Mixed Network Former Effect in Ion-Conducting Alkali Borophosphate Glasses: Structure/Property Correlations in the System [M2O]1/3[(B2O3)x(P2O5)1–x]2/3 (M = Li, K, Cs)

Glasses in the system [M2O]1/3[(B2O3)x(P2O5)1–x]2/3(M = Li, K, Cs) (0.0 ≤ x ≤ 1.0) were prepared by standard melt-quenching procedures, and their physical properties were characterized by thermal analysis, density measurements, and impedance spectroscopy. Their atomic level structures were comprehensively characterized by Raman spectroscopy, by X-ray photoelectron spectroscopy (XPS), and by 11B, 31P, and 7Li as well as 133Cs high resolution solid state magic-angle-spinning (MAS) NMR techniques. 31P MAS NMR peak assignments were aided by the presence or absence of homonuclear indirect 31P–31P spin–spin interactions, “J-coupling”, as detected via refocused INADEQUATE techniques. Consistent speciations of the phosphate and borate network former components in terms of the various PnmB and BnmPunits, where n is the number of bridging oxygens (BOs) and m is the number of B or P units bonded to P or B, respectively, present in these glasses were derived from 11B MAS NMR, combined with both 31P MAS NMR and XPS line shape analyses, constrained by charge and mass balance considerations. The speciation of the BO species in the glassy network was quantified both by O 1s XPS and 11B{31P} rotational echo double resonance spectroscopy. Both experiments indicate a strong preference of heteroatomic B–O–P over homoatomic P–O–P and B–O–B linkages to the extent that close to the maximum number of possible B4–O–P linkages is formed. Further, the structural speciations of the borate and phosphate species, together with bond valence (BV) analyses of the charge redistribution on the various structural units, indicate that the alkali network modifier oxide is not proportionally shared between the two network former components B and P in these systems. Rather, the amounts and types of the various borate and phosphate species are found to be consistent with the negative charge brought in by the alkali modifier M2O being distributed more toward the phosphate structural units which are suggested to attract a larger concentration of network modifier species than predicted by the bulk composition. The experimental results obtained from these studies help in understanding the strongly nonlinear compositional dependence of the glass transition temperature and the ionic conductivity in terms of detailed atomic-level structural information. The emerging structural principles appear to be general to all of the alkali borophosphate glass systems, with the type of alkali ion network modifier producing only minor variations

Spectral editing based on scalar spin-spin interactions: new results on the structure of metathiophosphate glasses

The local structure of glassy 'NA'P'S IND.3' and 'AG'P'S IND.3' was analyzed based on quantitative 'ANTPOT.31 P' MAS-NMR spectroscopy. The glasses contain some oxide impurities, which could be quantified from the NMR spectral analysis. Four discrete resonances are observed in both glasses, which were assigned to four distinct types of phosphate groups 'P POT.(n)', where n is the number of P-S-P bridges(i.e., 'P POT.(0)', 'P POT.(1)', 'P POT.(2)', and 'P POT.(3)' units, respectively) with the help of 2D homonuclear J-resolved and INADEQUATE methods. Based on the results obtained, the interpretations of previous spectra obtained at low spinning speeds on lithium and silver thiophosphate glasses (Chem. Mater. 2 (1990), 273, and J. Am. Chem. Soc. 114 (1992), 5775) need to be revised. Contrary to the situation in alkali phosphate glasses, the corresponding sulfide analogs are characterized by a wide 'P POT.(n)' species distribution close to that predicted by a statistical charge distribution. INADEQUATE experiments fail to detect 'P POT.(n)' 'P - POT.(n-1)' connectivities, suggesting that the structure of these glasses is rather inhomogeneous, possibly featuring the different 'P POT.(n)' species in segregated domains

Preparation and characterization of Na2O-Al2O3-B2O3 sol-gel glasses with aluminum lactate and formiate as precursors

In this work aluminum lactate and aluminum formiate have been used as precursors to obtain room temperature stable sols and gels and after annealing homogeneous glasses in the System Na2O-Al2O3-B2O3. The local environments and connectivities of boron and aluminum have been investigated by 11B and 27Al solid-state nuclear magnetic resonance (NMR). It was found that the local atomic structures of the sol-gel glasses markedly depend on the precursors and the preparation routes and are also dissimilar to those of melt quenched glasses of the same compositions. Thus, for example, the fractions of BO3/2 and BO4/2 units differ and it is interesting to note that there are no asymmetric ΒO2/2(O-) units present in the sol-gel materials. The 27Al spectra show AI in four-, five- and sixfold coordination, whose relative abundance in a given glass composition is also dependent on the preparadon route. Rotational echo double resonance (REDOR) 11B {27Al} and 27Al {11B} resuhs indicate that the extent of B-O-Al connectivity is diminished in the gel prepared glasses when compared to the melt cooled glasses. Element distributions are reported on the basis of secondary neutral mass spectrometry (SNMS) data, and the nanostructures of surfaces have been characterized by atomic force microscopy (AFM)

