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      Evolution of the Structural, Mechanical, and Phonon Properties of GeSe Polymorphs in a Pressure-Induced Second-Order Phase Transition

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          Abstract

          A pressure-induced structural transition from the layered-like phase ( Pnma) to another bilayer structure ( Cmcm) in GeSe was investigated with first principle calculations. The variations of the structural, electronic, elastic, and vibrational properties of GeSe with the application of pressure were obtained. The transformation from the Pnma to Cmcm phase occurred at 34 GPa. The Cmcm phase structure showed dynamical stability above 37 GPa. The lattice parameters and the equation of state varied continuously at the transition pressure. Obvious stiffening in the C 33 and C 23 elastic constants associated with the compressive and shear components was observed to occur within the phase transition process. Two characteristic Raman modes (A g and B 3g) of the Pnma phase showed significant softening by increasing the pressure.

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          A simple measure of electron localization in atomic and molecular systems

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            Symmetry-general least-squares extraction of elastic data for strained materials fromab initiocalculations of stress

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              Single-crystal colloidal nanosheets of GeS and GeSe.

              Narrow-band-gap IV-VI semiconductors offer promising optoelectronic properties for integration as light-absorbing components in field-effect transistors, photodetectors, and photovoltaic devices. Importantly, colloidal nanostructures of these materials have the potential to substantially decrease the fabrication cost of solar cells because of their ability to be solution-processed. While colloidal nanomaterials formed from IV-VI lead chalcogenides such as PbS and PbSe have been extensively investigated, those of the layered semiconductors SnS, SnSe, GeS, and GeSe have only recently been considered. In particular, there have been very few studies of the germanium chalcogenides, which have band-gap energies that overlap well with the solar spectrum. Here we report the first synthesis of colloidal GeS and GeSe nanostructures obtained by heating GeI(4), hexamethyldisilazane, oleylamine, oleic acid, and dodecanethiol or trioctylphosphine selenide to 320 °C for 24 h. These materials, which were characterized by TEM, SAED, SEM, AFM, XRD, diffuse reflectance spectroscopy, and I-V conductivity measurements, preferentially adopt a two-dimensional single-crystal nanosheet morphology that produces fully [100]-oriented films upon drop-casting. Optical measurements indicated indirect band gaps of 1.58 and 1.14 eV for GeS and GeSe, respectively, and electrical measurements showed that drop-cast films of GeSe exhibit p-type conductivity.
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                Author and article information

                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                03 November 2019
                November 2019
                : 12
                : 21
                : 3612
                Affiliations
                [1 ]School of Physics and Electronic Engineering, Leshan Normal University, Leshan 614004, China; yjh20021220@ 123456foxmail.com
                [2 ]State Key Laboratory of Electrical Insulation and Power Equipment & School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China; bingxiao84@ 123456xjtu.edu.cn
                [3 ]College of Optoelectronic Technology, Chengdu University of Information Technology, Chengdu 610225, China; dyccqzx@ 123456cuit.edu.cn
                Author notes
                [* ]Correspondence: fanq@ 123456lsnu.edu.cn
                [†]

                Authors have contributed equally to this work.

                Author information
                https://orcid.org/0000-0002-3059-2436
                Article
                materials-12-03612
                10.3390/ma12213612
                6862562
                31684184
                07226130-8384-4bb4-bab0-1e3a64672105
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 03 September 2019
                : 31 October 2019
                Categories
                Article

                phase transition,first principle calculations,elastic constant,phonon mode softening

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