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Applied cutting-edge electronic structure and phonon simulations provide a reliable knowledge about the stability of perovskite structures and their electronic properties, which are crucial for des...

Superconductivity was first observed more than a century ago, but the search for new superconducting materials remains a challenge. The Cooper pairs in superconductors are ideal embodiments of quantum entanglement. Thus, novel superconductors can be critical for both learning about electronic systems in condensed matter and for possible application in future quantum technologies. Here two previously unreported materials, NbIr$_2$B$_2$ and TaIr$_2$B$_2$, are presented with superconducting transitions at 7.2 and 5.2 K, respectively. They display a unique noncentrosymmetric crystal structure, and for both compounds the magnetic field that destroys the superconductivity at 0 K exceeds one of the fundamental characteristics of conventional superconductors (the Pauli limit), suggesting that the superconductivity may be unconventional. Supporting this experimentally based deduction, first-principle calculations show a spin split Fermi surface due to the presence of strong spin-orbit coupling. These materials may thus provide an excellent platform for the study of non-BCS superconductivity in intermetallic compounds., 36 pages, 11 figures

The synthesis, structure and elementary magnetic characterization of the homometallic warwickite V2OBO3 are reported. The material adopts the orthorhombic warwickite structure type at room temperature, space group Pnma (No. 62) with lattice parameters a = 9.2317(1) A, b = 3.1172(1) A, and c = 9.5313(1) A. Temperature-dependent magnetic susceptibility, electrical resistivity, and specific heat measurements show anomalies near 35 K, between 135 K and 150 K, and near 260 K, with the transition at ~ 35 K likely to a ferrimagnetic state. High resolution synchrotron powder X-ray diffraction data at temperatures between 295 K and 90 K display significant peak splitting upon cooling, indicating that at least one crystallographic symmetry change occurs at low temperatures.

The crystal structure and elementary properties of La15NbxGe9 are reported. Single-crystal X-ray diffraction, from a crystallite with only 0.12 Nb/formula unit, reveals that this compound, although transition metal deficient, crystallizes in a hexagonal “15-1-9”-like structure type, space group P63mc (no. 186) with lattice parameters a = b = 15.5017(2) A, c = 6.9173(2) A. The physical properties were examined by specific heat and resistivity measurements. La15Nb0.4Ge9 shows metallic behavior, and no superconductivity is observed above 0.4 K. The Sommerfeld coefficient (γ = 62.41(8) mJ mol−1 K−2) and the Debye temperature ( θ D = 267(1) K) were estimated from a fit to the low temperature heat capacity data. La15Nb0.4Ge9 is the first reported compound in the ternary La-Nb-Ge system.

Metallization is one of the key process steps to fabricate solar cells with high performance in a cost-effective way. Majority of photovoltaic solar cell manufacturing uses thick film screen print metallization with Ag containing paste to produce solar cells. The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will become a problem in view of the continually increasing production of PV modules. These can be recycled for about the same cost as their disposal. The proposed method of acidic and basic etching of contacts, presented in this article can be successfully applied to broken solar cells from the landfill without a specialist analysis procedure. The amount of silver that can be recovered from the etching solution is up to 1.6 kg/t of broken solar cells. The step-by-step procedure improves efficiency of silver recovery. The best and easiest method for general verification of the silver etching rate is classic titration with suitable concentrations of titrant solution.

A combination of theoretical calculation and the experimental synthesis to explore the new ternary compound is demonstrated in the Sr–Pt–Bi system. Because Pt–Bi is considered as a new critical charge-transfer pair for superconductivity, it inspired us to investigate the Sr–Pt–Bi system. With a thorough calculation of all the known stable/metastable compounds in the Sr–Pt–Bi system and crystal structure predictions, the thermodynamic stability of hypothetical stoichiometry, SrPtBi2, is determined. Following the high-temperature synthesis and crystallographic analysis, the first ternary bismuthide in Sr–Pt–Bi, SrPtBi2 was prepared, and the stoichiometry was confirmed experimentally. SrPtBi2 crystallizes in the space group Pnma (S.G. 62, Pearson Symbol oP48), which matches well with theoretical prediction using an adaptive genetic algorithm. Using first-principles calculations, we demonstrate that the orthorhombic structure has lower formation energies than other 112 structure types, such as tetragonal BaMn...

