27 postulated analytically that shock loading of Cu along the 〈110〉 direction would lead to the formation of a body-centered orthorhombic (BCO) phase. The previous studies set the stage for an investigation of the possibility of phase transition in Cu at high temperature and pressure conditions. 26 provided experimental evidence that coupling between homogeneous shear and short wavelength phonon is also an essential mechanism to account for martensitic transformations of Cu-based alloys. Within the context of Landau theory, Planes et al. 24 demonstrated that low energy of the TA2 phonon vibrational mode provides the significant contribution to the excess of entropy which stabilizes BCC phase at high temperature, which has eventually been proved experimentally through a series of calorimetric and magnetic measurements 25. In fact for Cu-based shape memory alloys, Planes et al. It has been demonstrated that structural transition may be only driven by the excess of vibrational entropy of the high-temperature phase 23. Friedel 22 postulated that even though BCC phase of Cu is energetically unstable at the ground state, it may be preferred to the system at high temperature due to its large entropy resulting from low-energy vibrational transverse modes. The controversy has finally been resolved through the explanation that stable substrates influence the phase change in Cu and it can happen only in thin films and not for bulk material or even thick films 20, 21. Several researchers have demonstrated through ab − initio studies that BCC phase of Cu is energetically unstable at ground state and at ambient temperature and pressure under tetragonal deformation 18, 19 which eventually has resulted in controversy within the community of pseduomorphic epitaxy demonstrating presence of thin films of BCC Cu over different substrates. It should be noted that discovery of new phase transformation of material in bulk form is not an ordinary event and requires a mix of experimentation, predictive computations and of course luck. Phase transformation has also been reported using Neutron diffraction experiments on Cu-based shape memory alloys such as Cu-Zn-Al 14, Cu-Al-Ni 15, Cu-Al-Pd 16, Cu-Al-Be 17 in which Cu is constrained in an alloy form with other metals. Under constraint conditions such as epitaxy, thin films of BCC Cu have been grown pseudomorphically on Pd substrate 10, 11, 12, 13. There is no work in existing literature which demonstrates the existence of body-centered phase for Cu in bulk without any constraint conditions. Thereby, the discovery of an existence of body-centered phase of bulk Cu is expected to cause a revelation in the research community. In fact for many years, many experimental groups around the world use copper as the first target material in shock compression studies to develop and demonstrate new capabilities - loading conditions, diagnostics, analysis, and modeling - since Cu is believed to be a simple, well-studied material which remains FCC until melting 9. However, it is believed that Cu can only exist in face-centered-cubic (FCC) crystal structure based on which numerous phase diagrams have been prepared and used. Because of the importance and widespread usage of the material, this element has been studied extensively (both experimental 1, 2 and numerical 3, 4, 5, 6, 7, 8) along with different alloys it forms. Copper is one of the most common elements worldwide.
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