Mary Anne White

Properties of Materials

PART I: INTRODUCTION 1. Materials Science PART II: COLOUR AND OTHER OPTICAL PROPERTIES OF MATTER PART III: THERMAL PROPERTIES OF MATERIALS PART IV: ELECTRICAL AND MAGNETIC PROPERTIES OF MATTER PART V: MECHANICAL PROPERTIES OF MATERIALS Appendix 1: Fundamental Physical Constants Appendix 2: Unit Conversions Appendix 3: The 14 Three-Dimensional Lattice Types Appendix 4: The Greek Alphabet Appendic 5: Sources for Lecture Demonstration Materials

Dye–developer interactions in the crystal violet lactone–lauryl gallate binary system: implications for thermochromism

Multicomponent thermochromic systems have potential applications in rewritable printing materials. A hindrance to the widespread application of these materials is a lack of detailed knowledge of the intermolecular interactions within the systems. In this study, dye–developer interactions from a typical three-component (dye/developer/solvent) thermochromic system are examined. The stoichiometries of stable and metastable dye–developer complexes formed are examined and thermodynamic interaction potentials are determined. The colour-forming interaction and its importance to the understanding of thermochromic multicomponent systems are discussed.

Temperature Dependence of Thermal Conductivity Enhancement in Single-walled Carbon Nanotube/polystyrene Composites

The thermal conductivity of single-walled carbon nanotube (SWCNT)/polystyrene composites, prepared by a method known to produce a uniform distribution of SWCNT bundles on the micrometer length scale, was measured in the temperature range from approximately 140 to 360 K. The thermal conductivity enhancement (50% for 1 mass % at 300 K) is reasonably constant above room temperature but is reduced at the lower temperatures. This result is consistent with the expected, large contribution of interfacial thermal resistance in SWCNT/polymer composites. Enhancements in electrical conductivity show that 1 mass % loading is in the region of the electrical percolation threshold.

Competition between dye–developer and solvent–developer interactions in a reversible thermochromic system

Multicomponent thermochromic systems contain a dye, a colour developer, and a solvent. Dye–developer interactions, including complex formation, have been examined in our previous study. In this paper, the interactions between the same developer (lauryl gallate) and a solvent (1-octadecanol) are characterised both through phase diagram determination and from Raman spectroscopy. The role of dye–developer complex formation in the thermochromic behaviour of the ternary thermochromic system (with the addition of crystal violet lactone dye) is addressed. We find two competing interactions for the developer: the dye–developer complex forms in the melt and in the quenched solid (giving a coloured mixture), but a solvent–developer complex is more favorable as the solid equilibrates. The latter gives rise to concomitant decolourisation.

Thermal properties of zeolites: effective thermal conductivity of dehydrated powdered zeolite 4A

The determination of the subambient effective thermal conductivity of evacuated powdered zeolite 4A is described. The results are modelled successfully in terms of boundary scattering, point defects and three-phonon Umklapp processes.

Computational and experimental investigation of TmAgTe2 and XYZ2 compounds, a new group of thermoelectric materials identified by first- principles high-throughput screening†

A new group of thermoelectric materials, trigonal and tetragonal XYZ2 (X, Y: rare earth or transition metals, Z: group VI elements), the prototype of which is TmAgTe2, is identified by means of high-throughput computational screening and experiment. Based on density functional theory calculations, this group of materials is predicted to attain high zT (i.e. B1.8 for p-type trigonal TmAgTe2 at 600 K). Among approximately 500 chemical variants of XYZ2 explored, many candidates with good stability and favorable electronic band structures (with high band degeneracy leading to high power factor) are presented. Trigonal TmAgTe2 has been synthesized and exhibits an extremely low measured thermal conductivity of 0.2–0.3 W m � 1 K � 1 for T 4 600 K. The zT value achieved thus far for p-type trigonal TmAgTe2 is approximately 0.35, and is limited by a low hole concentration (B10 17 cm � 3 at room temperature). Defect calculations indicate that TmAg antisite defects are very likely to form and act as hole killers. Further defect engineering to reduce such XY antisites is deemed important to optimize the zT value of the p-type TmAgTe2.

