Nonstoichiometry in the La,_,Sr,NiO,+, system

M.J. SAYAGUEZ; M. VALLET-REGI; A. CANEIRO; J.M. GONZALEZ CALBET

SOLID STATE IONICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1993 vol. 66 p. 21 - 26

0167-2738

An electron diffraction study of the La,_$r,NiO 4+d system ( - 0.07 5610.14) shows that compositional variations can beaccommodated in two different ways as a function of 6. For 6z= 0.06, interstitial oxygens are ordered leading to new K,NiF,superstructural types. When 8~0, nonstoichiometry is either acccommodated by means of random distribution of anionic vacanciesor by means of disordered intergrowths of both K2NiF4 and Sr,CuO,-type structures.1. IntroductionThe striking structural similarities betweenLa2_.,.(Ba, Sr),CuO_,+d [ 1 ] and La2_,SrXNi04+amaterials have stimulated the research on the lattersystem [2,3] as an alternative route to understandthe mechanisms controlling the superconductivity incopper oxides. Both La&uO, and La2Ni04 [ 21 areisostructurals, being able to incorporate oxygen excessinto the K2NiF4 structural-type. In fact, bothsystems show a wide range of oxygen nonstoichiometry[ 41, since this structural type can either incorporateinterstitial oxygens or introduce anionicvacancies. Since both structure and physical propertiesare dependent upon the stoichiometry, an accuratecontrol of the oxygen content is necessary.Several neutron diffraction studies [5,6] performedon La2Ni0,+d show a two-phase field for0.02 I SI 0.14, very close to the behavior describedfor La2Cu04+6 [ 71, the interstitial oxygen defectbeing located near the ( l/4, l/4, l/4) sites in theorthorhombic structure.* Paper presented at the 12th ISRS Conference, Madrid, September24-30, 1992; received by Publisher 1 June 1993.’ Permanent address: Centro Atdmico Bariloche, 8400 SC Bariloche,Argentina.’ To