Understanding the origin of the strong difference of electrical parameters between as grown and annealed undoped ZnO films prepared at a temperature range of 100–200 °C by thermal atomic layer deposition is essential for their future applications. In this paper, we show that the conductivity drop by up to 4 orders of magnitude as effect of post-growth annealing is accompanied by multiple simultaneous effects like a two orders of magnitude decrease of hydrogen impurity content, a strong width reduction of the luminescence peaks, and an increase of crystallite sizes influencing the carrier scattering. We show that a level of structural and optical improvement as well as the final electrical parameters of annealed films strongly depend on the previously employed growth temperature, which is related to transition from oxygen- to zinc-rich conditions influencing a type and concentration of native point defects. The growth temperature does not only influence the bandgap energy but also the binding energies of existing donors and the relative ratio between the number of donors and acceptors; hence, it determines the final electrical characteristics of the films. This means that electrical properties of undoped ZnO-atomic layer deposition films can be tuned by native defects engineering.
DyVO 4 is known for its Jahn-Teller type transition [1] and interesting magnetic properties [2]. A promising application for DyVO 4 isthe catalysis in oxidative dehydrogenation of propane [3]. The DyVO 4 /V2O 5 mixture exhibits catalytic ability for decomposition of cyclohexanol [4] and strong photocatalytic activity in the decomposition of organics. A bismuth-containing solid solution, Bi 0.5 Dy 0.5 VO 4 , has been found to be useful in photoinduced water splitting [5]. DyVO 4 , like most of the RVO 4 family members, crystallizes in the zircon-type structure (I41/amd). At pressures in the range from 5 to 10 GPa, these compounds are known to undergo a phase transition into a scheelite-type polymorph (I41/a). The equation of state of a number of RVO 4 compounds has been already determined, but not for DyVO 4 . Regarding the phase transitions in DyVO 4 , in [6] the scheelite-type phase was observed at pressures above 6.5 GPa. In a recent Raman spectroscopy study [7], the zircon phase was observed up to 8 GPa, followed by a zircon-scheelite phase mixture at 8.8 and 9.2 GPa, and single-phase scheelite at 10.7 GPa and above. The aim of the present investigation is to determine the yet unknown complete set of equation-of-state parameters for both dysprosium orthovanadate polymorphs, to experimentally check, whether the transition from the zircon phase to the scheelite phase occurs in the available pressure range and to provide the theoretical coexistence pressure. To achieve this goal, X-ray diffraction experiments and density-functional-theory (DFT) calculations are applied for the first time to the study of this material at high pressures. Furthermore, the DFT calculations allowed for the determination of the variation with pressure of the internal structural parameters of the unit cells and interatomic distances. To our knowledge this information was not previously available for DyVO 4 polymorphs. The present work provides the first diffraction based experimental information on elastic properties of zircon-type and scheelite type dysprosium orthovanadates. The obtained experimental data compare well with the (first) theoretical DFT-based results. Namely, the bulk modulus equals 118 GPa (experimental) or 126 (theoretical) for the zircon phase, and equals 153 (experimental) and 142.9 (theoretical) for the scheelite phase. The good agreement supports the reliability of both, experimental and theoretical data obtained. Moreover, the quoted values are close to one of early evaluations for DyVO 4 , 126 GPa, and to those experimentally determined for some other RVO4 compounds.
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