Pressure Induced Phase Transformation Of Botallackite Cu2?OH?₃Cl With A Two Dimensional Layered Structure Synthesized Via A Hydrothermal Strategy

Botallackite??-Cu₂?OH?₃Cl?exhibits exotic unconventional magnetic transitions and magnetic ordering structures and thus attracts considerable research enthusiasm.It has a two-dimensional layered structure,and adjacent thin layers are connected by its unique interlayer trimeric hydrogen bond??OH?₃···Cl?.In terms of composition and structure,Botallackite??-Cu₂?OH?₃Cl?can be considered as a member of the layered metal hydroxyl halide/oxide family.In addition to the relationship between structure and properties,the study of hydroxyl copper chloride also provides a prerequisite for the study of a series of derivatives of hydroxyl copper chloride.In this work,free-standing?-Cu₂?OH?₃Cl nanoflakes with high purity and crystallinity are synthesized via a template-free hydrothermal strategy.Powder X-ray diffraction studies confirm that?-Cu₂?OH?₃Cl crystallizes in a brucite-like monoclinic lattice characteristic of a hydrogen bonded two-dimensional layered structure.The quantitative elemental analysis by using EDX spectra indicates the perfect stoichiometry of the prepared sample.The morphological features observed via SEM and TEM techniques reveal that the prepared sample is composed of single crystalline nanosheets with the thickness ranging from 20 to 30 nm.The vibrational modes and their frequencies observed in FTIR absorption and Raman scattering measurements may be assigned to the bonding nature of?-Cu₂?OH?₃Cl.The band gap of the obtained?-Cu₂?OH?₃Cl nanoflakes is estimated to be 2.82 eV through UV-vis absorption spectra recorded at ambient conditions.The compression behavior of?-Cu₂?OH?₃Cl nanoflakes is investigated by in situ high pressure synchrotron radiation angle dispersive X-ray diffraction up to 48.4GPa.A first-order reversible structural phase transformation is observed to begin at 13.8 GPa and complete at 24.4 GPa,with coexistence of the two phases in the intermediate pressure range.A disordered rutile-type CdOHF-related structure is postulated for the novel high pressure phase,which persists to the highest pressure in this study.After a series of analyses,the structure of the high-pressure phase was refined with GSAS software,and the results showed that the high-pressure phase was a CdOHF-like rutile structure.The lattice parameters of each pressure point are calculated and the change of lattice parameters with pressure is given.The pressure dependences of the unit cell volumes of the two phases are fitted to the third-order Birch-Murnaghan equation of state,to acquire more information about the mechanical properties of Cu₂?OH?₃Cl.The information of elastic modulus and its pressure derivative before and after the phase change is obtained from the equation of state.The high pressure Raman scattering spectrum has been tested,and the reason why the Raman scattering signal gradually disappears is explained.The Raman peak signal of each frequency is referred to the corresponding Raman mode,and the Gruneisen coefficient of each Raman mode has been calculated.Finally,the high pressure uv-visible absorption spectrum of the sample was tested,and it was found that the absorption edge was significantly red-shifted around 13 GPa,which was exactly corresponding to the structural phase transition in the high pressure synchrotron radiation experiment.The pressure-relief experiment proved that the change in the high pressure ultraviolet was also reversible.The variation of the electronic energy band gap with pressure is measured by using the in situ high pressure UV-vis absorption spectra.A sharp decrease of Eg in the pressure range of11.1-13.0 GPa confirms the onset of the structural phase transformation.The study of the structure,properties,compression behavior and phase change mechanism of?-Cu₂?OH?₃Cl in this paper provides insight into the structural topological evolution of two-dimensional layered material family with hydrogen bonds,and is of great significance for the study of the structural characteristics of hydroxyl copper chloride derivatives and the pressure response of low-dimensional layered nanomaterials.