Zwanziger, Josef W.
Permanent URI for this collectionhttps://hdl.handle.net/10222/27756
Josef W. Zwanziger
Professor
Canada Research Chair, Tier I: NMR Studies of materials
Email: jzwanzig@dal.ca
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Item Open Access Thermal, vibrational, and thermoelastic properties of Y2Mo3O12 and their relations to negative thermal expansion(American Physical Society, 2014-07-21) Romao, Carl; Miller, Kimberley; Johnson, Michel; Zwanziger, Josef; Marinkovic, Bojan; White, Mary AnneY2 Mo3O12, a material that exhibits negative thermal expansion (NTE) from 10 to 1173 K, offers an excellent opportunity to examine relationships between NTE and other physical properties over a wide temperature range. We report experimental heat capacity, thermal conductivity, and elastic properties of Y2Mo3O12, as well as results of an ab initio study of the lattice dynamics, and show how the anomalously high heat capacity and low thermal conductivity are correlated with NTE. We also report the ab initio elastic tensor and experimental velocity of sound of Y2Mo3O12 and use it to calculate the thermal stresses in a simulated polycrystal using finite-element analysis, showing that elastic anisotropy and thermal expansion anisotropy couple to influence the properties of the bulk solid.Item Open Access The heat capacities of thermomiotic ScF3 and ScF3–YF3 solid solutions(Springer, 2015-05-01) Romao, Carl; Morelock, Cody; Johnson, Michel; Zwanziger, Josef; Wilkinson, Angus; White, Mary AnneScandium trifluoride (ScF3) exists in a cubic ReO3 structure that exhibits negative thermal expansion from 10 to 1100 K, while substituted Sc1−x Y x F3 materials display the same behavior at room temperature but transition into positive thermal expansion rhombohedral phases upon cooling. We have measured the heat capacity of ScF3 from 0.4 to 390 K and found no evidence of a phase transition, but do find that its low-temperature heat capacity is anomalously high. The heat capacities of substituted Sc1−x Y x F3 materials are also reported and show evidence of the cubic-rhombohedral phase transition for x ≥ 0.1 and smaller anomalies in the low-temperature heat capacity of the positive thermal expansion rhombohedral phases. To aid in interpretation of these results, the heat capacity of ScF3 was calculated from its phononic structure using density functional theory.Item Open Access Zero Thermal Expansion in ZrMgMo3O12: NMR Crystallography Reveals Origins of Thermoelastic Properties(American Chemical Society, 2015-03-23) Romao, Carl; Perras, Fred; Werner-Zwanziger, Ulrike; Lussier, Joey; Miller, Kimberley; Calahoo, Courtney; Zwanziger, Josef; Bieringer, Mario; Marinkovic, Bojan; Bryce, David; White, Mary AnneThe coefficient of thermal expansion of ZrMgMo3O12 has been measured and was found to be extremely close to zero over a wide temperature range including room temperature ( = (1.6 ± 0.2) × 10–7 K–1 from 25 to 450 °C by X-ray diffraction (XRD)). ZrMgMo3O12 belongs to the family of AMgM3O12 materials, for which coefficients of thermal expansion have previously been reported to range from low-positive to low-negative. However, the low thermal expansion property had not previously been explained because atomic position information was not available for any members of this family of materials. We determined the structure of ZrMgMo3O12 by nuclear magnetic resonance (NMR) crystallography, using 91Zr, 25Mg, 95Mo, and 17O magic angle spinning (MAS) and 17O multiple quantum MAS (MQMAS) NMR in conjunction with XRD and density functional theory calculations. The resulting structure was of sufficient detail that the observed zero thermal expansion could be explained using quantitative measures of the properties of the coordination polyhedra. We also found that ZrMgMo3O12 shows significant ionic conductivity, a property that is also related to its structure.Item Open Access Temperature dependent lattice misfit and coherency of Al3X (X = Sc, Zr, Ti and Nb) particles in an Al matrix(Elsevier, 2015-05-01) Saha, Saumitra; Todorova, Tsanka; Zwanziger, JosefThe lattice coherency and critical radii for Al3X precipitates in an aluminum matrix were computed using first-principles methods. From density functional perturbation theory and the quasi-harmonic approximation, the unit cell parameters as a function of temperature were determined for Al3Sc, Al3Zr, Al3Ti, and Al3Nb in the L12 structure, and for Al3Ti and Al3Nb in their more stable DO22 structures. From these data the lattice misfit and critical radii were determined. It was found that Al3Sc and Al3Zr behave similarly, with increasing critical radii and decreasing misfit as a function of temperature, while Al3Ti and Al3Nb behaved oppositely. Furthermore, the DO22 phases showed uniformly poor lattice coherence and very small critical radii. Superior alloy properties in Al/Al3X systems are suggested to require stabilization of the L12 phase in the precipitated particles.Item Open Access Topological constraints and the Makishima–Mackenzie model(Elsevier, 2015-12-01) Plucinski, Michal; Zwanziger, JosefComputations of the elastic properties of networks with bond stretch and bond angle bend forces are carried out in order to study their behavior as a function of average coordination number. It is found that the elastic constants