We report on the temperature dependence of thermal conductivity of single crystalline and polycrystalline organometallic perovskite CH3NH3PbI3. The comparable absolute values and temperature dependence of the two samples’ morphologies indicate the minor role of the grain boundaries on the heat transport. Theoretical modeling demonstrates the importance of the resonant scattering in both specimens. The interaction between phonon waves and rotational degrees of freedom of CH3NH3 + sublattice emerges as the dominant mechanism for attenuation of heat transport and for ultralow thermal conductivity of 0.5 W/(Km) at room temperature.

Oxygen vacancies created in anatase TiO2 by UV photons (80 -130 eV) provide an effective electrondoping mechanism and induce a hitherto unobserved dispersive metallic state. Angle resolved photoemission (ARPES) reveals that the quasiparticles are large polarons. These results indicate that anatase can be tuned from an insulator to a polaron gas to a weakly correlated metal as a function of doping and clarify the nature of conductivity in this material.The anatase structural phase of titanium dioxide (TiO 2 ) can be the key element in novel applications. Whereas extensive work has been focused on its famous photocatalytic behavior [1-3], more and more proposed devices, such as memristors [4], spintronic devices [5], and photovoltaic cells [6][7][8], rely on its less well-known electronic properties. In particular, anatase has been recently suggested as a candidate for replacing the In-based technology for transparent conducting oxides [9] in a wide range of applications from solar cell elements, to light-emitting devices, to flat panels, to touch-screen controls [10]. The crucial quantity for the figure of merit in these devices is conductivity, and it is therefore of major interest to understand and control the electronic properties of pristine and doped anatase.Stoichiometric anatase is an insulator with a 3.2 eV band gap [11] but oxygen vacancies, typically present with concentrations in the 10 17 cm −3 range [12,13], create a shallow donor level ∼10 meV below the conduction band (CB) [14]. Since large single crystals became available for transport studies, a better insight has been gained on the influence of these donors on the electronic response of anatase. Above ∼60 K, the electrons thermally excited into the CB give rise to metallic-like transport. At lower temperatures, the anomalous increase of resistivity indicates that the charge carriers are not bare electrons but polarons [14], i.e., electrons coherently coupled to a lattice distorsion induced by the Coulomb interaction. Understanding the properties of such composite particles in anatase is important to better engineer the material for targeted applications, where the low electron mobility often represents the overall performance bottleneck. We will also demonstrate that, from the point of view of fundamental physics, anatase represents an excellent model compound to study the behavior of the "rare" large polaron quasiparticles (QPs), intermediate between localized small polarons and free electrons.We performed ARPES measurements on TiO 2 single crystals ( Fig. 1(a)) and thin films grown in situ on insulating LaAlO 3 and conducting Nb-doped SrTiO 3 substrates. Clean (001) surfaces were prepared as described in Suppl. Inf. The results presented have been obtained consistently both for single crystals and thin films, and therefore reflect intrinsic properties of the anatase phase, independent of the sample preparation method. While oxygen defects are always present to some extent after the surface preparation, we have found that exposure to UV photons...

The hybrid halide perovskites, the very performant compounds in photovoltaic applications, possess large Seebeck coefficient and low thermal conductivity making them potentially interesting high figure of merit (ZT) materials. For this purpose one needs to tune the electrical conductivity of these semiconductors to higher values. We have studied the CH3NH3MI3 (M=Pb,Sn) samples in pristine form showing very low ZT values for both materials; however, photoinduced doping (in M=Pb) and chemical doping (in M=Sn) indicate that, by further doping optimization, ZT can be enhanced toward unity and reach the performance level of the presently most efficient thermoelectric materials.X. Mettan et al. 04.26.2015 1

Three dimensional printing enables realization of complex shape rare earth permanent magnet that enable unlocking the full potential of electrical devices for energy consumption and renewable energy production.

Single crystals of Mo and Ta dichalcogenides, MX2 (M = Mo, Ta and X = S, Se, Te), have been grown by the chemical vapor transport method using a novel transport reaction that involves a mixture of M, MCl5 and X as a source. The article reports the details of the growth method and the characterization of the single crystals

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Anatase is a T iO 2 polymorph which is a 3.2 eV gap semiconductor interesting for several applications, including catalysis, photocatalysis, and, especially, dye-sensitized solar cells. Surprisingly, transparent single crystals of anatase grown in our laboratory show a metallic resistivity above 60 K which origin is a shallow donor level created by oxygen vacancies. The high value of the resistivity and its T 3 temperature dependence are the result of the polaronic nature of the charge carriers which is supported by the Seebeck coefficient (S). The application of hydrostatic pressure fails to close the donor level and to extend the conducting state to the entire temperature range. Instead, we have found a non-monotonic variation of the low temperature activation energy with applied pressure which is ascribed to the change of polaron's mobility. Thermo-electric power exhibits an unconventional temperature and pressure dependence shedding an additional light on the conductivity mechanism in this compound. The pressure dependence of S is governed by the transport of the large entropy associated with the polaron formation.

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