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Synthesis of silicon nanoparticles of various sizes from 3 to 9 nm in diameter was accomplished via a low temperature solution route. These nanoparticles are prepared via reduction of SiCl4 with Na naphthalide in dimethoxyethane and capped with octasiloxane. The resulting nanoparticles were characterized by transmission electron microscopy (TEM), high resolution (HR) TEM, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction, UV–vis, photoluminescence, and their quantum yields were determined. TEM micrographs show that the nanoparticles are well dispersed and SAED and lattice fringes are consistent with diamond structured silicon. X-ray powder diffraction provides no diffraction peaks. UV–vis and photoluminescence show characteristic shifts corresponding to size, consistent with quantum confinement. The smallest sized nanoparticles show the largest quantum yield, consistent with an indirect bandgap nanoparticles.

A molten Al flux method was used to grow single crystals of the type I clathrate compound Ba8Al14Si31. Single-crystal neutron diffraction data for Ba8Al14Si31 were collected at room temperature using the SCD instrument at the Intense Pulsed Neutron Source, Argonne National Laboratory. Single-crystal neutron diffraction of Ba8Al14Si31 confirms that the Al partially occupies all of the framework sites (R1 = 0.0435, wR2 = 0.0687). Stoichiometry was determined by electron microprobe analysis, density measurements, and neutron diffraction analysis. Solid-state (27)Al NMR provides additional evidence for site preferences within the framework. This phase is best described as a framework-deficient solid solution Ba8Al14Si31, with the general formula, Ba(8)Al(x)Si(42-3/4x)[](4-1/4x) ([] indicates lattice defects). DSC measurements and powder X-ray diffraction data indicate that this is a congruently melting phase at 1416 K. Temperature-dependent resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers.

Mg3Sb2 has been prepared by direct reaction of the elements. Powder X-ray diffraction, thermal gravimetric, differential scanning calorimetery, and microprobe data were obtained on hot pressed samples. Single phase samples of Mg3Sb2 were prepared and found to contain oxygen at the grain boundaries and to lose Mg and oxidize at temperatures above 900 K. Thermoelectric properties were characterized by Seebeck, electrical resistivity, and thermal conductivity measurements from 300 to 1023 K, and the maximum zT was found to be 0.21 at ∼875 K.

Homogeneous, nanocrystalline La1-xSrxMnO3 (LSM) powders, with x ∼ 0.15, were synthesized with the epoxide addition sol−gel method. Through this simple technique, sol−gel materials were prepared from methanolic solutions of metal chlorides without the need for alkoxides, polymeric gel agents, or elaborate reaction schemes. The gels were dried in ambient conditions, resulting in mesoporous xerogels with networked nanostructures interconnecting particulate regions. Calcination of the dried gels resulted in the crystallization of single-phase LSM by 700 °C, after decomposition of intermediate hydroxide, chloride, and oxychloride compounds. SEM analysis indicated that the calcined powders were nanocrystalline and consisted of discrete particles, free of hard agglomeration. The average crystallite size and equivalent spherical diameter determined from XRD line broadening and BET analysis, respectively, were in good agreement with the SEM results (∼100 nm). The activation energies for the electronic conductivity...

Thermoelectric materials provide a key solution to energy problems through the conversion of heat into electrical energy. We report that the complex Zintl compound, Yb14MnSb11, breaks a 2-decade stagnation in high-temperature (>900 K), p-type materials development for thermoelectric power generation. This material achieves quadrupled efficiency and virtually doubled figure of merit over the current state-of-the-art, SiGe, thus earmarking it superior for thermoelectric applications in segmented devices. Yb14MnSb11 represents the first complex Zintl phase with substantially higher figure of merit and efficiency than any other competing materials, opening a new class of thermoelectric compounds with remarkable chemical and physical properties.

Various reaction conditions, such as reductant, time, procedure, concentration, and temperature, were investigated with the aim of finding a simple, optimized synthetic route for the synthesis of crystalline germanium nanoparticles. Results from these studies indicate that sodium naphthalide is an ideal reductant and that the reaction is virtually complete within 10 min. Furthermore, it was observed that a two-pot synthesis resulted in a cleaner, narrower distribution of nanoparticle size and that the narrowest size distribution (∼20%) was produced when a dilute Na(naphth) in glyme mixture was utilized. The optimum initial reduction temperature was found to be 0 °C. It was also shown that concentration and temperature play an important role in controlling nanoparticle size. The best reaction conditions, as stated above, produced nanoparticles with a size dispersion of ∼20% when combined. Transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution TEM (HRTEM), energy-...

Core/shell structured iron(Fe)/gold(Au) nanoparticles have been prepared by a reverse micelle method, and their potential application as magnetic resonance (MR) contrast agent investigated. The average nanoparticle size is 19 nm, as determined by x-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties and relaxivities of nanoparticles are presented and compared. The saturation magnetization is 81 emu g−1 Fe for freshly prepared nanoparticles and the particles have high r1(6.87 mM−1 s−1) when the Fe core is kept from oxidation. These nanoparticles may be used as T1 agents in the unoxidized form.

Single crystals of a new Zintl compound, EuIn2P2, were grown from indium metal as a flux solvent. The compound crystallizes in the hexagonal P6(3)/mmc space group with a unit cell of a = 4.0829(6) A, c = 17.595(4) A, and Z = 2. It contains alternating Eu2+ layers and [In2P2]2- layers. This compound is paramagnetic at high temperatures with a magnetic transition at 24 K. In the magnetically ordered state, it shows large magnetic anisotropy. The temperature-dependent resistivity of this compound suggests interaction between conduction electrons and local spins. Negative colossal magnetoresistance of up to −398% (MR = {[ρ(H) − ρ(0)]/ρ(H)} × 100%) at 5 T is observed at 24 K.