A heterojunction with excellent visible light response and stability based on titanium dioxide nanotubes (TiO2 NTs), bismuth sulfide quantum dots (Bi2S3 QDs), and platinum nanoparticles (Pt NPs) is proposed. Both Pt NPs (3.0 ± 0.2 nm) and Bi2S3 QDs (3.50 ± 0.20 nm) are well distributed on the (i) top parts, (ii) inner walls, and (iii) outer walls of the TiO2 NTs. Visible-light-induced photoreaction was initialized by excitation of narrow band gap Bi2S3 QDs, followed by electron injection to the conduction band of TiO2, while Pt NPs acted as electron traps, enhacing O2–• generation. Phenol in the aqueous phase and toluene in the gas phase were efficiently degraded over Bi2S3–Pt NTs, even for wavelengths longer than 455 and 465 nm, respectively, while no degradation of model compounds was observed over pristine TiO2 NTs under the same irradiation conditions. Photocatalytic tests of phenol degradation in the presence of scavengers revealed that superoxide radicals were responsible for the visible-light degra...

In the present study we report a successful synthesis of the new intermetallic compound Nd2PtGe3 by an arc-melting method. The powder X-ray diffraction analysis indicates that this compound crystallizes in an disordered variant of the AlB2-type structure (space group P6/mmm, no. 191) with lattice parameters a = 4.2455 A and c = 4. 1933 A. The compound exhibits a cluster-glass transition below Tf = 2.9 K, characterized through ac and dc magnetic susceptibility and heat capacity measurements.

The crystallographic, electronic transport and thermal properties of Ca 2 PdGe 3 and Ca 2 PtGe 3 are reported. The compounds crystalize in an ordered variant of the AlB 2 crystal structure, in space group P 6/mmm , with the lattice parameters a = 8.4876(4) A/8.4503(5) A and c = 4.1911(3) A/4.2302(3) A for Ca 2 PdGe 3 and Ca 2 PtGe 3 , respectively. The resistivity data exhibit metallic behavior with residual-resistivity-ratios (RRR) of 13 for Ca 2 PdGe 3 and 6.5 for Ca 2 PtGe 3 . No superconducting transition is observed down to 0.4 K. Specific heat studies reveal similar values of the Debye temperatures and Sommerfeld coefficients: Θ D = 298 K, γ = 4.1 mJ mol − 1 K − 2 and Θ D = 305 K, γ = 3.2 mJ mol − 1 K − 2 for Ca 2 PdGe 3 and Ca 2 PtGe 3 , respectively. The low value of γ is in agreement with the electronic structure calculations.

La 3 Co and La 3 Ni are reported superconductors with transition temperatures of 4.5 and 6 K, respectively. Here, we reinvestigate the physical properties of these two intermetallic compounds with magnetic susceptibility χ, specific heat C p and electrical resistivity ρ measurements down to 1.9 K. Although bulk superconductivity is confirmed in La 3 Co, as observed previously, only a trace of it is found in La 3 Ni, indicating that the superconductivity in La 3 Ni originates from an impurity phase. Superconducting state parameters for La 3 Co, including lower and upper critical fields and the superconducting gap, are estimated. Results of the theoretical calculations of the electronic structure for both materials are also presented, and comparison of the Fermi level location in La 3 Co versus La 3 Ni explains its larger superconducting T c . A major discrepancy between band structure calculations and the experimentally measured Sommerfeld coefficient is found. The measured electronic density of states is about 2.5 times larger than the theoretical value for La 3 Co. This effect cannot be explained by the electron-phonon interaction alone. Renormalization of γ, as well as an ∼T 2 behavior of the resistivity, suggests the presence of spin fluctuations in both systems.