Α multi-method characterization of borosilicate glasses doped with 1 up to 10 mol% of Fe, Ti and Sb

The model glasses NBS1 and NBS2 are sodium borosilicate glasses of high intrinsic UV transmission. Although both glasses have an SiO2 content of 74 mol%, they possess different matrix structures due to varied Na2O / B2O3 ratios. Nonbridging oxygens occur in the NBS1 but not in the NBS2 glass. Fe, Ti and Sb oxides were added at concentrations of 1 and 10mol% to study valence, coordination and site distribution. XANES, Mössbauer, optical absorption, photoluminescence and EPR spectroscopy provided an insight into the structures and near range environments of the dopants. Large differences were found for the two Fe doped glasses. The presence of nonbridging oxygens in NBS1 glass leads to a higher solubility of the Fe ions and a higher ratio of tetrahedral over octahedral Fe3+ coordination while a clustering of Fe ions resulting in a lowered UV and VIS transmission is observed in NBS2 glass. In Ti doped glasses EPR and XANES spectroscopy shows that most Ti occurs as Ti4+, in four-, five- and sixfold coordination. Optical spectra of Ti4+ display high intensity charge transfer transitions in the UV region. Ti4+ photoluminescence in the visible range is of low intensity. Optical absorption, XANES and Mössbauer spectroscopy could only detect Sb3+ in the antimony doped glasses. The photoluminescence of Sb3+ is much stronger in the NBS1 than in the NBS2 glass

New hypodiphosphates of the alkali metals: Synthesis, crystal structure and\ud vibrational spectra of the hypodiphosphates(IV) M2[(H2P2O6)(H4P2O6)]\ud (M¼Rb and Cs)

The new hypodiphosphates(IV) Rb2[(H2P2O6)(H4P2O6)] (1) and Cs2[(H2P2O6)(H4P2O6)] (2) were synthesized by soft chemistry reactions from aqueous solutions of hypophosphoric acid and the corresponding heavy alkali-metal carbonates. Their crystal structures were determined by single crystal X-ray diffraction. Both compounds crystallize isotypic in the triclinic space group P-1 with one formula unit in the unit cell. The structures are built up by discrete (H2P2O6)2− and (H4P2O6) units in staggered conformation for the P2O6 skeleton and the corresponding alkali-metal cations. In the (H2P2O6)2− ion the hydrogen atoms are in a “trans–trans” conformation. O·H–O hydrogen bonds between the (H2P2O6)2− and (H4P2O6) groups consolidate the structures into a three-dimensional network. The FT-Raman and 31P and 1H and MAS NMR spectra of the title compounds have been recorded and interpreted, especially with respect to their assignment to the (H2P2O6)2− and (H4P2O6) groups. Thermogravimetric data of 2 have been interpreted in terms of a thermal decomposition model.Fonds der Chemischen IndustrieNRW Forschungsschule ‘‘Molecules and Materials’

Structure of ternary aluminum metaphosphate glasses

Ternary metaphosphate glasses in the systems (1 - x)NaPO3·xAl(PO3)3, (1 -x)KPO3·xAl(PO3)3, and (1 - x)Pb(PO3)2·xAl(PO3)3 (0 ≤ x ≤ 1) were analyzed using a set of 31P, 27Al, and 23Na high-resolution NMR and X-ray photoelectron spectroscopy techniques, to determine the phosphate speciation and the short- and medium-range order properties of the P and Al connectivity. O-1s XPS data confirm that the number of oxygen atoms linking two phosphorus remains close to 33% for all of the glasses, consistent with the exclusive presence of Q2 units, in agreement with 31P MAS NMR data. The increasing formation of Al-O-P linkages with increasing x is indicated by a new O-1s peak, with binding energies near 532 eV, and systematic changes in the 31P MAS NMR chemical shifts. The presence of Q2m phosphate groups (m being the number of P-O-Al bonds per tetrahedron, 0 ≤ m ≤ 2) was analyzed by 31P MAS NMR and 31P{27Al} REAPDOR experiments. The REDOR technique was applied to the heteronuclear spin systems 31P/27Al and 31P/23Na, to analyze the local structure around these species. 27Al MAS NMR and 27Al triple quantum MAS were applied respectively to determine the coordination state of Al and the values of isotropic chemical shift and electric quadrupole coupling parameters of 27Al. The results points to common features in the glass structure of these ternary phosphates. The most probable environment of Al has six close P atoms, with no evidence of Al-O-Al bonds, showing that the connection between AlOn and PO4 is attained through corners. There is no evidence of local segregation of cationic species in the phosphate matrix. A definite precedence in the formation of Q2m units was found as the Al concentration is increased, consisting of the progressive conversion of Q20 to Q21 and then Q21 to Q22 units with increasing x. Up to intermediate values of x, the speciation shows an above-random trend compatible with a binary distribution {Q20,Q21} for the K-Al and Pb-Al systems.FAPESP (06/61218-0)DFG (SBF 458)CNPqCAPE

