  Although rare earth nickelates (ReNiO3) exhibit abundant electronic phases
and widely adjustable metal to insulator electronic transition properties,
their practical electronic applications are largely impeded by their intrinsic
meta stability. Apart from elevating oxygen reaction pressures, heterogeneous
nucleation is expected as an alternative strategy that enables the
crystallization of ReNiO3 at low meta stability. In this work, the respective
roles of high oxygen pressure and heterogeneous interface in triggering ReNiO3
thin films growth at metastable state are revealed. The ReNiO3 (Re:Nd, Sm, Eu,
Gd, and Dy) heterogeneous thin films growth on LaAlO3 single crystal substrate
have an effective crystallization at atmosphere without the necessity to apply
high oxygen pressures, suggesting the interfacial bonding between the ReNiO3
and substrates can sufficiently reduce the positive Gibbs formation energy of
ReNiO3, which is further verified by the first principles calculations.
Nevertheless, the abrupt electronic transitions only appear in ReNiO3 thin
films grown at high oxygen pressures, in which cases the oxygen vacancies are
effectively eliminated via high oxygen pressure reactions as indicated by near
edge X ray absorption fine structure (NEXAFS). This work unveils the
synergistic effects of heterogeneous nucleation and high oxygen pressure on the
growth of high quality ReNiO3 thin films.