Single crystals of SrCo2Al and BaCo2Al9 were grown using a self-flux method. A LeBail analysis of the powder X-ray diffraction patterns show that both compounds crystallize in a hexagonal (P6/mmm) crystal structure with lattice parameters: a ​= ​7.8995(1) A, c ​= ​3.9159(1) A for SrCo2Al9, and a ​= ​7.9162(2) A, c ​= ​3.9702(1) A for BaCo2Al9 aluminide. The low temperature analysis of the heat capacity measurements give a Sommerfeld coefficient γ ​= ​4.99(6) mJ mol−1 K−2 for SrCo2Al9 and almost twice larger γ ​= ​7.94(9) mJ mol−1 K−2 for BaCo2Al9. Resistivity measurements show metallic-like behavior, with reasonably large residual resistivity ratio RRR ​= ​6 and 10 for SrCo2Al9 and BaCo2Al9, respectively. Neither heat capacity nor resistivity measurements reveal any phase transition down to 1.8 ​K.

The structure, optical and electrical properties of manganese borosilicate glasses of the composition xMnO–(80 − x)SiO2–20B2O3 (x = 40, 50, and 60 mol%) were investigated. The dependence of the glass structure on its composition was discussed and related to electrical properties. A separation of two amorphous phases was observed. It was suggested that one phase is MnO-rich and the other is SiO2-rich. It was found that the conductivity of MnO-rich phase is much higher than the conductivity of the other phase. The analysis of the valence states of manganese suggest that the transition metal ions are mainly present at second oxidation state. Magnetic susceptibility measurements show antiferromagnetic interactions in samples.

Single crystals of a new ternary aluminide ErV$_2$Al$_{20}$ were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV$_2$Al$_{20}$ is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment $\mu_{eff}$ = 9.27(1) $\mu_B$ and Curie-Weiss temperature $\Theta_{CW}$ = -0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatures that is attributed to the presence of a low-energy Einstein mode with characteristic temperature $\Theta_E$ = 44 K, approximately twice as high as in the isostructural 'Einstein solid' VAl$_{10.1}$., Comment: 15 pages, 9 figures + Supplementary Material; Accepted for publication in Journal of Solid State Chemistry

Composites of Nb-doped strontium titanate mixed with yttria-stabilized zirconia or cerium oxide in 50:50, 70:30 and 85:15 weight ratios were evaluated as possible anode/electrolyte interface materials for solid oxide fuel cells in terms of chemical compatibility, electrical conductivity and mechanical properties. It has been shown that composite samples prepared by typical powder-mixing methods remain single-phase up to 1400°C. The electrical conductivity of these composites, regardless of their composition and fabrication conditions, is lower than the conductivity of pure SrTi0.98Nb0.02O3–δ, but in most cases sufficient for solid oxide fuel cells anode application. The best properties are found for samples reduced at 1400°C for 10 h in H2 atmosphere. The observations made by scanning electron microscope suggest that the grains of both phases are well-distributed throughout the whole volume of the investigated samples, and that the composites with CeO2 better adhere to the electrolyte surface. The electrical results confirm that composites with at most 30 wt % of YSZ/CeO2 phase fulfill the anode requirements. However, the fuel cell performance tests indicate that the application of composite with CeO2 results in the lower power density than the application of the composite with YSZ.

Granular superconductors are composed of superconducting grains between a few and hundreds nanometres in size, embedded in an insulating, semiconducting or metallic matrix. Their properties are very interesting thanks to the presence of Coulomb effects, electron tunnelling and Josephson coupling between granules. The presence of a magnetic field may cause either a decrease or increase in the material's resistivity. In this paper the electrical properties of (Bi,Pb)–Sr–Ca–Cu–O granular superconductors obtained by the solid state crystallization method were studied. The granules were in the range from 10 nm to 30 nm. All the studied materials below the transition temperature contained granules in the superconducting state. They showed positive magnetoresistance. The hopping conductivity model with the exponential temperature dependence of resistivity was applied. The obtained values of the exponents were lower than those typical for granular systems, but they increased with an increase in the magnetic field.