essentially vanish as the average coordination number drops to 2.4. It is argued this phenomenon is responsible for the failure of the Makishima–Mackenzie model to predict accurately the elastic properties of borate glass, originating with B2O3 itself which also has an average coordination number of 2.4. Finally, a new model is proposed, similar to the Makishima–Mackenzie model but including explicitly the dependence on network connectivity.Item Open Access Relating 139La Quadrupolar Coupling Constants to Polyhedral Distortion in Crystalline Structures(American Chemical Society, 2015-10-26) Paterson, Alexander L; Hanson, Margaret; Werner-Zwanziger, Ulrike; Zwanziger, JosefA broad series of crystalline lanthanum oxide-based materials has been investigated through high-field 139La solid state nuclear magnetic resonance (ssNMR) spectroscopy and ab initio density functional theory (DFT) calculations. The 139La NMR spectra of LaBGeO5, LaBSiO5, LaBO3, LaPO4·1.8H2O, La2(SO4)3·9H2O, and La2(CO3)3·8H2O are reported for the first time. Both newly reported and literature values of 139La quadrupolar coupling constants (CQ) are related to various quantitative expressions of polyhedral distortion, including sphericity (Σ) and ellipsoid span (ϵ). The compounds were separated into two groups based upon their polyhedral distortion behavior: compounds with the general formula LaMO3, where M is a trivalent cation; compounds with different general formulas. The 139La CQ of the LaMO3 family was found to correlate best with ϵ. The 139La CQ of non-LaMO3 compounds correlates adequately to ϵ but is better described by Σ. The 139La isotropic chemical shift (δisoCS) of the non-LaMO3 compounds is negatively correlated with the lanthanum coordination number; there is insufficient data from the LaMO3 compounds to draw conclusions relating to chemical shift. DFT calculations of NMR parameters prove to be a sensitive probe of the quality of input geometry, with predicted parameters agreeing with experiment except in cases where the crystal structure is suspect.Item Open Access Designing glass with non-dispersive stress-optic response(Elsevier, 2016-02-01) Galbraith, Justine; Zwanziger, Josef WThe dispersion of the stress-optic response of a series of barium and lead phosphate glasses is measured using an ellipsometric method. It is found that the barium glasses display consistently positive dispersion with decreasing wavelength, while the lead glasses display consistently negative dispersion. It is found that the dispersion is roughly additive so that in mixed barium/lead phosphates, a composition may be found for which the dispersion is essentially zero across the optical range. The dispersion itself is shown to correlate with glass structure, giving an empirical relationship between stress-optic dispersion and composition. These results thus suggest a design rule for controlling stress-optic response in glass as a function of wavelength.Item Open Access Nanoindentation Study of the Surface of Ion-Exchanged Lithium Silicate Glass(American Chemical Society, 2016-02-25) Calahoo, Courtney; Zhang, Xiaofang; Zwanziger, Josef WVariations in mechanical properties (stiffness and hardness) were measured as a function of case depth in ion-exchange glasses using nanoindentation. A simple silicate composition, 30Li2O–70Si2O, was exchanged (Li+ ↔ K+) at several different temperatures, below and above the glass transition, to evaluate the effect of exchange temperature on mechanical properties throughout the ion-exchange layer. Significant enhancements in Young’s modulus and hardness were found near the edge in ion-exchanged glasses and attributed to compressive stress and the mixed-alkali effect. Indent size effect-like behaviors were observed in the untreated and ion-exchange samples alike near the sample edge; this was explained by surface-condition sensitivity and compressive stress found within this region. The elastic recovery and resistance to plastic deformation were calculated to assess the effect of ion exchange on elastic and plastic mechanical responses. Microhardness measurements of the exchanged samples were also made for comparison.Item Open Access Mechanical–Structural Investigation of Ion-Exchanged Lithium Silicate Glass using Micro-Raman Spectroscopy(American Chemical Society, 2016-03-21) Calahoo, Courtney; Zwanziger, Josef W; Butler, Ian SMicro-Raman spectroscopy was used to determine the structural modifications occurring in a simple ion-exchanged glass. The base lithium silicate composition 30Li2O–70SiO2 was studied as it underwent ion exchange, Li+ ↔ K+, at six temperatures spanning the glass transition point. Using a well-developed relationship between the Si–O–Si bond angle, the Si–O bond length, and Raman shifts, the reduction in network molar volume and increase in compressive stress were estimated. On the basis of the effect of the ion-exchange temperature, the existence of a threshold energy below which the compressive stress manifests as the reorientation of silica tetrahedra only and above which the system relaxes by increasing the Si–O bond length is proposed. Finally, the linear network dilation coefficient is revisited in terms of these new data and an explanation given for its underestimation and overestimation of stress at low and high temperatures, respectively.Item