermal method by controlling the NaF/Ln molar ratio. In contrast to the β-NaYF4: Yb/Er hexagonal disks, the branched β-NaLuF4: Yb/Er has stronger emission intensity. The integrated intensities of green and red emission bands were as 6.2 and 3.3 times as that of NaYF4, respectively. The branched β-NaLuF4: Yb/Er has the smaller unit cell volume, the higher absorption intensity around 980 nm and the lower crystal field symmetry than NaYF4, which made a significant contribution to the stronger upconversion (UC) fluorescence emissions. The results indicate that the branched β-NaLuF4: Yb/Er is an excellent UC luminescence material. The current research has a great potential in improving near-infrared conversion efficiency of solar cells.

Synthesis, structure, and polymorphic transitions of praseodymium(iii) and neodymium(iii) borohydride, Pr(BH4)3 and Nd(BH4)3.

In this work, praseodymium(iii) borohydride, Pr(BH4)3, and an isotopically enriched analogue, Pr(11BD4)3, are prepared by a new route via a solvate complex, Pr(11BD4)3S(CH3)2. Nd(BH4)3 was synthesized using the same method and the structures, polymorphic transformations, and thermal stabilities of these compounds are investigated in detail. α-Pr(BH4)3 and α-Nd(BH4)3 are isostructural with cubic unit cells (Pa3[combining macron]) stable at room temperature (RT) and a unit cell volume per formula unit (V/Z) of 180.1 and 175.8 Å3, respectively. Heating α-Pr(BH4)3 to T ∼ 190 °C, p(Ar) = 1 bar, introduces a transition to a rhombohedral polymorph, r-Pr(BH4)3 (R3[combining macron]c) with a smaller unit cell volume and a denser structure, V/Z = 156.06 Å3. A similar transition was not observed for Nd(BH4)3. However, heat treatment of α-Pr(BH4)3, at T ∼ 190 °C, p(H2) = 40 bar and α-Nd(BH4)3, at T ∼ 270 °C, p(H2) = 98 bar facilitates reversible formation of another three cubic polymorph, denoted as β, β' and β''-RE(BH4)3 (Fm3[combining macron]c). Moreover, the transition β- to β'- to β''- is considered a rare example of stepwise negative thermal expansion. For Pr(BH4)3, ∼2/3 of the sample takes this route of transformation whereas in argon only ∼5 wt%, and the remaining transforms directly from α- to r-Pr(BH4)3. The β-polymorphs are porous with V/Z = 172.4 and 172.7 Å3 for β''-RE(BH4)3, RE = Pr or Nd, respectively, and are stabilized by the elevated hydrogen pressures. The polymorphic transitions occur due to rotation of RE(BH4)6 octahedra without breaking or forming chemical bonds. Structural DFT optimization reveals the decreasing stability of α-Pr(BH4)3 > β-Pr(BH4)3 > r-Pr(BH4)3.

Microscopic strain in a grossular-pyrope solution anti-correlates with excess volume through local Mg-Ca cation arrangement, more strongly at high Ca/Mg ratio

Unit-cell volume and microstrain of Py 40 Gr 60 garnets vary with synthesis temperature and annealing time, showing a strong negative correlation, as is also seen in another garnet solid solution, Py 20 Gr 80 . This anti-correlation is explained by local Ca-Mg cation arrangement in which Ca-Ca and Mg-Mg third-nearest-neighbor (Same 3NN = S3NN) pairs form at rates other than those expected from random Ca-Mg distribution. S3NN pairs cause microstrain (Bosenick et al. 2000) but allow more efficient packing than random Ca-Mg pairings that contribute to excess volume, hence smaller cell volumes correlate with more microstrain. Both longer annealing time and higher heating temperature cause more S3NN formation, larger microscopic strain, and smaller unit-cell volume. The anti-correlation of microstrain and excess volume is weaker in our previous study of pyrope-rich solutions (i.e., Py 80 Gr 20 , Du et al. 2016) because excess volume varies little from Ca-Ca S3NN pairings in pyrope-rich solutions, whereas Mg-Mg S3NN pairings in grossular-rich solutions studied here are effective at reducing excess volume. Heating to 600 °C under room pressure or cold hydrostatic compression to 10 GPa does not reset microstrain. Margules’ formulations for microstrain and volume as a function of Ca/Mg ratio captures these features, especially the two-peaked distribution of microstrain with composition discovered by Du et al. (2016). The similar two-peaked distributions of microstrain and excess energies derived from ab initio calculation with short-range ordering of Mg and Ca cations (Vinograd and Sluiter 2006) indicate that the macroscopic thermodynamic mixing properties of solid solutions are directly related to arrangement of cations with large size misfit. The observed changes of microstrain with annealing temperature suggest that mixing properties measured from our pyrope-grossular garnet solid solutions synthesized at same temperature can serve as better experimental constrains for computational work.