Electrical properties of (Bi, Pb)4Sr3Ca3Cu4Ox granular metals and superconductors obtained by the solid state crystallization method were studied. The studied materials may be considered as 3D systems of small oval granules of the (Bi, Pb)2Sr2CuOx and (Bi, Pb)2Sr2CaCu2Ox phases embedded in the insulating matrix. They may by divided into two main groups: these in which the granules below the critical temperature transform into the superconducting state and those in which they remain in the normal state throughout the entire temperature range studied. The electronic transport in the (Bi, Pb)Sr–Ca–Cu–O granular system of the granules in the normal state occurs by the variable range hopping mechanism either with or without Coulomb interactions. The materials, which below the transition temperature contain the granules in the superconducting state, show different types of temperature dependence of resistivity. Those composed of very small granules (10 nm) of the superconducting phase exhibit an exponential dependence typical of the strong localization regime. In samples containing relatively large granules of the 2 2 0 1 phase (30 nm), the bulk superconducting state was achieved. The intermediate materials show unusual temperature dependence of resistivity, not compatible with the known models of electronic transport in granular materials.

The double perovskites La2CoVO6, La2CoTiO6, and La2NiVO6, are described. Rietveld fitting of neutron and powder X-ray diffraction data show La2NiVO6 and La2CoVO6 to have a disordered arrangement of B-cations whereas La2CoTiO6 shows ordering of the B-cations (with ∼5% Co/Ti inversion). Curie–Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3 K for La2CoVO6, La2CoTiO6, and La2NiVO6, respectively, and magnetic transitions are observed. La2CoTiO6 prepared by our method differs from material prepared by lower-temperature routes. A simple antiferromagnetic spin model is consistent with the data for La2CoTiO6. These compounds are semiconductors with bandgaps of 0.41 (La2CoVO6), 1.02 (La2CoTiO6) and 0.45 eV (La2NiVO6).

Polycrystalline ${\mathrm{Hf}\phantom{\rule{1.0pt}{0ex}}\mathrm{Pd}}_{2}\mathrm{Al}$ has been synthesized using the arc-melting method and studied under ambient-pressure conditions by x-ray diffraction from room temperature up to 450 \ifmmode^\circ\else\textdegree\fi{}C. High-pressure x-ray diffraction up to 23 GPa was also performed using Diacell-type membrane diamond anvil cells. The estimated linear thermal expansion coefficient was found to be $\ensuremath{\alpha}=1.40(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, and the bulk modulus derived from the fit to the third-order Birch-Murnaghan equation of state is ${B}_{0}=97(2)$ GPa. Resistivity studies under applied pressure $(p\ensuremath{\le}7.49\phantom{\rule{0.16em}{0ex}}\mathrm{GPa})$ showed a linear decrease of superconducting critical temperature with increasing pressure and the slope $d{T}_{c}/dp=\ensuremath{-}0.13(1)\phantom{\rule{0.16em}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}{\mathrm{GPa}}^{\ensuremath{-}1}$. The same behavior is observed for the electron-phonon coupling constant ${\ensuremath{\lambda}}_{\mathrm{ep}}(p)$ that changes from 0.67 to 0.6, estimated for $p=0.05$ and 7.49 GPa, respectively. First-principles electronic structure and phonon calculation results are presented and used to estimate the magnitude of electron-phonon interaction ${\ensuremath{\lambda}}_{\mathrm{ep}}$ and its evolution with pressure. Theoretical results explain the experimentally observed decrease in ${T}_{c}$ due to considerable lattice stiffening.

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P63/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn2Ru4O11 is reported.

