Raman Band Redshifting of α-Cu2(OH)3Cl with Decreasing the Temperature

摘要

Raman spectra of the magnetic geometric frustration material-the botallackite-structure α-Cu2(OH)3C1 polycrystalline sample were measured down to liquid N2 temperature.It is found that the hydroxyl stretching bands shift abnormally according to the lattice thermal expansion effect of normal materials,i.e.,they redshift with decreasing the sample temperature (negative thermal expansion) using liquid N2 cooling while other bands blueshifl.This abnormality was also confirmed by observing the band-shifting caused by local laser heating effect using different laser powers,and can be qualitatively explained by checking the local hydroxyl environment with a trimeric hydrogen bond.