After the last damaging earthquake in 2012, an anti-seismic reinforcement project of the cathedral of Modena was designed giving us the opportunity to investigate and date the building materials. Radiocarbon (14C), optically stimulated luminescence (OSL), and thermoluminescence (TL) dating techniques were performed on the vaults with the aim to (1) clarify the construction timing, (2) define the history of the restorations, and (3) explore the possible correlation of the main restoration works to the earthquake chronology deduced from the historic catalog. Preliminary results show that medieval older bricks were reused for most of the original construction. Only lime and non-gypsum mortar was used for the original construction in the 15th century and for later repair of damage caused by earthquakes in the 16th and 17th centuries. Gypsum mortar was used for later repair in the 18th century. The results show much stronger damage due to earthquakes than previously thought.

A hollow γ-TNB turbine blade was 3D printed in this studying using the –R Optomec LENS machine from the elemental powders of aluminium, niobium and titanium making use of the laser “in situ” alloying approaching. The printed blade was characterised of a nearly lamellar β microstructure in the As-built state. The microstructure of the blade post heat treated was characterised of grain growth and coarsening and the formation of the γ phase which was of the result of the transformation of β. This transformation was also observed in the As-built state and is reported here for the first time. A massive crack that was observed half-way through in the built was attributed to the thermal shocks that are experienced by the almost immediately after manufacturing. The EDS and Map taken on the As-built and heat treated samples conclude that there was no segregation in the alloying element during manufacturing and that the blade was of the dual phase. Hardness results indicated the heat treated sample was 91 HV0.5 lower in hardness when compared to the As-built component. The successful print of this hollow blade indicate that γ-TNB and other Ti-Al alloys can be printed with the LENS but if a crack free sample was to be achieved the set-up had to be manipulated or addition resources must be added to adapt the set-up. Meanwhile the successes of this study show that LENS is going to be considered as a cost-effective manufacturing tool in the future for 3D printing Ti-Al and other metallic structure that would have improved properties when compared to traditional manufacturing technique such as casting and the powder bed systems.

Despite the improvements seen in efficiency of GaAs cells over the years, there remains room for improvement for it to approach the theoretical single junction limit posited by Shockley and Quiesser decades ago. One of the more pursued options is the growth of quantum wells within the structure of GaAs to enhance its photon absorption below its bandgap. Multiple Quantum Wells (MQW) have been an ongoing topic of research and discussion for the scientific community with structures like InGaAs/GaAs and InGaP/GaAs quantum wells producing promising results that could potentially improve overall energy conversion. Here, we used WEIN2K, a commercial density functional theory package, to study the ternary compound Ga1-xTlxAs and determine its electronic properties. Using these results combined with experimental confirmation we extend these properties to simulate its application to form a MQW GaAs/ Ga1-xTlxAs solar cell. Ga1-xTlxAs is a tunable ternary compound, with its bandgap being strongly dependent on the concentration of Tl present. Concentrations of Tl as low as 7% can reduce the bandgap of Ga1-xTlxAs to roughly 1.30 eV from GaAs’s 1.45 eV at room temperature with as little as a 1.7% increase in lattice constant. The change in bandgap, accompanied by the relatively small change in lattice constant makes Ga1-xTlxAs a strong candidate for a MQW cell with little to no strain balancing required within the structure to minimize unwanted defects that impede charge collection within the device. Our GaAs photodiode with TlGaAs MQWs shows an expanded absorption band and improved conversion efficiency over the standard GaAs photovoltaic cell with dilute concentrations of Tl incorporated into the compound.

TlBr crystals have superior radiation detection properties; however, their properties degrade in the range of hours to weeks when an operating electrical field is applied. To account for this rapid degradation using the widely-accepted vacancy migration mechanism, the vacancy concentration must be orders of magnitude higher than any conventional estimates. The present work has incorporated a new analytical variable charge model in molecular dynamics (MD) simulations to examine the structural changes of materials under electrical fields. Our simulations indicate that dislocations in TlBr move under electrical fields. This discovery can lead to new understanding of TlBr aging mechanisms under external fields.

Bi2Te2Se (BTS221) bulk crystals were recently discovered as an intrinsic 3D topological insulator. We have synthesized this material, and studied the transport properties of BTS221 from the thermoelectrics perspective. Temperature (T) dependent resistivity measurement indicates surface dominant transports in our sample at low T. We also report Seebeck measurement between 50K to room T.

Ternary thallium chalcogenides of the formula Tl4MQ4, where M = Zr and Hf and Q = S, Se, and Te were synthesized and characterized. Our X-ray diffraction studies on suitable single crystals reveal that the sulphides and selenides are isostructural, with monoclinic space group P, whereas the corresponding tellurides crystallize in the rhombohedral crystal system (R). The structures of the sulphides and selenides are comprised of zigzag chains of edge-sharing MQ6 octahedra, whereas the MTe6 octahedra are interconnected via common faces to form linear trimeric units. In all cases, the atoms adopt common oxidation states, namely Tl+, M4+, and Q2–. The electronic structure calculations using the linear muffin tin orbital (LMTO) method predicted band gaps of 1.7 eV, 1.3 eV and 0.3 eV for the sulphides, selenides and tellurides, respectively, implying sulphides and selenides are large band gap materials, and the tellurides narrow gap semiconductors. Their electronic transport properties are also evaluated with respect to the thermoelectric energy conversion.