YPdSn and YPd2Sn: Structure, 89Y solid state NMR and 119Sn Mössbauer spectroscopy

The stannides YPdSn and YPd2Sn were synthesized by high-frequency melting of the elements in sealed tantalum tubes. Both structures were refined on the basis of single crystal X-ray diffractometer data: TiNiSi type, Pnma, a=715.4(1), b=458.8(1), c=789.1(1) pm, wR2=0.0461, 510 F2 values, 20 variables for YPdSn and MnCu2Al type, Fm3¯m, a=671.44(8), wR2=0.0740, 55 F2 values, 5 parameters for YPd2Sn. The yttrium atoms in the new stannide YPdSn are coordinated by two tilted Pd3Sn3 hexagons (ordered AlB2 superstructure). In the Heusler phase YPd2Sn each yttrium atom has octahedral tin coordination and additionally eight palladium neighbors. The cubic site symmetry of yttrium is reflected in the 119Sn Mössbauer spectrum which shows no quadrupole splitting. In contrast, YPdSn shows a single signal at δ=1.82(1) mm/s subjected to quadrupole splitting of ΔEQ=0.93(1) mm/s. Both compounds have been characterized by high-resolution 89Y solid state NMR spectroscopy, which indicates the presence of strong Knight shifts. The spectrum of YPd2Sn is characterized by an unusually large linewidth, suggesting the presence of a Knight shift distribution reflecting local disordering effects. The range of 89Y Knight shifts of several binary and ternary intermetallic yttrium compounds is briefly discussed.Deutsche Forschungsgemeinschaf

Structural and dynamic characterization of Li12Si7 and Li12Ge7 using solid state NMR

Local environments and lithium ion dynamics in the binary lithium silicide Li12Si7, and the analogous germanium compound have been characterized by detailed 6Li, 7Li, and 29Si variable temperature static and magic-angle spinning (MAS) NMR experiments. In the MAS-NMR spectra, individual lithium sites are generally well-resolved at temperatures below 200 K, whereas at higher temperatures partial site averaging is observed on the kHz timescale. The observed lithium chemical shift ranges of up to 60 ppm indicate a significant amount of electronic charge stored on the lithium species, consistent with the expectation of the extended Zintl–Klemm–Bussmann concept used for the theoretical description of lithium silicides. Furthermore the strongly diamagnetic chemical shifts observed for the lithium ions situated directly above the five-membered Si5 rings suggest the possibility of aromatic ring currents in these structural elements. This assignment is confirmed further by 29Si{7Li} CPMAS-heteronuclear correlation experiments. The 29Si MAS-NMR spectra of Li12Si7, aided by 2-D J-resolved spectroscopy, are well suited for differentiating between the individual sites within the silicon framework, while further detailed connectivity information is available on the basis of 2-D INADEQUATE and radio frequency driven recoupling (RFDR) spectra. Variable temperature static 7Li NMR spectra reveal the onset of strong motional narrowing effects, illustrating high lithium ionic mobilities in both of these compounds.DFG (Ec168/9-1

Mixed network former effect in ion-conducting Alkali borophosphate glasses: structure/property correlations in the system '['M IND. 2'O] IND. 1/3''['('B IND. 2''O IND. 3') IND. x''('P IND. 2''O IND. 5') IND. 1-x'] IND. 2/3' (M = 'LI', K, 'CS')

