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1. INTRODUCTION an inward relaxation of topmost layers was found. However within the terminating layer the atoms behave differently. In LaO layer - O atoms relax outwards and La atoms opposite. While for NiO2 slab the O atoms relax inwards and Ni atoms opposite. The calculated Mulliken charge transfer indicates that there is a change of bondlengths. For La the charge is reduced from 1.58e down to 1.30e with a probable elongation of La-O bond and weakened interaction. In NiO2 terminated surface the Ni charge increases from 0.48e to 0.65 e which could indicate an increase contribution of Ni3d electrons to electronic transport at the surface. It is reflected in calculations by increased density of states (DOS) at the Fermi level in comparison to LaO terminated surface. Calculations of surface energy and DOS of unrelaxed, atomically relaxed and fully relaxed surfaces were done(44). It was found that within the full-relaxed sur- faces LaO3 and all Ni containing terminations like NiO2, LaNiO, Ni, have higher surface energy than LaO termination which was 0.7 eV. The authors assumed nominal charges for the ions to discuss the polarity influence on surface stability. With these assumptions the LaO and NiO2 terminated surfaces have a polari- ties of +1 and -1, respectively. An attempt to investigate the polarity effect was made. The authors claim that a surface constructed by removing 50 % of the atoms should be non-polar. For such surfaces the DOS indeed different shape, which authors contribution to polarity suppression and contribution of uncovered stated of a sublayer. 1.4.1 Crystallographic structure of SmNiO3 thin films Growth conditions play a huge role in ’inducing’ crystal structure guaranteeing phase stability of thin films. Approximate analysis of thermodynamic trends was carried out based on Gibbs free energy of formation of SNO (61) ∆G = ∆HLNO,1000K − T∆SLNO,1000K + h(r(R3+)) − r(R3+) − (1/4)RTln(P). (1.18) LNO stands for LaNiO3, R is the ideal gas constant, and the last term accounts for variable oxygen pressure P. The obtained calculated diagram indicates that the stability of films is best if they undergo extreme annealing at high temperature and pressure. However for typical (p < 800 μbar T > 800K) perovskite thin films growth conditions are insufficient to bring a phase stability. For radio-frequency (RF) magnetron sputtered films as-grown (13 mbar (10 mTorr) total pressure, 80/20 sccm Ar/O2 gas flow, 200 W, and 470 K) or annealed at 620 K in 100 bar O2 - there were no peaks of film in diffraction patterns, only 24PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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