The electronic conductivity of tri-n-octylphosphineoxide (TOPO)-protected CdSe quantum dots (QDs) was studied at the air-water interface using the Langmuir technique within the context of photochemical and photophysical excitation. It was found that, upon photoirradiation with photon energies higher than that of the absorption threshold, the voltammetric currents increased rather substantially with a pair of voltammetric peaks at positive potentials. However, the photoconductivity profiles exhibited a dynamic transition, which was ascribed to the strong affinity of oxygen onto the CdSe surface and the consequent trapping of the photogenerated electrons. The resulting excess of holes led to photocorrosion of the particle cores. The oxygen adsorption and photoetching processes were found to be reversible upon cessation of the photoexcitation. In contrast, only featureless voltammetric responses were observed when the particle monolayers were deposited onto the electrode surface and the film conductance was measured in a vacuum (the overall profiles were analogous to that of a Coulomb blockade). A comparative study was also carried out with a CdSe dropcast thick film immersed in acetonitrile, where the photoconductivity profiles were reversible and almost linear. The latter was attributed to the separation of photogenerated electrons and holes which were subsequently collected at the electrodes under voltammetric control. In the dropcast system, the oxygen effects were minimal which was ascribed to the acetontrile medium that limited the access to oxygen and thus the particles were chemically intact. These studies suggest that chemical environment plays an important role in the determination of the chemical stability and electronic conductivity of CdSe QD thin films.

The framework-deficient clathrate phases Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29 were prepared using a molten Al flux. Single-crystal X-ray diffraction confirmed the two phases to be clathrate type I (space group Pmn). For Eu0.27Ba7.22Al13Si29, single-crystal X-ray diffraction revealed the Eu to partially occupy the 2a position. Microprobe analysis of single crystals provided the stoichiometry, and Raman spectroscopy was used to investigate the guest framework interactions. The Raman spectra are consistent with both Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29 having minimal guest-host interactions. Magnetic susceptibility data for Eu0.27Ba7.22Al13Si29 imply weak magnetic ordering and indicate a 2+ oxidation state for the Eu ion.

Butyl-capped crystalline germanium (Ge) nanoparticles were synthesized at room temperature in dimethoxyethane by reduction of GeCl4 with Na(naphthalide) and subsequent reaction with butyl Grignard. The nanoparticles were isolated in hexane and characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), elemental analysis, and X-ray powder diffraction (XRD). The product from this room-temperature reaction was heated under vacuum at temperatures of 200−600 °C at 50 °C intervals. The product obtained from the 300 °C treatment was soluble in hexane, while the products from temperatures greater than 300 °C were not. SAED was consistent with crystalline Ge from the initial synthesis at room temperature and amorphous Ge for the product heated under vacuum to 300 °C. X-ray powder diffraction of the 300 °C product shows the transition from amorphous to crystalline nanoparticles occurring between 550 and 600 °C. TEM shows that the n...

The compound Ca14MnP11 crystallizes in the Ca14AlSb11 structure type with the tetragonal space group I 4 1 / acd ( Z = 8 ) and lattice parameters of a = 15.3255 ( 7 ) A , c = 20.7565 ( 9 ) at 90 K. The structure consists of MnP49− tetrahedron, P37− trimer, 4 P3− isolated anions and 14 Ca2+ cations. Similar to other compounds of this structure type containing phosphorous, the P37− trimer has a central P atom that is best modeled in the structure as being equally split between two sites. In addition, there is no additional distortion of the manganese-containing tetrahedron compared with the main group analog, Ca14GaP11, suggesting that the Mn oxidation state is Mn2+. Temperature-dependent magnetic susceptibility shows that the compound is paramagnetic over the entire temperature range measured (2–300 K). The data can be fit with a modified Curie–Weiss law and provide an effective magnetic moment of 5.80 (2) B.M. with a Weiss constant of −2.13(2) K and χ 0 = - 9 ( 1 ) × 1 - 5 emu / mol . This moment is significantly higher than those measured for any of the Mn-containing analogs and is consistent with Mn2+. This result will be discussed in light of the electron counting scheme for Mn compounds of the Ca14AlSb11 structure-type.

Homogeneous, nanocrystalline powders of yttria-stabilized zirconia (YSZ) were prepared using a non-alkoxide sol−gel method. Monolithic gels, free of precipitation, were prepared by addition of propylene oxide to aqueous solutions of Zr4+ and Y3+ chlorides at room temperature. The gels were dried with supercritical CO2(l), resulting in amorphous aerogels that crystallized into stabilized ZrO2 following calcination at 500 °C. The aerogels and resulting crystalline products were characterized using in situ temperature profile X-ray diffraction, Raman spectroscopy, thermal analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen adsorption/desorption analysis, and elemental analysis by inductively coupled plasma-atomic emission spectroscopy. TEM and N2 adsorption/desorption analysis of an aerogel prepared by this method indicated a porous network structure with a high surface area (409 m2/g). The crystallized YSZ maintained high surface area (159 m2/g) upon formation of h...

A new rare-earth rich Zintl phase Yb11GaSb9 was synthesized by direct fusion of the corresponding elements, and large single crystals of the compound were obtained from high temperature flux synthesis. Its crystal structure was determined by single-crystal X-ray diffraction to be orthorhombic in the non-centrosymmetric space group Iba2 (No. 45), Z = 4 ( R 1 = 3.24 % , w R 2 = 6.40 % ) with a = 11.7257 ( 12 ) A , b = 12.3204 ( 13 ) A , c = 16.633 ( 2 ) A measured at 90(3) K. The structure belongs to the Ca11InSb9-type and can be viewed as built of isolated Sb4-tetrahedra centered by Ga, Sb-dimers and isolated Sb anions, which are separated by Yb2+ cations. Electron count according to the Zintl formalism suggests that the phase is electron-precise and charge-balanced, which is supported by the virtually temperature-independent magnetization for Yb11GaSb9. Electrical resistivity data from 2 to 400 K confirm that Yb11GaSb9 is a small band-gap semiconductor with room temperature resistivity ρ 298 = 45.1 m Ω cm , and low-temperature resistivity at 2 K ρ 2 = 1.9 Ω cm . As such, Yb11GaSb9 and related compounds might be promising materials for thermoelectric applications, and currently, efforts to synthesize new members of this family and test their thermoelectric performance are under way.