We present results of the electrical resistivity of a Nd1.84Ce0.16CuO4−y superconducting (Tc=22.4 K) single crystal in magnetic fields up to 13 T. The measurements were performed by the van der Pauw method in both possible configurations of the electrodes. In one of the configurations a resistivity peak has been observed close to the critical temperature, whereas the peak was not visible for the other configuration. We propose a simple model assuming an inhomogeneous distribution of cerium, which may explain this effect. Results of AC-susceptibility measurements on the crystal and its fragments support this model.

The layered, noncentrosymmetric heavy element ${\text{PbTaSe}}_{2}$ is found to be superconducting. We report its electronic properties accompanied by electronic-structure calculations. Specific heat, electrical resistivity, and magnetic-susceptibility measurements indicate that PbTaSe${}_{2}$ is a moderately coupled, type-II BCS superconductor (${T}_{c}=3.72$ K, Ginzburg--Landau parameter $\ensuremath{\kappa}=17$) with an electron-phonon coupling constant of ${\ensuremath{\lambda}}_{ep}=0.74$. Electronic-structure calculations reveal a single bulk three-dimensional Dirac cone at the $K$ point of the Brillouin zone derived exclusively from its hexagonal Pb layer; it is similar to the feature found in graphene except there is a 0.8 eV gap opened by spin-orbit coupling. The combination of large spin-orbit coupling and lack of inversion symmetry also results in large Rashba splitting on the order of tenths of an eV.

We report properties of Nd 2-x Ce x CuO 4-y (NCCO) single crystals which were reduced using special reduction technique, described previously by Brinkmann et al. The superconducting phase diagram obtained for our Nd 2-x Ce x CuO 4-y single crystals is the first sign showing the existence of superconductivity beyond the region 0.13

The influence of post-growth treatment, consisting of high-temperature reduction, quench and oxidation, on the structural, electrical and magnetic properties of PrBa 2 Cu 3 O 7− δ single crystals, obtained in Al 2 O 3 and ZrO 2 crucibles by the self-flux method, was examined. We report on the observation of inhomogeneous superconductivity in several Al-doped crystals from the ac magnetic susceptibility and resistivity measurements. Superconducting crystals were characterised by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Room-temperature scanning tunnelling microscopy (STM) was used to study the topography and local electric conductivity of the crystal surface after thermal treatment. We attribute the onset of the superconductivity in our samples to the structural changes after high-temperature reduction in argon atmosphere providing the decrease in number of Pr on Ba site defects and enhanced by the existence of Al-rich clusters in the material.

We report the observation of superconductivity in the CuIr${}_{2}$Se${}_{4}$ spinel induced by partial substitution of Pt for Ir. The optimal doping level for superconductivity in Cu(Ir${}_{1\ensuremath{-}x}$Pt${}_{x}$)${}_{2}$Se${}_{4}$ is $x$ $=$ 0.2, where ${T}_{c}$ is 1.76 K. A superconducting ${T}_{c}$ vs composition dome is established between the metallic, normal conductor CuIr${}_{2}$Se${}_{4}$ and semiconducting CuIrPtSe${}_{4}$. Electronic structure calculations show that the optimal ${T}_{c}$ occurs near the electron count of a large peak in the calculated electronic density of states and that CuIrPtSe${}_{4}$ is a band-filled insulator. Characterization of the superconducting state in this heavy metal spinel through determination of $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{c}$ indicates that it is BCS-like. The relatively high upper critical field at the optimal superconducting composition [${H}_{c}$${}_{2}$(0) $=$ 3.2 T] is much larger than that reported for analogous rhodium spinels and is comparable to or exceeds the Pauli field (${\ensuremath{\mu}}_{0}{H}_{P}$), suggesting that strong spin-orbit coupling may influence the superconducting state. Further, comparison to doped CuIr${}_{2}$S${}_{4}$ suggests that superconductivity in iridium spinels is not necessarily associated with the destabilization of a charge-ordered spin-paired state through doping.

