Ab initio linear response and frozen phonons for the relaxor PMN (PbMg1/3Nb2/3O3)

Abstract

We report first principles density functional studies using plane wave basis sets and pseudopotentials and all electron linear augmented plane wave (LAPW) of the relative stability of various ferroelectric and antiferroelectric supercells of PMN for 1:2 chemical ordering along [111] and [001]. We used linear response with density functional perturbation theory (DFPT) as implemented in the code ABINIT to compute the Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies and LO-TO splittings. The polar response is different for supercells ordered along [111] and [001]. Several polar phonon modes show significant coupling with the macroscopic electric field giving giant LO-TO splittings. For [111] ordering, a polar transverse optic (TO) mode with E symmetry is found to be unstable in the ferroelectric P3m1 structure and the ground state is found to be triclinic. Multiple phonon instabilities of polar modes and their mode couplings provide the pathway for polarization rotation. The Born effective charges in PMN are highly anisotropic and this anisotropy contributes to the observed huge electromechanical coupling in PMN solid solutions.

arXiv comment34 pages, 6 figures. to appear in PRB

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• Ab initio studies of phonon softening and high pressure phase transitions of alpha-quartz SiO2
• Polar phonons and intrinsic dielectric response of the ferromagnetic insulating spinel CdCr${}_2$S${}_4$ from first principles
• First-Principles Calculation of Born Effective Charges and Spontaneous Polarization of Ferroelectric Bismuth Titanate
• Ultra-high pressure disordered eight-coordinated phase of Mg${}_2$GeO${}_4$: Analogue for super-Earth mantles
• First Principles Theories of Piezoelectric Materials
• First principles studies of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg1/3Nb2/3O3)
• Coexisting ferroelectric and antiferroelectric phases in dipole ordered substances. Material properties and possible applications