The scaling of contemporary metal-insulator-metal (MIM) capacitors requires oxides of higher dielectric constant (>10), such as hafnium oxide (∼18) and titanium oxide (∼40). Intensive research of these oxides and oxide stacks is needed to develop them into high quality electronic materials for their application as capacitors in high temperature environments. High-k dielectrics such as HfO2 and HfO2/TiO2/HfO2 have been grown by thermal oxidation to fabricate MIM capacitors on SiO2/Si substrates and on sapphire substrates also. The thermally grown Al/HfO2/TiO2/HfO2/Pt/Ti/SiO2/Si MIM capacitor is reported here for the first time. The MIM capacitor using HfO2/TiO2/HfO2 dielectric film shows a similar frequency dependence using HfO2 dielectric on a SiO2/Si substrate, whilst its voltage linearity coefficients, leakage current and temperature coefficient are higher than the capacitor employing HfO2 dielectric. The MIM capacitor with HfO2 dielectric fabricated on sapphire substrate shows the strongest frequency dependence, voltage linearity coefficient and temperature dependence which is related to the surface roughness of substrate. The high capacitance density of these capacitors, ranging from 5.21 fF/µm2, meets the ITRS requirements for analog capacitor up to 2012. The MIM capacitor using 30nm HfO2 dielectric film illustrates highest capacitance density, 5.21 fF/µm2, a VCC of 236 ppm/V2, a temperature coefficient of 290 ppm/ºC, measured up to 300 ºC, and leakage current density which is 1.3 × 10−7 A/cm2 at 1V.

With the goal of developing high-performance bulk thermoelectric materials, we have characterized ternary silver thallium tellurides. The ternary silver thallium tellurides exhibit extremely low thermal conductivity (<0.5 Wm−1K−1) and consequently their thermoelectric performance is excellent. Although the extremely low thermal conductivity materials, as typified by the ternary silver thallium tellurides, would be a new class of next-generation thermoelectric materials, thallium compounds are unsuitable for practical application because of their toxicity. Against such a background, we are currently exploring thallium-free thermoelectric materials with extremely low thermal conductivity. In this paper, we will briefly summarize the thermoelectric properties of ternary thallium tellurides obtained in our group. Further experiments aimed at improving the ZT of these materials will be presented. Finally, we will propose two candidates: Ag8GeTe6 and Ga2Te3 as thallium-free low thermal conductivity materials.

Polycrystalline-sintered samples of thallium based substances, (Tl2Te)100−x(Sb2Te3)x (x= 0, 1, 5, 10), were prepared by melting Tl2Te and Sb2Te3 ingots followed by annealing in sealed quartz ampoules. The thermoelectric properties were measured from room temperature to around 600 K. The values of the Seebeck coefficient of all samples are positive, indicating a p-type conduction characteristic. The maximum value of the power factor is 6.53×10−4 Wm−1K−2 at 591 K obtained for x= 10 (Tl9SbTe6), which is about one order lower than those of state-of-the-art thermoelectric materials. All samples indicate an extremely low thermal conductivity, for example that of Tl2Te is approximately 0.35 Wm−1K−1 from room temperature to around 600 K. Although the electrical performance of the samples is not so good, the ZT value is relatively high due to the extremely low thermal conductivity. The maximum ZT value is 0.42 at 591 K obtained for Tl9SbTe6.

We have studied the thermoelectric properties of thallium compounds as novel thermoelectric materials. Especially, we focus on the Ag-Tl-Te ternary system, in which we found that Ag9TlTe5 exhibits an excellent thermoelectric figure of merit (ZT= 1.23) because of its extremely low thermal conductivity (around 0.22 Wm−1K−1). In this paper, we studied the thermal conductivity of four kinds of ternary silver thallium tellurides: AgTl3Te2, AgTlTe, Ag8Tl2Te5 and Ag9TlTe5, for which we found room temperature values of 0.39, 0.26, 0.14 and 0.21 Wm−1K−1, respectively. In order to understand the extremely low thermal conductivity, we performed an ultrasonic pulse echo measurement and evaluated some thermophysical properties.

We have prepared polycrystalline bulk samples of various thallium compounds and measured their thermoelectric properties. The most remarkable point of the thermoelectric properties of the thallium compounds is the extremely low thermal conductivity. The state-of-the-art thermoelectric materials such as Bi2Te3 and TAGS materials indicate relatively low the thermal conductivity, around 1.5 W/m/K. However, the thermal conductivity of the thallium compounds is below 0.5 W/m/K; especially that of silver thallium tellurides is around 0.25 W/m/K at room temperature. This extremely low thermal conductivity leads a great advantage for an enhancement of the thermoelectric performance. In this paper, we report on the properties of some thallium compounds selected for study as novel thermoelectric materials. One of these compounds seems to have a thermoelectric figure of merit comparable to those of state-of-the-art materials.