The chemical reactivity of current collector pastes, utilized in electrode performance measurements, were investigated with respect to the solid oxide fuel cell composite cathode, (La 85 Sr 15 ) .98 MnO 3 /8 mol% Y 2 O 3 -stabilized ZrO 2 (LSM/YSZ). Anode substrate single cells were prepared with Pt or Ag paste current collectors applied to the electrodes. Phase purity of the cathodes before and after sintering the current collectors were examined with powder X-ray diffraction (XRD) and the performance of the cells determined with current-potential measurements. XRD experiments provided evidence that Pt paste, containing a bismuth flux, reacted with the composite cathode at temperatures above 800 °C leading to formation of the pyrochlore phase, La 2 Zr 2 O 7 . Cathodes coated with Ag paste, which did not contain a bismuth flux, showed no sign of chemical degradation. Synthesized Bi-subnitrate and commercial Bi 2 O 3 were shown to have similar chemical reactions with LSM/YSZ powders leading to pyrochlore phase formation. Current-potential experiments on single test cells demonstrated that samples prepared with paste containing bismuth flux had a decrease in initial performance.

Measurements of core and valence electronic states of single crystals of the rare earth transition metal Zintl phases Yb14MnSb11 and Yb14ZnSb11 were performed using the X-ray photoelectron spectroscopy station of Beamline 7 at the Advanced Light Source. Sample surfaces of Yb14MnSb11 and Yb14ZnSb11 were measured as received, after Ar+ ion bombardment, and after cleaving in situ. The single crystal structure of Yb14ZnSb11 is also reported. Both compounds are air-sensitive and show Yb3+ due to surface oxidation. In the case of Yb14MnSb11, there is no evidence for Yb3+ that would be intrinsic to the sample, consistent with previously reported X-ray magnetic circular dichroism studies. Detailed analyses of the Yb14ZnSb11 surfaces reveal a significant contribution of both Yb3+ and Yb2+ 4f states in the valence band region. This result is predicted for the Zn analog by Zintl counting rules and support the mixed valency of Yb for Yb14ZnSb11. Further detailed analysis of the core and valence band structure of both Yb14MnSb11 and Yb14ZnSb11 is presented.

The europium-151 Mossbauer spectra of the Eu(14)MnP(11), Eu(14)MnAs(11), and Eu(14)MnSb(11) Zintl compounds, measured between 4.2 and 100 K, reveal europium(II) for all four crystallographically inequivalent europium sites in Eu(14)MnAs(11) and Eu(14)MnSb(11) and europium(II) and europium(III) for the three 32g and the 16f europium sites in Eu(14)MnP(11), respectively. Below the ordering temperatures of 52, 74, and 92 K, only very small hyperfine fields of 2-4 T are observed at the europium sites as a result of the polarization by the manganese magnetic moments. At 4.2 K, the europium(II) magnetic moments are ordered, and hyperfine fields of 24.4, 24.8, and 19.3 T are observed in Eu(14)MnP(11), Eu(14)MnAs(11), and Eu(14)MnSb(11), respectively, fields that are typical for magnetically ordered europium(II) ions. At 4.2 K the 16f europium(III) sites in Eu(14)MnP(11) experience a transferred hyperfine field of 33 T from the neighboring ordered europium(II) moments. Between its Curie temperature and 4.2 K, the europium-151 Mossbauer spectra of Eu(14)MnSb(11) reveal that the europium(II) moments order below ca. 13 K, i.e., below the second magnetic transition observed in magnetic measurements. Between their Curie temperatures and 4.2 K, the europium-151 Mossbauer spectra of Eu(14)MnP(11) and Eu(14)MnAs(11) are complex and have been analyzed with two models, models that give equivalently good fits. However, the second model in which the spectra are fit with a three-dimensional relaxation of the europium(II) and europium(III) hyperfine fields is preferred for its physical meaning and its reduced number of fitted parameters.

A new transition metal Zintl phase, Yb(9)Zn(4+x)Sb(9), was prepared by high-temperature flux syntheses as large single crystals, or by direct fusion of the corresponding elements in polycrystalline form. Its crystal structure was determined by single-crystal X-ray diffraction. Its Ca-counterpart, hitherto known as Ca(9)Zn(4)Sb(9), and the presence of nonstoichiometry in it were also studied. Yb(9)Zn(4+x)Sb(9) was found to exist in a narrow homogeneity range, as suggested from the crystallographic data at 90(3) K (orthorhombic, space group Pbam (No. 55), Z = 2): (1) a = 21.677(2) A, b = 12.3223(10) A, c = 4.5259(4) A, R1 = 3.09%, wR2 = 7.18% for Yb(9)Zn(4.23(2))Sb(9); (2) a = 21.706(2) A, b = 12.3381(13) A, c = 4.5297(5) A, R1 = 2.98%, wR2 = 5.63% for Yb(9)Zn(4.380(12))Sb(9); and (3) a = 21.700(2) A, b = 12.3400(9) A, c = 4.5339(4) A, R1 = 2.75%, wR2 = 5.65% for Yb(9)Zn(4.384(14))Sb(9). The isostructural Ca(9)Zn(4.478(8))Sb(9) has unit cell parameters a = 21.830(2) A, b = 12.4476(9) A, and c = 4.5414(3) A (R1 = 3.33%, wR2 = 5.83%). The structure type in which these compounds crystallize is related to the Ca(9)Mn(4)Bi(9) type, and can be considered an interstitially stabilized variant. Formal electron count suggests that the Yb or Ca cations are in the +2 oxidation state. This is supported by the virtually temperature-independent magnetization for Yb(9)Zn(4.5)Sb(9). Electrical resistivity data show that Yb(9)Zn(4.5)Sb(9) and Ca(9)Zn(4.5)Sb(9) are poor metals with room-temperature resistivity of 10.2 and 19.6 mOmega.cm, respectively.

