Experimental and DFT study on the physical properties of p-type semiconductors oxides for thermoelectric applications.

Abstract

In the present work, pure and alkali doped NiO (Ni1-xAxO) and La-alkali co-doped (Ni1-2yAyLayO) NiO thin films where (A=Li, Na and K) and (x=0.03, 0.06, 0.09, 0.125 and 0.25) and (y=0.03, 0.06) were synthesized by sol-gel spin coating method and deposited on glass substrates. XRD analysis showed that the prepared films belongs to a cubic structure with (100) plane wave as preferential growth orientation for pure and K doped NiO for small K contents and the (200) for higher K contents along with Li, Na, and La-alkali co-doped NiO thin films. The grain size decreased with the increase of the concentration of doping elements in the NiO lattice. Optical properties of the prepared films were investigated. As x increased the transparency of the prepared films decreased. Also the optical study revealed that the optical band gap tends to decrease with alkali doping and achieves minimal values with Na doping. The Urbach energy increases systematically with the decrease of the optical band gap. The resistivity measurements showed that the alkali doping and La-alkali co-doping led to a significant decrease in the resistivity values. Structural, electronic, optical and elastic properties of pure and alkali doped NiO (Ni1-xAxO) and La-alkali co-doped (Ni1-2yAyLayO) NiO thin films where (A=Li, Na and K) and (x=0.03, 0.06, 0.125 and 0.25) and (y=0.03, 0.06) were performed using the first principle method based on density functional theory. The optimization of the geometry of the studied samples revealed that lattice parameter is affected with alkali doping and La-alkali co-doping. The band structure and density of states calculations showed that doped and co-doped samples exhibited an indirect band gaps. The optical parameters: ε1(ω),ε2(ω),n(ω),k(ω),α(ω),R(ω) ,L(ω)and elastic constants: (𝐶𝑖𝑗,𝐵,𝐺,𝐸,𝜈 𝑎𝑛𝑑 𝐵𝐺⁄), the longitudinal and shear wave velocities (𝑉𝑙,𝑉𝑠), and Debye temperature 𝜃𝐷 were father investigated.Both experimental and theoretical results obtained in this work are in good agreement.