Glasses in the system '['M IND. 2'O] IND. 1/3''['('B IND. 2''O IND. 3') IND. x''('P IND. 2''O IND. 5') IND. 1-x'] IND. 2/3' (M = 'LI', K, 'CS') (0.0 'MENOR OU IGUAL' x 'MENOR OU IGUAL' 1.0) were prepared by standard melt-quenching procedures, and their physical properties were characterized by thermal analysis, density measurements, and impedance spectroscopy. Their atomic level structures were comprehensively characterized by Raman spectroscopy, by X-ray photoelectron spectroscopy (XPS), and by ' ANTPOT. 11 B', 'ANTPOT. 31 P', and 'ANTPOT. 7 LI' as well as 'ANTPOT. 133 CS' high resolution solid state magic-angle-spinning (MAS) NMR techniques. 'ANTPOT. 31 P' MAS NMR peak assignments were aided by the presence or absence of homonuclear indirect 'ANTPOT. 31 P'-'ANTPOT. 31 P' spin–spin interactions, "J-coupling", as detected via refocused INADEQUATE techniques. Consistent speciations of the phosphate and borate network former components in terms of the various 'P POT. n IND. mB' and 'B POT.n IND. mP' units, where n is the number of bridging oxygens (BOs) and m is the number of B or P units bonded to P or B, respectively, present in these glasses were derived from 'ANTPOT. 11 B' MAS NMR, combined with both 'ANTPOT. 31 P' MAS NMR and XPS line shape analyses, constrained by charge and mass balance considerations. The speciation of the BO species in the glassy network was quantified both by O 1s XPS and 'ANTPOT. 11 B'{'ANTPOT. 31 P'} rotational echo double resonance spectroscopy. Both experiments indicate a strong preference of heteroatomic B-O-P over homoatomic P-O-P and B-O-B linkages to the extent that close to the maximum number of possible 'B POT. 4'-O-P linkages is formed. Further, the structural speciations of the borate and phosphate species, together with bond valence (BV) analyses of the charge redistribution on the various structural units, indicate that the alkali network modifier oxide is not proportionally shared between the two network former components B and P in these systems. Rather, the amounts and types of the various borate and phosphate species are found to be consistent with the negative charge brought in by the alkali modifier 'M IND. 2'O being distributed more toward the phosphate structural units which are suggested to attract a larger concentration of network modifier species than predicted by the bulk composition. The experimental results obtained from these studies help in understanding the strongly nonlinear compositional dependence of the glass transition temperature and the ionic conductivity in terms of detailed atomic-level structural information. The emerging structural principles appear to be general to all of the alkali borophosphate glass systems, with the type of alkali ion network modifier producing only minor variations.Deutsche Forschungsgemeinschaft (SFB 458; Ionic Motion in Disordered Materials)National Science Foundation (DMR, Materials World Network NSFDMR 0701564

Structural, Physical, Theoretical and Spectroscopic Investigations of Mixed‐Valent Eu2Ni8Si3 and Its Structural Anti‐Type Sr2Pt3Al8

Eu2Ni8Si3 and its anti-type representative Sr2Pt3Al8 were synthesized from the elements. They crystallize in the tetragonal crystal system with space group P42/nmc and with lattice parameters of a=997.9(1) and c=747.6(1) pm (Eu2Ni8Si3) as well as a=1082.9(2) and c=823.3(2) pm (Sr2Pt3Al8). Both compounds were investigated via single crystal X-ray diffraction, indicating slight Si/Ni mixing for the silicide. Sr2Pt3Al8 exhibits a temperature independent magnetic susceptibility, suggesting superimposed dia- and Pauli-paramagnetic contributions. The independent Al and Pt sites of the platinide were further characterized by 27Al and 195Pt solid-state NMR spectroscopy, which were assigned with the help of electronic structure calculations. ICOHP calculations and Bader charges were used to analyze the bonding situation. Eu2Ni8Si3 in contrast is paramagnetic with a ferromagnetic transition at TC= 46.9(2) K and exhibits an effective magnetic moment of μeff= 6.61(1) μB per Eu atom. The latter is in line with an intermediate valence that was further proven by 151Eu Mößbauer spectroscopic investigations. At 300 K, the refined Eu2+/Eu3+ ratios are 60%/40%, at 78 K 62% and 38% (Eu2+/Eu3+) are observed, being in line with the ratio deduced from the magnetic susceptibility. Finally, at 6 K a ratio of 68% Eu2+ and 32% Eu3+ was observed. Below the Curie temperature, the Eu2+ signal shows a full magnetic hyperfine splitting, with an internal magnetic field value of B0=28.4 T