Silicon nanoparticles (NPs) of ∼4.5(1.10) nm from a room-temperature solution route are terminated by a silanization method for the first time. Energy-selected emission is observed, consistent with the distribution of sizes obtained by this route. The NPs are photochemically stable in nonpolar organic solvents and when exposed to air/water under ambient conditions for up to 1 year. The nanoparticles were characterized by TEM, HRTEM, EDX, SAED, FTIR, 1H/13C NMR, UV−vis, and photoluminescence (PL) spectroscopy.

Single crystals of Na2Ti2Sb2O have been grown by NaSb flux method. It crystallizes in platelet morphology with dark silver color. The growth conditions are optimized and crystal structure has been analyzed by single crystal X-ray diffraction at 88.7, 120.0 and 150.0 K. The structure analysis result shows that there is a non-linear change in temperature-dependent lattice parameters suggesting that previously reported anomaly in temperature-dependent magnetization and electrical resistivity of polycrystalline samples around 120 K is associated with the structure distortion. Temperature-dependent magnetic susceptibility of a single crystal sample grown by NaSb flux method also exhibits a sharp transition around 120 K confirming that this anomaly is intrinsic to Na2Ti2Sb2O.

The Mg 2 Si x Ge 1 - x solid solution was prepared by heating stoichiometric amounts of elemental Mg, Si, and Ge in an argon atmosphere. Both microprobe and X-ray diffraction analysis of the reaction products suggest that homogeneous alloys can be made by heating the elements to 1200 °C, a temperature roughly 100 °C in excess of the melting temperatures for pure Mg 2 Si and Mg 2 Ge. 2 9 Si solid-state nuclear magnetic resonance was used to characterize the Mg 2 Si x Ge 1 - x solid solution. The 2 9 Si isotropic chemical shift changes consistent with the band gap in these materials while the line width increases with local disorder.

Alkyl-capped and alkyl/alkoxy-capped silicon nanocrystals have been prepared by the oxidation of magnesium silicide with bromine. High-resolution transmission electron microscopy confirmed the crystalline nature of the nanoparticles and provided an average diameter of 4.5 (2.0) nm for the alkyl-capped and for the alkyl/alkoxy-capped nanoparticles. Energy-dispersive X-ray spectroscopy showed that the nanoparticles are composed of silicon, with no evidence of unreacted bromine. FTIR spectra were consistent with alkyl- and alkyl/alkoxy-capped surfaces. Fluorescence spectroscopy indicated strong ultraviolet-blue photoluminescence, which was attributed to both quantum confinement and surface termination. These nanoparticles displayed long-term stability and no degradation of the photoluminescence was observed for a period of 1 year.

As part of our continuing efforts to study the molecular events involved in HIV recognition of mucosal membrane cells, we are studying the interactions of the HIV-associated glycoprotein gp120, with the cellular receptor GalCer. In this work, we report investigations of multivalent interactions of Au glyconanoparticles containing galactosyl and glucosyl headgroups with recombinant gp120. These particles were prepared from disulfides containing C-glycosides linked to triethylene glycol via an amide bond using a modification of the Brust method.1 Results from transmission electron microscopy, atomic force microscopy, and UV−vis absorption spectroscopy data are consistent with an average particle diameter of 2 nm. Elemental analyses indicate that the average composition of the particles is 1.6:1 Au:carbohydrate. A biotin−NeutrAvidin adhesion assay was used to evaluate the relative ability of carbohydrate disulfides and Au glyconanopraticles to displace rgp120 from plate-bound GalCer. The data indicate that d...

Boyd R. Taylor *, Glenn A. Fox , Lousia J. Hope-Weeks , Robert S. Maxwell , Susan M. Kauzlarich , Howard W.H. Lee d a Chemistry and Chemical Engineering Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA b Analytical and Nuclear Chemistry Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA c Chemistry Department, University of California, One Shields Avenue, Davis, CA 95616, USA d UltraPhotonics Inc., 48611 Warm Springs Blvd. Fremont, CA 94536, USA

We describe the synthesis and characterization of nanocrystalline Si prepared by the initial reaction of the metal silicide, Mg 2 Si, with either SiCl 4 or Br 2 and, subsequently, with LiAlH 4 . These reactions produce Si nanoparticles with surfaces that are covalently terminated with H. The resultant nanoparticles can be suspended in organic solvent and are characterized by Fourier transform infrared (FTIR), UV–vis absorption, and photoluminescence (PL) spectroscopy. This work provides the first direct evidence of hydrogen terminated Si nanoparticles synthesized in solution.

The magnetic ordering of the tetragonal Ca 14 MnSb 11 compound (space group I 4 1 / acd ) has been determined by high-resolution neutron diffraction on powder samples. Neutron data were obtained at temperatures of 1.4, 10, 95 K, and room temperature. Refinement of the magnetic structure reveals a ferromagnetic ordering of Mn magnetic moments lying in the a – b plane below the T C of 63 K. The low-temperature-ordered magnetic moment on the Mn ion is 3.4(2) μ B at 1.4 K. The results are confirmed by magnetic susceptibility measurements, which show that the easy magnetization direction of the compound is perpendicular to the c -axis and the system orders ferromagnetically at 63 K, in good agreement with neutron diffraction results. A large negative magnetoresistance effect (Δ ρ / ρ ( H )=−34.4%) at the magnetic transition temperature is observed in applied magnetic fields up to 6 T.

X-ray magnetic circular dichroism (XMCD) measurements on Yb14MnSb11 provide experimental evidence of a moment of 5 microB on Mn, with partial cancellation by an opposing moment on the Sb4 cage surrounding each Mn ion. The compound is isostructural to Ca14AlSb11, with Mn occupying the Al site in the AlSb4(9-) discrete tetrahedral, anionic unit. Bulk magnetization measurements indicate a saturation moment of 3.90 +/- 0.02 microB/formula unit consistent with four unpaired spins and implying a Mn3+, high-spin d4 state. XMCD measurements reveal that there is strong dichroism in the Mn L23 edge, the Sb M45 edge shows a weak dichroism indicating antialignment to the Mn, and the Yb N45 edge shows no dichroism. Comparisons of the Mn spectra with theoretical models for Mn2+ show excellent agreement. The bulk magnetization can be understood as Mn with a moment of 5 microB and a 2+ configuration, with cancellation of one spin by an antialigned moment from the Sb 5p band of the Sb4 cage surrounding the Mn.

