Pressure induced structural phase transition in solid oxidizer KClO$_3$: A first-principles study

High pressure behavior of potassium chlorate (KClO$_3$) has been investigated from 0-10 GPa by means of first principles density functional theory (DFT) calculations. The calculated ground state parameters, transition pressure and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO$_3$ undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4$\%$ from monoclinic (\emph{P2$_1$/m}) $\rightarrow$ rhombohedral (\emph{R3m}) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using LDA and GGA functionals, respectively. Mechanical stability of both the phases are explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 to 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO$_3$ which corroborates with the experimental results.

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