Open Access Measuring the Geometric Component of the Transition-Probability in a 2-Level System(1991-04) ZWANZIGER, JW; RUCKER, SP; CHINGAS, GCWe describe the measurement of a component of the nonadiabatic transition probability in a two-level system that depends only on the path through parameter space followed by the Hamiltonian, and not on how fast the path is traversed [M. V. Berry, Proc. R. Soc. London 430, 405 (1990)]. We performed the measurement by sweeping a radio-frequency field through the Zeeman resonance of carbon-13 in a static magnetic field and measuring the transition probability P at the end of each sweep. We found that, for appropriately chosen radio-frequency sweep forms, a factor of P is independent of the duration of the sweep, in accordance with the theory of Berry.Item Open Access Structure and Disorder of Phosphates in Ag2o-Agi-P2o5 Glasses(1993-06) ZWANZIGER, JW; OLSEN, KK; TAGG, SLWe directly probe the microstructure of the different phosphates in several glasses in the Ag2O-AgI-P2O5 system, by means of variable angle correlation NMR spectroscopy. This two-dimensional experiment separates the chemical-shift powder patterns of the phosphorus sites according to their isotropic chemical shifts. We have thus determined all chemical-shift tensor elements for each chemically distinct phosphorus site in these glasses, and their variation within each site. Our results yield a precise description of the phosphate types and geometries in these glasses.Item Open Access Sodium distribution in sodium tellurite glasses probed with spin-echo NMR(1997-09) Zwanziger, JW; McLaughlin, JC; Tagg, SLWe present results on the spatial distribution of sodium cations in sodium tellurite glasses as a function of sodium oxide content, obtained using a spin-echo NMR experiment. Glasses were studied with sodium oxide content ranging from 10 to 30 mol %. From the decay rate of the spin echo we infer the proximity of sodium nuclei at each composition. We found that at low sodium oxide contents the data are well modeled by a random distribution of sodium ions, with a closest approach distance of 3.2 Angstrom in correspondence with sodium tellurite crystal structures. At higher sodium oxide contents, however, the data agree with sodium distributions that have extensive intermediate range order, on length scales of at least 10 Angstrom. This ordering is most pronounced at 20% sodium oxide content, the composition at which this glass has been claimed to have maximum stability against devitrification.Item Open Access First-principles study of the nuclear quadrupole resonance parameters and orbital ordering in LaTiO3.(2009) Zwanziger, J. W.The electronic structure of the distorted perovskite LaTiO3 is studied using d.-functional theory, implemented with a projector-augmented wave formalism together with the local-d. approxn. plus Hubbard U-parameter (LDA+U) model. Various exptl. detd. quantities, including the antiferromagnetic ordering and spin moments and elec. field gradients at the lanthanum and titanium sites, are well reproduced. It is found that the excess spin d. on the titanium sites, which accounts for the antiferromagnetism, is very well described by the conjectured dxy+dyz+dzx orbital configuration.Item Open Access Phonon dispersion and Gruneisen parameters of zinc dicyanide and cadmium dicyanide from first principles: Origin of negative thermal expansion.(2007) Zwanziger, J. W.Zinc dicyanide, Zn(CN)2, and the isostructural cadmium dicyanide show neg. thermal expansion over a broad range of temps. By the use of d. functional theory calcns., we det. the phonon dispersion curves of these materials and show that the transverse acoustic modes give rise to a relatively sharp feature at about 2-4 meV in the phonon d. of states. In addn., we compute the Gruneisen parameters of these modes and show that they have large neg. values, indicating that they are the primary contributors to the neg. thermal expansion in this material. Our results are in broad agreement with recent neutron scattering expts. on Zn(CN)2 and the rigid unit mode anal. of these materials.Item Open Access Non-Abelian Effects in a Quadrupole System Rotating Around 2 Axes(1990-09) ZWANZIGER, JW; KOENIG, M.; PINES, A.No abstract available.Item Open Access Density-operator theory of orbital magnetic susceptibility in periodic insulators(2011-08) Gonze, X.; Zwanziger, J. W.The theoretical treatment of homogeneous static magnetic fields in periodic systems is challenging, as the corresponding vector potential breaks the translational invariance of the Hamiltonian. Based on density operators and perturbation theory, we propose for insulators a periodic framework for the treatment of magnetic fields up to arbitrary order of perturbation, similar to widely used schemes for electric fields. The second-order term delivers a new, remarkably simple formulation of the macroscopic orbital magnetic susceptibility for periodic insulators. We validate the latter expression using a tight-binding model, analytically from the present theory and numerically from the large-size limit of a finite cluster, with excellent numerical agreement.Item Open Access Fractional Quantization of Molecular Pseudorotation in Na-3(1986-06) DELACRETAZ, G.; GRANT, ER; WHETTEN, RL; WOSTE, L.; ZWANZIGER, JWNo abstract available.