Vibrational properties and the stability of the KCuF₃phases

Abstract

We report theoretical investigations of the lattice dynamics of KCuF(3). Our calculations are based on the generalized gradient approximation and parametrization of Perdew-Burke-Ernzerhof to the density functional theory corrected for on-site Coulomb interaction (GGA + U). Vibrations of the KCuF(3) lattice are studied within the harmonic approximation. Energetic stability of tetragonal and orthorhombic polymorphic structures of KCuF(3) is analyzed. Our results show that the orthorhombic polymorph is energetically not preferred. The Raman and infrared-active phonon modes in two distinct tetragonal polymorphs of KCuF(3) are discussed with respect to the available experimental data. A detailed examination of the phonon densities of states in both tetragonal polymorphic structures of KCuF(3) is provided together with discussion on similarities and differences between the vibrational dynamics of two distinct tetragonal lattices of the KCuF(3) system.

Mechanical Properties of Tetragonal and Orthorhombic Phases of Quasi-One-Dimensional Antiferromagnet KCuF_{3}

“…Next, we determine the Debye temperature using longitudional (v l ) and transverse (v t ) sound velocities obtained from B RV H and G RV H following the Ref. [12][13][14] [3] leading to the density of 3.64 g/cm 3 , whereas the experimental value is 3.94 g/cm 3 [13]. The former value is used to evaluate the sound velocities.…”

“…For a comparison, we also derived the Debye temperature from the phonon density of states (θ Dph ), published in Ref. [3], using the procedure described in Ref. [15].…”

“…For details we refer the reader to Ref. [3] where all parameters are specied. For the calculations of elastic constants (C ij ) we applied methodology implemented in the VASP code.…”

“…[3]. It seems that the increase of the Debye temperature (θ D ) and decrease of the ductility correlates with the phase stability of the KCuF 3 polymorphs.…”

“…For the extended list of physical quantities known about the KCuF 3 as well as the description of the lattice dimensions and Wycko positions of the constituents we refer the reader to the recent publication [3]. Here, we report the single crystal elastic constants of the all three polymorphs of KCuF 3 using ab initio calculations.…”