The solid solution of the ternary transition metal Zintl phase Ca 14-x Eu x MnSb 11 (0 < x < 14) has been prepared by heating a mixture of stoichiometric amounts of the elements in a two-zone furnace with T high = 1100 °C and T low = 1050 °C. The ternary transition metal compounds crystallize in the tetragonal space group I4 1 /acd and are isostructural with the Zintl compound Ca 14 AlSb 11 . The lattice parameters of the Ca 14-x Eu x MnSb 11 compounds linearly increase with increasing Eu substitution for Ca. The Eu atoms preferentially occupy the C a (2) site first and subsequently occupy Ca(4), Ca(1), and Ca(3), in order, among the four crystallographically inequivalent Ca sites. Temperature-dependent magnetic susceptibility measurements of the solid solution reveal that Eu replacement for Ca induces complex magnetic interactions in the compound, from simple ferromagnetic interactions for Ca 14 -MnSb 11 to ferrimagnetic interactions for Eu 14 MnSb 11 , because of the Eu 2+ (4f 7 ) magnetic moment. The paramagnetic Curie temperature of the Ca 14-x Eu x MnSb 11 compounds shows an interesting change with varying x, and the magnetic easy axis gradually changes in the solid solution from perpendicular (for Ca 14 MnSb 11 ) to parallel (for Eu 14 MnSb 11 ) to the crystal c axis. The electrical transport properties of the Ca 14-x Eu x MnSb 11 (x = 0, 3, 11) compounds show a close relation to their magnetic properties and are compared to the previous results for Ca 14-x Eu x MnSb 11 (x = 13, 14). The influence of Eu doping on the structural and physical property of Ca 14-x Eu x MnSb 11 is discussed in terms of the site preferences of Eu for the four different Ca sites.

The compounds Ca14AlP11, Ca14MnP11, and Eu14MnP11 have been synthesized and are isostructural to the Zintl compound, Ca14AlSb11. Eu14MnP11 is a ferromagnet showing colossal magnetoresistance at TC = 52 K, Ca14MnP11 shows paramagnetic behavior down to 5 K, and Ca14AlP11 is nonmagnetic. The formula unit for these Zintl compounds is A14MPn11 and comprises 14 A cations, a MPn4 tetrahedron, four isolated Pn anions, and a Pn3 linear unit. The central Pn of the Pn3 unit is believed to be positionally disordered, and it has been speculated that the disorder is static rather than dynamic. To address this issue, 31P solid-state NMR was applied to these new compounds to provide insight into the magnetic ordering and structural changes. The NMR chemical shift anisotropy and the dipolar coupling for the 31P nuclei as well as the quadrupolar coupling for the 27Al nucleus in the diamagnetic compound Ca14AlP11 provide structural details consistent with the Zintl structure. Wide-line 31P NMR and EPR were applied to the pa...

In the course of our investigation aimed at the preparation of anisotropic cluster materials using a combination of oxide and chloride ligands to induce directional bonding preferences in the cluster unit, a series of niobium oxychloride cluster compounds AxNb6Cl12O2 (A=K, x=0.72(2); A=Rb, x=0.736(7); A=Cs, x=0.938(4); A=In, x=0.634(8)) was obtained by solid state synthesis. The cluster framework is based on (Nb6Cl10iO2i)Cl4aO2a clusters connected via oxide ligands in the a → direction with two Nb–O linkages between adjacent clusters, which resembles intercluster bonding in Chevrel–Sergent phases, while in the other two directions, the linkages occur through single Cla–a bridges. The framework generates channels where the cations A+ are located. The electronic band structure of the series features a narrow partially occupied band originating from a Nb–Nb bonding state. Magnetic and ESR measurements show the presence of localized unpaired electrons, and resistivity measurements indicate a semiconducting behavior.

Large single crystals of EuSnP were grown from a tin flux. The crystal structure of EuSnP is the NbCrN structure type. The new compound crystallizes in the tetragonal system, space group P4/nmm, with the lattice constants a=4.2783(6) A and c=8.762(2) A, at T=130 K (Z=2, R1=0.0382, wR2=0.1002). Temperature-dependent magnetic susceptibility measurements on single crystals indicate that EuSnP is an antiferromagnet with a Neel temperature of 21 K. The high temperature paramagnetic data can be fit to a Curie–Weiss law and are consistent with the assignment of a 2+ valence to the Eu ions, seven unpaired electrons. The magnetic susceptibility below the Neel temperature is anisotropic, showing a metamagnetic transition when the field is applied perpendicular to the crystallographic c axis. A spin-reorientation occurs below the Neel temperature with an applied critical field, Hc=1.5 Tesla at 2 K. Temperature dependent resistivity indicates metallic behavior with a negative magnetoresistive transition at the magnetic ordering temperature. This transition is suppressed with magnetic field.

The effect of four different dopants (Ca, Sr, Ba, and Yb) on the structural and physical properties of the ternary rare-earth transition metal compound, Eu14MnSb11, has been investigated. The compounds, Eu14-xAxMnSb11 (A = Ca, Sr, Ba, and Yb, x = 1), have been prepared by heating the mixture of stoichiometric amounts of the elements, sealed in a quartz jacketed Ta tube, in a two-zone furnace with Thigh = 1100 °C and Tlow = 1050 °C for 10 days. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd, Z = 8. The lattice parameters of the doped compound increase correspondingly as the radius of the metal dopant (A2+) increases. The preference of the dopants onto the four crystallographically inequivalent sites of Eu was examined by single-crystal X-ray diffraction. The magnetization of the compounds has been measured as a function of temperature and applied magnetic field. Temperature-dependent magnetic susceptibility measurement of powder sa...

