Abstract:
Lutetium iron oxide (LFO) is a type-II multiferroic material which exhibits
ferroelectric and magnetic orders, making them interesting for various technological
applications include spintronic, memory devices, sensors, and phase shifters. Shifting
electric ordering makes LFO a promising material for phase shifting applications due
to its unique ferroelectric behavior responsible for change in electronic properties i.e.
dielectric constant. Doping strategy is one way to optimize the dielectric constant for
specific phase shifting application. The primary aim of this research is to explore the
structural and dielectric characteristics of La-doped h-LFO using DFT in CASTEP
software. LFO, P63cm phase is investigated using first-principles calculations based
on the GGA-PBE approximation with Hubbard U (GGA-PBE+ U) method in the
frame of plane-wave pseudo-potential density functional theory (DFT). The indirect
band gap of 0.54 eV is calculated from the band structure which converted into direct
band gap with value 0.514 eV after doping lanthanum atom at A-site in LFO
supercell. The reduction in band gap is due to increase in partial and total density of
sates which have great influence on the electric and optical properties. Partial density
of states shows increase in total density of states. Lanthanum contributes p-state in the
valence band and small contribution from d-state in the conduction band. Substitution
of La-atom at the A-site of LFO significantly decreases the dielectric constant from
19.2 to 18.7. A minimal change in electronic disorder is observed due to small
difference in the oxidation states of the Lu3+ and La3+as the structure disorder
associated with ionic size difference between dopant and substituted atom. The
change in the refractive index is also observed from 4.38 to 4.32 and also reflectivity
decreases from 0.634 to 0.627.
