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End date: 2024 × Start date: 2020 × End date: 2021 × Start date: 2020 × DDC: 500 × Type: article × WGL Institute: IOM ×

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    Conversion of p–n conduction type by spinodal decomposition in Zn-Sb-Bi phase-change alloys
    ([London] : Macmillan Publishers Limited, part of Springer Nature Tokyo, 2020) Wang, Guoxiang; Shi, Haizhou; Lotnyk, Andriy; Shi, Daotian; Wang, Rongping
    Phase-change films with multiple resistance levels are promising for increasing the storage density in phase-change memory technology. Diffusion-dominated Zn2Sb3 films undergo transitions across three states, from high through intermediate to low resistance, upon annealing. The properties of the Zn2Sb3 material can be further optimized by doping with Bi. Based on scanning transmission electron microscopy combined with electrical transport measurements, at a particular Bi concentration, the conduction of Zn-Sb-Bi compounds changes from p- to n-type, originating from spinodal decomposition. Simultaneously, the change in the temperature coefficient of resistivity shows a metal-to-insulator transition. Further analysis of microstructure characteristics reveals that the distribution of the Bi-Sb phase may be the origin of the driving force for the p–n conduction and metal-to-insulator transitions and therefore may provide us with another way to improve multilevel data storage. Moreover, the Bi doping promotes the thermoelectric properties of the studied alloys, leading to higher values of the power factor compared to known reported structures. The present study sheds valuable light on the spinodal decomposition process caused by Bi doping, which can also occur in a wide variety of chalcogenide-based phase-change materials. In addition, the study provides a new strategy for realizing novel p–n heterostructures for multilevel data storage and thermoelectric applications.
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    Strongly enhanced and tunable photovoltaic effect in ferroelectric-paraelectric superlattices
    (Washington, DC [u.a.] : Assoc., 2021) Yun, Yeseul; Mühlenbein, Lutz; Knoche, David S.; Lotnyk, Andriy; Bhatnagar, Akash
    Ever since the first observation of a photovoltaic effect in ferroelectric BaTiO3, studies have been devoted to analyze this effect, but only a few attempted to engineer an enhancement. In conjunction, the steep progress in thin-film fabrication has opened up a plethora of previously unexplored avenues to tune and enhance material properties via growth in the form of superlattices. In this work, we present a strategy wherein sandwiching a ferroelectric BaTiO3 in between paraelectric SrTiO3 and CaTiO3 in a superlattice form results in a strong and tunable enhancement in photocurrent. Comparison with BaTiO3 of similar thickness shows the photocurrent in the superlattice is 103 times higher, despite a nearly two-thirds reduction in the volume of BaTiO3. The enhancement can be tuned by the periodicity of the superlattice, and persists under 1.5 AM irradiation. Systematic investigations highlight the critical role of large dielectric permittivity and lowered bandgap.