Large single crystals of EuMn2P2 were grown from a tin flux whose melt composition and reaction temperature profile were optimized to avoid impurity phases. The crystal structure of EuMn2P2 is of the CaAl2Si2 structure type. The structure was determined by single-crystal X-ray crystallography, with the unit cell in the trigonal lattice, a=4.1294(3) A and c=6.9936(8) A, at T=90 K (Z=1, R1=0.0239, wR2=0.0632) and belongs to the P 3 m1 (#164) space group. Temperature-dependent magnetic susceptibility, resistivity, and neutron diffraction measurements on single crystals indicate that EuMn2P2 is an antiferromagnetic insulator with a Neel temperature of 16.5±0.25 K. The Eu spins order in a simple magnetic structure where the spins in the a–b plane are aligned ferromagnetically; these ferromagnetic planes are stacked antiferromagnetically along the c-axis.

The synthesis, spectroscopic and structural characterization of three new lithium derivatives of terphenyl ligands are reported. These are the mixed lithium alkyl–lithium aryl compound {Li(t-Bu)LiC6H3-2,6-Trip2} (1, Trip=C6H2-2,4,6-i-Pr3), the dilithiated {LiC6H3-2-(C6H3-2-Me-5-t-Bu)-6-(C6H3-2-CH2Li-5-t-Bu)·Et2O}2 (2), and the ether solvated (Et2O)LiC6H3-2,6-(C6H4-4-t-Bu)2 (3). The synthesis of the terphenyl halide precursors for 2 and 3 is also given. The compound 1 resulted from the treatment of 1-IC6H3-2,6-Trip with two equivalents of Li(t-Bu) in hexane. It features the alkyl and aryl (terphenyl) groups bridged by two lithium ions. The lithium ions are further solvated by ortho aryl substituents and methyls of the t-Bu groups. This compound is a very rare example of a mixed lithium alkyl–lithium aryl species. Compound 2 was obtained in low yield from the treatment of 1-BrC6H3-2,6-(C6H3-2-Me-5-t-Bu)2 with two equivalents of Li(t-Bu). The terphenyl ligand was dilithiated by replacement of the bromine and a hydrogen from one of the methyl groups on the ortho aryl substituents. The ether solvated, dimeric, tetrametallic structure illustrated in the Table of Contents resulted. The compound 3 was obtained from the straightforward lithiation of the iodoterphenyl precursor in the presence of diethyl ether and features a lithium ion solvated by two ethers terminally bound to the ipso-carbon of the terphenyl group.

The synthesis, crystal structure, magnetic properties, and europium Mössbauer spectroscopy of the new members of the 9-4-9 Zintl family of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) (CM = coinage metal: Au, Ag, and Cu) are reported. These compounds crystallize in the Ca(9)Mn(4)Bi(9) structure type (9-4-9) with the 4g interstitial site almost half-occupied by coinage metals; these are the first members in the 9-4-9 family where the interstitial positions are occupied by a monovalent metal. All previously known compounds with this structure type include divalent interstitials where these interstitials are typically the same as the transition metals in the anionic framework. Single-crystal magnetic susceptibility data indicate paramagnetic behavior for all three compounds with antiferromagnetic ordering below 10 K (at 100 Oe) that shifts to lower temperature (7 K) by applying a 3 T magnetic field. (151)Eu Mössbauer spectra were collected on polycrystalline powder samples of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) at 50 and 6.5 K in order to evaluate the valence of Eu cations. Although the Zintl formalism states that the five crystallographically distinct Eu sites in Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb9 should bear Eu(2+), the Mössbauer spectral isomer shifts are clearly indicative of both 2+ and 3+ valence of the Eu cations with the Cu- and Au-containing compounds showing higher amounts of Eu(3+). This electronic configuration leads to an excess of negative charge in these compounds that contradicts the expected valence-precise requirement of Zintl phases. The spectra obtained at 6.5 K reveal magnetic ordering for both Eu(2+) and Eu(3+). The field dependence of Eu(2+) indicates two distinct magnetic sublattices, with higher and lower fields, and of a small field for Eu(3+). The site symmetry of the five Eu sites is not distinguishable from the Mössbauer data.

Octanol capped silicon nanoparticles crystallizing in the metastable BC8 structure are prepared by a colloidal route from mixtures of SiI4, n-butyllithium, dioctylether, and 1-octanol (280 °C, 72 h, 25—35% yield).

Single crystals of the title compounds are prepared from the elements in a Sn flux (alumina crucibles, 950 °C, 96 h) and characterized by powder and single crystal XRD, transport properties measurements, and TB-LMTO-ASA electronic structure calculations.

The compounds, Eu14-xCaxMnSb11 (x < 3), have been prepared by heating the mixture of stoichiometric amounts of the elements, sealed in a quartz-jacketed Ta tube, in a two-zone furnace with Thigh = ...

The compounds Na2Ti2Pn2O (Pn = As, Sb) crystallize in the anti-K2NiF4 structure type in the space group, I4/mmm, with Z = 2 and the lattice parameters a = 4.0810(9) A and c = 15.311(3) A for the As analogue at 310 K and a = 4.160(2) A and c = 16.558(7) A for the Sb analogue at 150 K. The structure consists of edge-shared [Ti4/2Pn2O4/4]2- layers separated by double layers of Na+. These compounds exhibit an anomalous transition in the temperature-dependent magnetic susceptibility at = 330 K for the As analogue and = 120 K for the Sb analogue. Temperature-dependent powder neutron diffraction has been performed to investigate the magnetic spin ordering and structure symmetry breakdown of the compounds; however, no scattering due to magnetic spin ordering or symmetry change has been detected. The temperature-dependent electrical resistivity of these compounds also exhibits an anomaly reminiscent of CDW (charge-density-wave)/SDW (spin-density-wave) materials. The As analogue shows an insulator-to-insulator tran...

