Perovskite-type
KMgF3, which represents a distinct class
of multifunctional materials, has drawn immense interest in the advanced
technological fields due to its various attractive properties. However,
these properties are strongly influenced by the presence of various
vacancy point defects in the host crystal structure. This drives us
to gain a detailed knowledge of the defect chemistry in KMgF3 by investigating geometry, electronic structure, defect formation
energies, and charge transition levels. To achieve reliable results,
we have adopted hybrid density functional calculations. To find out
the stable growth condition for all possible vacancy defects and vacancy
cluster defects in KMgF3, calculations of defect formation
energies under different chemical potential range have been carried
out. Among all the vacancy defects considered in this study, the calculated
formation energy for VMg in a −2 charge state is
found to be a more negative value as the Fermi energy level approached
toward the conduction band minimum irrespective of the chemical potential
range. The present study explored the role of different vacancy defects
in creating impurity states in the band gap region by detailed analysis
of electronic structure in each case. It has been observed that the
impact of anion vacancy and their aggregation on the electronic structure
of KMgF3 is much more prominent than that of cation vacancy.
The electrical and optical properties of KMgF3 in the presence
of various defects have been described on the basis of calculated
thermodynamic and optical charge transition levels, respectively.
It has been revealed that the cation vacancy defects are not likely
to form deep defect states, while anion vacancy and their aggregation
act as deep donor defects. The mixed cluster vacancy of K and F pair
behaves differently with respect to Mg and F pair in the optical property.
The cation vacancies have hardly any contribution to the observed
optical spectrum, which is consistent with experimental observation.
Thus, an unambiguous and ultimate clarification of the fundamental
absorption and emission processes in KMgF3 has been accomplished
in the present study.