We have used a suite of diffraction, thermodynamic, and transport measurements to study the localized rattling of Al guest atoms in VAl${}_{10.1}$. The mean-square displacement of the rattling atom shows a concave-down temperature dependence. This is characteristic of an anharmonic vibration, the frequency of which increases with amplitude, akin to a particle in a box. We find that the rattling is best described in terms of a sixth-order interatomic potential, with negligible contributions from harmonic and quartic terms. The rattler has a characteristic temperature of ${\ensuremath{\theta}}_{RM}=21$ K and couples strongly to both the acoustic phonons and conduction electrons. The coupling to the phonons is evident from the large value of the Gr\"uneisen parameter, which increases with decreasing temperature to $\ensuremath{\Gamma}\ensuremath{\approx}43$ at 5 K. Below 6 K, the electrical resistivity varies as ${T}^{3}$, which can be explained in terms of electron scattering from damped sixth-order vibrations. VAl${}_{10.1}$ is a superconductor below ${T}_{c}=1.53$ K, with an upper critical field of $\ensuremath{\sim}$1 kG.

Several physical properties of the superconducting Heusler compounds, focusing on two systems (Y, Lu, Sc)Pd2Sn and APd2M, where A=Hf, Zr and M=Al, In, are summarized and compared. The analysis of the data shows the importance of the electron-phonon coupling for superconductivity in this family. We report the superconducting parameters of YPd2Sn, which has the highest Tc among all known Heusler superconductors., Comment: Accepted for publication in Phys. Rev. B

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a ?7-doublet ground state and a ?8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a ?6-excited state resides at 32 meV; however, the ?8/?6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Gruneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the ?7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

Superconductivity and structural characterization is reported for the Heusler structure compounds ${\text{ScRh}}_{2}\text{Sn}$, ${\text{LuRh}}_{2}\text{Sn}$, and ${\text{YRh}}_{2}\text{Sn}$. The superconducting ${T}_{\text{c}}$'s are 2.0 K, 2.9 K, and 4.1 K, respectively. The electronic contributions to the specific heat and the Debye temperatures are reported, and suggest that the observed trend in ${T}_{\text{c}}$ is governed primarily by an increase in electron-phonon coupling on going from ${\text{ScRh}}_{2}\text{Sn}$ to ${\text{YRh}}_{2}\text{Sn}$. The electron-phonon coupling constant ${\ensuremath{\lambda}}_{\text{ep}}$ and the normalized specific-heat jump $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{\text{c}}$ suggest that the $M{\text{Rh}}_{2}\text{Sn}$ system evolves from weak coupling to moderate coupling superconductivity.

We have searched for time-reversal symmetry-breaking fields in the noncentrosymmetric superconductor ${\text{Mg}}_{10}{\text{Ir}}_{19}{\text{B}}_{16}$ via muon spin relaxation $(\ensuremath{\mu}\text{SR})$ in zero applied field. We also measured the temperature dependence of the superfluid density by muon spin rotation in transverse field to investigate the superconducting pairing symmetry in two polycrystalline samples of significantly different purities. In the high-purity sample, we detected no time-reversal symmetry-breaking fields greater than 0.05 G. The superfluid density was also found to be exponentially flat as $T\ensuremath{\rightarrow}0$ and so can be fit to a single-gap BCS model. In contrast, the lower purity sample showed an increase in the zero-field $\ensuremath{\mu}\text{SR}$ relaxation rate below ${T}_{c}$ corresponding to a characteristic field strength of 0.6 G. While the temperature dependence of the superfluid density was also found to be consistent with a single-gap BCS model, the magnitude as $T\ensuremath{\rightarrow}0$ was found to be much lower for a given applied field than in the case of the high-purity sample. These findings suggest that ${\text{Mg}}_{10}{\text{Ir}}_{19}{\text{B}}_{16}$ is a superconductor characterized by a single-gap function with no nodes and sample quality drastically affects the superconducting properties of this system.