The new compounds Eu14MnAs11 and Eu14MnP11 were synthesized from stoichiometric amounts of the elements. The compounds are isotypic to Ca14AlSb11 and crystallize in the tetragonal space group I41/acd (Z = 8). Lattice parameters obtained from single-crystal X-ray diffraction at 130 K are a = 16.318 (2) A, c = 21.684 (4) A and a = 15.930 (4) A, c = 21.213 (5) A for Eu14MnAs11 and Eu14MnP11, respectively. In the refinement of each structure, the central Pn(4) site of a Pn37- linear unit (Pn = As, P) shows positional disorder; this is in contrast to the ordered structures formed when Pn = Sb and Bi. Eu14MnAs11 and Eu14MnP11 are ferromagnetic with transitions at 74 and 52 K, respectively. Eu14MnAs11 also has a low-temperature transition at ∼25 K. Resistivity measurements indicate an insulator-to-metal transition near the magnetic transition, and plots of ln ρ vs 1/T are linear above TC, providing activation energies of 0.03 eV (As; 240−300 K) and 0.31 eV (P). The resistivity is suppressed in the presence of a ...

The new pnictide oxide Sr2MnZn2As2O2 is reported. The crystal structure of this compound consists of a 1:1 intergrowth of square-planar MnO22- layers and ThCr2Si2-type Zn2As22- layers interspersed by Sr cations. This compound has been prepared by sintering the stoichiometric ratio of SrO, Mn, Zn, and As in a fused-silica ampule under 0.2 atm of Ar at 1000 °C for 1 week. The sample quality has been examined by Rietveld refinement of the powder X-ray diffraction data, and the transition metal site (2a and 4d) selectivity has been analyzed by Rietveld refinement of powder neutron diffraction data. Furthermore, effects of this structural order on the magnetic susceptibility and interaction between the magnetic layers have been analyzed by temperature-dependent magnetization measurements. The magnetic structures of both phases, A2MnZn2As2O2 (A = Sr, Ba), have been investigated by temperature-dependent powder neutron diffraction. The Ba analogue exhibits two-dimensional short-range order below about 40 K, where...

The new pseudo-binary intermetallic compound, Ti 11 (Sb,Sn) 8 , has been synthesized by reacting Ti and Sb in a Sn flux at 1100°C and its structure determined from both single-crystal X-ray and neutron diffraction data (orthorhombic, Pnma , Z=4, X-ray diffraction at 90 K: a =14.6877(6) A, b =5.5677(2) A, c =17.7207(7) A, V =1449.14(10) A 3 , neutron diffraction at room temperature: a =14.677(6) A, b =5.577(3) A, c =17.716 (6) A, V =1450(1) A 3 ). The structure contains two differently oriented repeating layers and interstitial atoms that are closely connected to make linear chains aligned along the crystal b axis. The compound exhibits mixed site occupancies of Sb and Sn on the anion sites. The phase width (Sb/Sn ratio=0.98–1.40) was determined by microprobe elemental analysis. The electrical resistivity of a single crystal as a function of temperature is anisotropic ( ρ //b =1∼2×10 −1 mΩ·cm, ρ ⊥b =0.5×10 −1 mΩ·cm) and confirms that this compound is metallic. Magnetic susceptibility measurements show Pauli paramagnetism.

The synthesis of silicon nanoclusters and their characterization by multinuclear solid-state nuclear magnetic resonance (NMR) is presented. A combination of 23Na, 29Si, and 13C magic angle spinning with and without cross polarization to 1H nuclei have been used to investigate the reaction of sodium silicide (NaSi) with silicon tetrachloride (SiCl4) followed by varying degrees of surface passivation. The 23Na and 29Si NMR spectra of NaSi distinguish the two crystallographically inequivalent sites for each, consistent with the crystal structure. This compound exhibits extreme diamagnetic chemical shifts for 29Si of −361 and −366 ppm. NaSi is reacted with SiCl4 in refluxing ethylene glycol dimethyl ether to produce both amorphous and crystalline Si nanoparticles with surfaces capped by chlorine. This reaction produces new 29Si resonances that survive subsequent capping and oxidation reactions. The 29Si NMR spectrum shows that the product is incompletely passivated with butyl groups and gives several peaks ly...

The compounds Eu16Sb11 and Eu16Bi11 have been prepared from the elements in Ta containers by heating at 1100°C and then slowly cooled to 1000°C over 4 days.These compounds are isostructural with the Zintl-phase Ca16Sb11 and crystallize in the tetragonal space group P 4 21m (Z=2). The structures were determined from single-crystal X-ray data (T=143 K) for Eu16Sb11 (a=12.674 (2) A, c=11.720 (2) A, R1=4.04% wR2=0.84%), and Eu16Bi11 (a=12.885 (2) A, c=11.883 (4) A, R1=6.09%, wR2=15.24%). The Ca16Sb11 structure type can be described as pairs of face-shared square antiprisms that are joined by means of a square prism to form a columnar chain composed of Ca2+ cations and centered by Sb anions along the c axis. The columns are associated by means of Ca–Ca bonds that alternate long and short along the c axis in a ladder-like fashion. Along the a and b axes, there is an intergrowth of square prism, antiprism columns alternating with columns of face-sharing hexagonal antiprisms. The structures of these Eu compounds are compared with those of Ca16Sb11. Temperature-dependent resistivity of Eu16Sb11 indicates that it is a semiconductor. Magnetization measurements show that Eu16Sb11 and Eu16Bi11 are paramagnetic. The effective moment in the paramagnetic state for Eu16Sb11 is μexp=32.2 (1) μB per formula unit (8.06 (3) μB/Eu atom) and for Eu16Bi11, μexp=33.6 (2) μB/formula unit (8.40 (6) μB/Eu atom), consistent with divalent Eu2+ cations (μeff=7.94 μB/Eu atom).

The structure of Na 2 Ti 2 Sb 2 O has been investigated by temperature-dependent powder neutron diffraction. Na 2 Ti 2 Sb 2 O crystallizes in I 4/ mmm symmetry. The structure of this phase can be viewed as an anti-K 2 NiF 4 type where Ti 3+ ion is located between two oxygen atoms forming a square-planar lattice. Powder neutron diffraction studies of Na 2 Ti 2 Sb 2 O indicate that this compound has a structural distortion in the [Ti 2 Sb 2 O] 2− layer at T ≈120 K. This transition corresponds well to the previously reported anomalous transition temperature of the magnetic susceptibility and electronic resistivity. Several models to explain the data are presented and discussed.

