摘要
Double perovskite oxides,with generalized formula A_(2)BB'O_(6),attract wide interest due to their multiferroic and charge transfer properties.They offer a wide range of potential applications such as spintronics and electrically tunable devices.However,great practical limitations are encountered,since a spontaneous order of the B-site cations is notoriously hard to achieve.In this joint experimental-theoretical work,we focused on the characterization of double perovskites La2TiFeO6 and La_(2)VCuO_(6) films grown by pulsed laser deposition and interpretation of the observed B-site disorder and partial charge transfer between the B-site ions.A random structure sampling method was used to show that several phases compete due to their corresponding configurational entropy.In order to capture a representative picture of the most relevant competing microstates in realistic experimental conditions,this search included the potential formation of non-stoichiometric phases as well,which could also be directly related to the observed partial charge transfer.We optimized the information encapsulated in the potential energy landscape,captured via structure sampling,by evaluating both enthalpic and entropic terms.These terms were employed as a metric for the competition of different phases.This approach,applied herein specifically to La_(2)TiFeO_(6),highlights the presence of highly entropic phases above the ground state which can explain the disorder observed frequently in the broader class of double perovskite oxides.
基金
Part of this work was performed at the Stanford Nano Shared Facilities(SNSF)
supported by the National Science Foundation under award ECCS-1542152
C.W.was supported by a grant[EP/R02992X/1]from the UK Engineering and Physical Sciences Research Council(EPSRC)
This work was performed using resources provided by the ARCHER UK National Supercomputing Service and the Cambridge Service for Data-Driven Discovery(CSD3)operated by the University of Cambridge Research Computing Service(www.csd3.cam.ac.uk),provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council(capital grant[EP/P020259/1])
DiRAC funding from the Science and Technology Facilities Council(www.dirac.ac.uk).C.W.and D.B.are grateful to Antoine George,Nicola Bonini,and Francesco Macheda for insightful discussions.C.J.P.acknowledges the support of a Royal Society Wolfson Research Merit award.E.F.and D.B.thank Matteo Coccioni and Iurii Timrov for useful insights.