Highly conductive n-type NiCo2O4-δ epitaxial thin films grown by RF sputtering

NiCo2O4-δ (NCO) epitaxial thin films have been grown on MgAl2O4(001) substrates at different Ar/O2(1:1) pressure by RF sputtering technique. HRXRD study indicates best crystalline quality and smallest unit cell volume are obtained in NCO thin films deposited at 75Pa. Hall measurement reveals NCO thin films are of n-type conductivity with the electron mobility and electron density of NCO films in the range of 0.09–1.05cm2/Vs and 1.06–5.94×1021cm−3, respectively. Maximum conductivity of 178S/cm is obtained in NCO thin films deposited at 75Pa, which surpasses the conductivity of NCO films grown by using PLD method. XPS spectra confirm mixed valence states for nickel and cobalt ions, and existence of oxygen vacancies which triggers n-type conductivity. The deposition pressure dependent carrier density and unit cell volume are closely related to the concentration of oxygen vacancies.

Crystal structure and compositional analysis of epitaxial (K0.56Na0.44)NbO3films prepared by hydrothermal method

Abstract

Topotactic and reconstructive changes at high pressures and temperatures from Cs-natrolite to Cs-hexacelsian

Synchrotron X-ray powder diffraction experiments have been performed on dehydrated Cs- exchanged natrolite to systematically investigate successive transitions under high pressures and temperatures. At pressures above 0.5(1) GPa using H2O as a pressure-transmitting medium and after heating to 100 °C, dehydrated Cs16Al16Si24O80 (deh-Cs-NAT) transforms to a hydrated phase Cs16Al16Si24O80·16H2O (Cs-NAT-II), which has a ca. 13.9% larger unit-cell volume. Further compression and heating to 1.5 GPa and 145 °C results in the transformation of Cs-NAT-II to Cs16Al16Si32O96 (anh-Cs-POL), a H2O-free pollucite-like triclinic phase with a 15.6% smaller unit-cell volume per 80 framework oxygen atoms (80O f ). At pressures and temperatures of 3.7 GPa and 180 °C, a new phase Cs1.547Al1.548Si6.452O16 (Cs-HEX) with a hexacelsian framework forms, which has a ca. 1.8% smaller unit-cell volume per 80O f . This phase can be recovered after pressure release. The structure of the recovered Cs-HEX has been refined in space group P 63/ mcm with a = 5.3731(2) A and c = 16.6834(8) A, and also been confirmed by HAADF-STEM real space imaging. Similar to the hexacelsian feldspar (i.e., BaAl2Si2O8), Cs-HEX contains Cs+ cations that act as bridges between the upper and lower layers composed of tetrahedra and are hexa-coordinated to the upper and lower 6-membered ring windows. These pressure- and temperature-induced reactions from a zeolite to a feldspar-like material are important constraints for the design of materials for Cs+ immobilization in nuclear waste disposal.

Thermoelectric properties of hot-pressed Tl9LnTe6 (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb) and Tl10−xLaxTe6 (0.90 ⩽ x ⩽ 1.05)

In the first part of this work, thallium lanthanide tellurides with composition Tl9LnTe6 (Ln=La, Ce, Pr, Nd, Sm, Gd, Tb) have been prepared and their high temperature electrical and thermal transport properties investigated. Nearly single phase samples were obtained. Rietveld refinement results showed that Tl9CeTe6 had an exceptionally small unit cell volume of 1033Å3. The electrical conductivity and thermal conductivity increased across the lanthanide series from La to Tb. On the other hand, the Seebeck coefficient values decreased with Ln varying from La to Tb. Tl9SmTe6 or Tl9GdTe6 constituted an exception, as the Seebeck coefficient of Tl9SmTe6 was smaller than that of Tl9GdTe6. Tl9LaTe6 has the largest figure-of-merit of this series.Thereafter, Tl10−xLaxTe6 samples were prepared with x=0.90, 0.95, 1.00, 1.05, 1.10, aiming toward higher zT through composition optimization and expanding of the measurement temperature range. With the increasing La content, the unit cell volume increased, while the electrical conductivity, thermal conductivity and lattice thermal conductivity decreased, and the Seebeck coefficient increased. The highest zT=0.57 was observed for Tl9LaTe6 at 600K.

Quantification of -particle radiation damage in zircon

Analysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the a-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10 B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10 B + n → 7 Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7 Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7 Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29 Si NMR to be 252 ± 24 atoms for the 10 B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ∼6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as a function of a dose of 0.21 A 3 /10 18 α-events/g, which is significantly less than the increase of 3.55 A 3 /10 18 α-events/g seen in Pu-doped zircon and 2.18 A 3 /10 18 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil.