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Karuna Mishra1 Thoguluva Ravindran2 Krishan Pandey3 Ram Katiyar1

1, University of Puerto Rico at Rio Piedras, San Juan, Puerto Rico, United States
2, Indira Gandhi Centre for Atomic Research , Kalpakkam, Tamil Nadu, India
3, Bhabha Atomic Research Centre, Mumbai, Maharastra, India

Two-dimensional layered trichalcogenides are of current research interest because of their robust opto-electronics, and thermal properties. Mechanical and phonon vibrational properties of these materials are of significant importance in the field of stress and thermal management. Here we report the pressure dependence of structural and phonon behaviors of high quality few-layers vanadium diselenide nano-sheets, grown by hydrothermal method, employing synchrotron x-rays and micro-Raman scattering techniques. The high crystalline nature of the nanosheets was examined using transmission electron microscopy. Synchrotron x-ray studies at high pressure (up to 22 GPa) using a diamond-anvil cell identify a displacive type phase transition to a low symmetry monoclinic phase (C2/m) around 7 GPa corroborated with the P-dependent Raman scattering results. Raman spectroscopic studies at high pressure (up to 34 GPa) identify two prominent Raman bands with symmetry Eg and A1g. Upon increasing pressure Eg band at 207 cm-1 shows normal hardening and A1g band at 236 cm-1softens. The first order pressure derivatives of these phonons at ambient phase (P-3m1) are found to be -3.547(2) and 0.388(6) cm-1/ GPa, respectively. Using the experimental mode Grüneisen parameter of Eg Raman mode, the in-plane thermal expansion coefficient of the titular compound at the ambient phase is estimated. The observed results are expected to be useful in calibration and performance of next generation nano-electronics and optical devices under extreme stress conditions. These experimental results corroborated with our ab-initio calculations will be presented later.

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