The magnetic susceptibilities and specific heats of the crystalline garnet and glass forms of ${\text{Mn}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ are reported. This allows a direct comparison of the degree of magnetic frustration of the triangle-based garnet lattice and the structurally disordered solid at the same composition for isotropic spin $5/2\phantom{\rule{0.3em}{0ex}}{\text{Mn}}^{2+}\phantom{\rule{0.3em}{0ex}}(3{d}^{5})$. The results show that the glass phase shows more pronounced signs of magnetic frustration than the crystalline phase. Through comparison of the specific heats of ${\text{Ca}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ (grossular) and ${\text{Mn}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ (spessartine) garnets, information is provided concerning the anomalous extra specific heat in the latter material.

Although many materials display the transition from insulating to metallic behavior on doping, only a few, such as VO2, have the right combination of crystal structure and physical properties to serve as model systems. Here we report the electronic and structural characteristics of the insulator to metal transition in V1?xMoxO2, which we have studied over the range 0.0?x?0.50 through characterization of the electrical resistivity, magnetic susceptibility, specific heat, and average- and short-range crystal structures. We find that metal-metal pairing exists in small domains in the doped metallic phases and an unexpected phenomenology for the crossover between a Curie-Weiss insulating regime and an intermediate mass metallic regime. An electronic phase diagram is presented.

We report {sup 209}Bi nuclear-magnetic-resonance and nuclear-quadrupole-resonance measurements on a single crystal of the Kondo insulator U{sub 3}Bi{sub 4}Ni{sub 3}. The {sup 209}Bi nuclear-spin-lattice relaxation rate (T{sub 1}{sup -1}) shows activated behavior and is well fit by a spin gap of 220 K. The {sup 209}Bi Knight shift (K) exhibits a strong temperature dependence arising from 5f electrons, in which K is negative at high temperatures and increases as the temperature is lowered. Below 50 K, K shows a broad maximum and decreases slightly upon further cooling. Our data provide insight into the evolution of the hyperfine fields in a fully gapped Kondo insulator based on 5f electron hybridization.

Superconductivity in LaNiPO is disrupted by small (~5%) amounts of non-stoichiometry on the lanthanum site, even though the electronic contribution to the heat capacity increases with increasing non-stoichiometry. All samples also exhibit specific heat anomalies consistent with the presence of ferromagnetic spin fluctuations (Tsf ~ 14 K). Comparison of layered nickel phosphide and nickel borocarbide superconductors reveals different structure-property correlations in the two families., Comment: Submitted to Phys. Rev. B

We review the properties of Ni-based superconductors which contain Ni2X2 (X=As, P, Bi, Si, Ge, B) planes, a common structural element found also in the recently discovered FeAs superconductors. Strong evidence for the fully gapped nature of the superconducting state has come from field dependent thermal conductivity results on BaNi2As2. Coupled with the lack of magnetism, the majority of evidence suggests that the Ni-based compounds are conventional electron-phonon mediated superconductors. However, the increase in Tc in LaNiAsO with doping is anomalous, and mimics the behavior in LaFeAsO. Furthermore, comparisons of the properties of Ni- and Fe-based systems show many similarities, particularly with regards to structure-property relationships. This suggests a deeper connection between the physics of the FeAs superconductors and the related Ni-based systems which deserves further investigation., 21 pages, 4 figures, 3 tables; A review to appear in the Physica C special issue on superconducting pnictides

We report $^{75}$As Nuclear Magnetic Resonance data in a single crystal of CaFe$_2$As$_2$. The Knight shift, electric field gradient, and spin-lattice relaxation rate are strongly temperature dependent in the paramagnetic state, and change discontinuously at the structural transition temperature, $T_S=T_N=167$ K. Immediately below, the NMR spectra reveal an internal field at the As site associated with the presence of a commensurate magnetic order. These results indicate that the structural and magnetic transitions in CaFe$_2$As$_2$ are first order and strongly coupled, and that the electron density in the FeAs plane is highly sensitive to the out-of-plane structure.

