Zwanziger, Josef W.
http://hdl.handle.net/10222/27756
2022-09-29T11:31:19ZThermal, vibrational, and thermoelastic properties of Y2Mo3O12 and their relations to negative thermal expansion
http://hdl.handle.net/10222/71505
Thermal, vibrational, and thermoelastic properties of Y2Mo3O12 and their relations to negative thermal expansion
Romao, Carl; Miller, Kimberley; Johnson, Michel; Zwanziger, Josef; Marinkovic, Bojan; White, Mary Anne
Y2 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.
2014-07-21T00:00:00ZThe heat capacities of thermomiotic ScF3 and ScF3–YF3 solid solutions
http://hdl.handle.net/10222/71504
The heat capacities of thermomiotic ScF3 and ScF3–YF3 solid solutions
Romao, Carl; Morelock, Cody; Johnson, Michel; Zwanziger, Josef; Wilkinson, Angus; White, Mary Anne
Scandium 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.
2015-05-01T00:00:00ZZero Thermal Expansion in ZrMgMo3O12: NMR Crystallography Reveals Origins of Thermoelastic Properties
http://hdl.handle.net/10222/71503
Zero Thermal Expansion in ZrMgMo3O12: NMR Crystallography Reveals Origins of Thermoelastic Properties
Romao, Carl; Perras, Fred; Werner-Zwanziger, Ulrike; Lussier, Joey; Miller, Kimberley; Calahoo, Courtney; Zwanziger, Josef; Bieringer, Mario; Marinkovic, Bojan; Bryce, David; White, Mary Anne
The 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.
2015-03-23T00:00:00ZTemperature dependent lattice misfit and coherency of Al3X (X = Sc, Zr, Ti and Nb) particles in an Al matrix
http://hdl.handle.net/10222/71491
Temperature dependent lattice misfit and coherency of Al3X (X = Sc, Zr, Ti and Nb) particles in an Al matrix
Saha, Saumitra; Todorova, Tsanka; Zwanziger, Josef
The 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.
2015-05-01T00:00:00Z