The results of thermodynamic, transport, and x-ray diffraction measurements of single crystals of the new compound Yb14ZnSb11 are presented. These data indicate an intermediate Yb valence scenario, with a spin fluctuation temperature of approximately 85 K. The compound is weakly metallic and is isostructural with the charge-balanced Zintl compound Yb14AlSb11. The intermediate Yb valence can be qualitatively accounted for by considering the charge counting arguments of the nonmetallic parent, and charge balance in Zintl-related materials appears to be a viable route to designing other compounds with intermediate valence constituents.

We present results from a numerical investigation of bilayer classical spin systems with local interactions and frustration caused by lattice geometry. We find that when two identical square planes are displaced by half a lattice constant in one direction, a transition to a uniformly twisted spin state occurs at ${J/J}_{\ensuremath{\perp}}g~0.25.$ An orthogonal state between layers is obtained in the limit $T=0$ and ${J}_{\ensuremath{\perp}}=0.$ If instead the two layers are offset along a diagonal, we obtain the phase diagram of the classical ${J}_{1}\ensuremath{-}{J}_{2}$ model. A weakly canted phase is observed at the classical transition point of ${J/J}_{\ensuremath{\perp}}=0.5,$ but frustration does not drive the system towards a state of orthogonal interlayer order. We propose a simple bilayer model with two inequivalent square lattices to study the frustrating interactions of the mixed layer pnictide oxides $({\mathrm{Sr}}_{2}{\mathrm{Mn}}_{3}{\mathrm{Pn}}_{2}{\mathrm{O}}_{2},\mathrm{ }\mathrm{Pn}=\mathrm{As},\mathrm{Sb}).$ We find a ground state composed of two independent N\'eel ordered layers when the interlayer exchange is an order of magnitude weaker than the intralayer exchange, as suggested by experiment. Evidence for local orthogonal order between the layers is found, but it occurs in regions of parameter space which are not experimentally realized.

Nanometer-sized tin, Sn/R, and Sn/Si−R (R = n-C4H9), core/shell nanoparticles have been prepared by the reaction of SnCl4 or SiCl4 with Mg2Sn in ethylene glycol dimethyl ether (glyme) and subsequently with n-C4H9Li. Sn/SiO2 core/shell nanoparticles are produced from the reaction of Mg2Sn with SiCl4 and subsequent reaction with H2O2. Fourier transform Infrared (FTIR) spectra are consistent with n-butyl surface termination for the n-butyl-capped tin (Sn/n-butyl) and the silicon-n-butyl capped tin (Sn/Si-n-butyl) core/shell nanoparticles. High-resolution transmission electron microscope (HRTEM) confirms that the core part of Sn/n-butyl and Sn/Si- n-butyl nanoparticles is consistent with the tetragonal structure of tin, exhibiting lattice fringes of the {200} crystal plane (2.92 A). The FTIR spectrum of Sn/SiO2 confirms the evidence of silica capping and selected area electron diffraction (SAED) is consistent with an amorphous shell (SiO2) and crystalline Sn core. Solid-state nuclear magnetic resonance (NMR) ...

Photoluminescence (PL) from alkyl-terminated silicon nanocrystallites as a function of size has been studied. Ultraviolet–blue luminescence (390–410 nm) is observed from as-prepared silicon nanoclusters with diameters from 3 to 8 nm. After 1 h of annealing at 162°C in 2-methoxyethyl ether (diglyme), the λ max of PL shifts from 360 to 420 nm. High-resolution transmission electron microscopy (HRTEM) images show that individual silicon nanoparticles are fused to form pairs of nanoparticles. FTIR spectra show that the alkyl groups remain on the surface of silicon nanoparticles. As the temperature is raised to 250°C for 1 h, the PL no longer shows any peak in the visible light region. TEM images show that the silicon nanoparticles are aggregated and fused uniformly in one single dimension, to form a strip, and these strips parallel each other. When the temperature is raised to 350°C these silicon nanoparticles form a large piece of silicon textile network, showing that functionalized alkyl surface does not persist above this temperature. A strong Si–O–Si asymmetric stretching vibration appears between 1000 and 1100 cm−1 at the expense of the C–H vibrational modes and there is no more change after 3 h of annealing at 250 or 350°C. These results provide strong evidence that the PL originates from quantum confinement.

The synthesis, crystal structure, magnetization, and resistivity of Gd-doped ${\mathrm{Eu}}_{14}{\mathrm{MnSb}}_{11}{,\mathrm{}\mathrm{Eu}}_{13.97}{\mathrm{Gd}}_{0.03}{\mathrm{MnSb}}_{11},$ are reported and compared to ${\mathrm{Eu}}_{14}{\mathrm{MnSb}}_{11}$ and ${\mathrm{Eu}}_{14}{\mathrm{MnBi}}_{11}.$ All three compounds are isostructural with the Zintl compound ${\mathrm{Ca}}_{14}{\mathrm{AlSb}}_{11}.$ The Gd-doped Eu transition metal Zintl compound crystallizes in the tetragonal space group ${I4}_{1}/\mathit{acd}$ with $a=17.338(3)\AA{}$ and $c=22.691(5)\AA{},$ where Gd partially replaces Eu in the structure. The compound displays three magnetic phase transitions: a ferromagnetic transition near 80 K, an apparent antiferromagnetic transition at a field-dependent ${T}_{N}$ ${(T}_{N}=30\mathrm{K}$ in zero field), and a spin-reorientation transition with a transition temperature that is near 15 K in zero field but is also field dependent. Measurements of both zero-field resistivity for $5l~Tl~300\mathrm{K}$ and the magnetoresistance in fields up to 5 T for the same temperatures are presented. Negative magnetoresistance is observed over a wide range of temperatures below 200 K.