We report the observation of superconductivity in ${\text{La}}_{3}{\text{Ni}}_{4}{\text{P}}_{4}{\text{O}}_{2}$ at 2.2 K. The layer stacking in this compound results in an asymmetric distribution of charge reservoir layers around the ${\text{Ni}}_{2}{\text{P}}_{2}$ planes. The estimated Wilson ratio, ${R}_{W}\ensuremath{\approx}5$, indicates the presence of strongly enhanced normal-state susceptibility, but many of the basic superconducting characteristics are conventional. The estimated electronic contribution to the specific heat, $\ensuremath{\gamma}\ensuremath{\approx}6.2\text{ }\text{mJ}\text{ }{\text{mol-Ni}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$, is about 2/3 of that found in layered nickel borocarbide superconductors.

We report an $^{75}$As NMR study of BaFe$_2$As$_2$ in both single crystals and polycrystal forms. We find that Sn impurities in the single crystal dramatically alter the low energy spin fluctuations and suppress the ordering temperature from 138 K to 85 K. In contrast to Sn-free samples, we find that the temperature dependence of the $^{75}$As NMR spectra and spin lattice relaxation rates reveal a second order phase transition to a state of incommensurate magnetic order.

We report the properties of two new isostructural compounds, U3Bi4Ni3 and U3Bi4Rh3. The first of these compounds is non-metallic, and the second is a nearly ferromagnetic metal, both as anticipated from their electron count relative to other U-based members of the larger 3-4-3 family. For U3Bi4Rh3, a logarithmic increase of C/T below 3 K, a resistivity proportional to T^4/3, and the recovery of Fermi-liquid behavior in both properties with applied fields greater than 3T, suggest that U3Bi4Rh3 may be a new example of a material displaying ferromagnetic quantum criticality.

The magnetic properties and structure of ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ for $0.5lxl1.0$ are reported. ${\mathrm{Co}}^{4+}$ is found to be high spin in ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ for $0.94\ensuremath{\leqslant}x\ensuremath{\leqslant}1.00$ and low spin for $0.50\ensuremath{\leqslant}x\ensuremath{\leqslant}0.78$. Weak antiferromagnetic coupling is observed, and at $x\ensuremath{\approx}0.65$ the temperature-independent contribution to the magnetic susceptibility and the electronic contribution to the specific heat are largest. Neutron diffraction analysis reveals that the lithium oxide layer expands perpendicular to the basal plane and the Li ions displace from their ideal octahedral sites with decreasing $x$. Comparison of the structures of ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ and ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ reveals that the $\mathrm{Co}{\mathrm{O}}_{2}$ layer changes substantially with alkali content in the former but is relatively rigid in the latter, and that the $\mathrm{Co}{\mathrm{O}}_{6}$ octahedra in ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ are less distorted.

The intermetallic perovskite MgCNi3 is a superconductor with a Tc=7 K. Substitution of Fe and Ru for Ni decreases Tc monotonically as the doping concentration is increased. Here we report thermopower measurements, S(T), on MgCNi3, MgCNi3-xFex and MgCNi3-xRux. For MgCNi3, the thermopower is negative, - 12.5 mikroV/K, at 300 K. The absolute value of S decreases as x increases in MgCNi3-xFex and MgCNi3-xRux. The sign of S changes from negative to positive at low temperatures for values of x > 0.01. These data show that the carriers in MgCNi3 are electrons, and by increasing x and decreasing temperature, the participation of hole carriers clearly increases. The influence of the magnetic moments of the Fe atoms on the thermopower is not visible.

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a=10.568 A, displaying a structure type for which no previous superconductors have been reported.

Single phase samples of the monoclinic and orthorhombic polymorphs of Nb{sub 12}O{sub 29} have been identified and isolated. These polymorphs have different arrangements of nanometer dimension structural columns of ReO{sub 3}-type niobium oxygen arrays: They differ in structure after a 3-nm translation in one of three dimensions while being the same in the other two. Magnetic susceptibility measurements show that one polymorph displays an antiferromagnetic transition at 12 K, along with short-range order fluctuations up to 25 K, while the other shows strict Curie-Weiss behavior down to 2 K.