Understanding thermoelectric properties from high-throughput calculations: trends, insights, and comparisons with experiment

We present an overview and preliminary analysis of computed thermoelectric properties for more than 48 000 inorganic compounds from the Materials Project (MP). We compare our calculations with available experimental data to evaluate the accuracy of different approximations in predicting thermoelectric properties. We observe fair agreement between experiment and computation for the maximum Seebeck coefficient determined with MP band structures and the BoltzTraP code under a constant relaxation time approximation (R2 = 0.79). We additionally find that scissoring the band gap to the experimental value improves the agreement. We find that power factors calculated with a constant and universal relaxation time approximation show much poorer agreement with experiment (R2 = 0.33). We test two minimum thermal conductivity models (Clarke and Cahill–Pohl), finding that both these models reproduce measured values fairly accurately (R2 = 0.82) using parameters obtained from computation. Additionally, we analyze this data set to gain broad insights into the effects of chemistry, crystal structure, and electronic structure on thermoelectric properties. For example, our computations indicate that oxide band structures tend to produce lower power factors than those of sulfides, selenides, and tellurides, even under the same doping and relaxation time constraints. We also list families of compounds identified to possess high valley degeneracies. Finally, we present a clustering analysis of our results. We expect that these studies should help guide and assess future high-throughput computational screening studies of thermoelectric materials.

Temperature excursions at the pulp-dentin junction during the curing of light-activated dental restorations

OBJECTIVES Excessive heat produced during the curing of light-activated dental restorations may injure the dental pulp. The maximum temperature excursion at the pulp-dentin junction provides a means to assess the risk of thermal injury. In this investigation we develop and evaluate a model to simulate temperature increases during light-curing of dental restorations and use it to investigate the influence of several factors on the maximum temperature excursion along the pulp-dentin junction. METHODS Finite element method modeling, using COMSOL 3.3a, was employed to simulate temperature distributions in a 2D, axisymmetric model tooth. The necessary parameters were determined from a combination of literature reports and our measurements of enthalpy of polymerization, heat capacity, density, thermal conductivity and reflectance for several dental composites. Results of the model were validated using in vitro experiments. RESULTS Comparisons with in vitro experiments indicate that the model provides a good approximation of the actual temperature increases. The intensity of the curing light, the curing time and the enthalpy of polymerization of the resin composite were the most important factors. The composite is a good insulator and the greatest risk occurs when using the light to cure the thin layer of bonding resin or in deep restorations that do not have a liner to act as a thermal barrier. SIGNIFICANCE The results show the importance of considering temperature increases when developing curing protocols. Furthermore, we suggest methods to minimize the temperature increase and hence the risk of thermal injury. The physical properties measured for several commercial composites may be useful in other studies.

Spin Waves and Quantum Criticality in the Frustrated XY Pyrochlore Antiferromagnet Er2Ti2O7

We report detailed measurements of the low temperature magnetic phase diagram of Er2Ti2O7. Heat capacity and time-of-flight neutron scattering studies of single crystals reveal unconventional low-energy states. Er3+ magnetic ions reside on a pyrochlore lattice in Er2Ti2O7, where local XY anisotropy and antiferromagnetic interactions give rise to a unique frustrated system. In zero field, the ground state exhibits coexisting short and long-range order, accompanied by soft collective spin excitations previously believed to be absent. The application of finite magnetic fields tunes the ground state continuously through a landscape of noncollinear phases, divided by a zero temperature phase transition at micro{0}H{c} approximately 1.5 T. The characteristic energy scale for spin fluctuations is seen to vanish at the critical point, as expected for a second order quantum phase transition driven by quantum fluctuations.

Automated, small sample‐size adiabatic calorimeter

An automated adiabatic calorimeter with an internal volume of 5 cm3, operable over the temperature range from 30 to 380 K is described. One of the main advantages of this calorimeter over others in use is the much abbreviated down time during sample changes, due to interchangeable sample vessels that fit into the heater/thermometer assembly. This calorimeter was tested by measuring the heat capacity of benzoic acid, and the results agreed with the literature values to within 0.5%.