Evidence of In-Plane Superstructure Formation in Phase-Separated and Staged Single CrystalLa2CuO4+δ

Abstract

In single crystal La 2 CuO 41d , d ϳ 0.015, c-axis interstitial oxygen ordering (staging) in the oxygenrich phase of the phase-separated sample was observed through satellite peaks in the neutron scattering at ͑0, 1, 4 6 ϳ0.16͒ which first appear at 250 K. A superconducting T c Ӎ 31 K was achieved by prolonged annealing at 200 K of a staged crystal whose T c was subsequently enhanced by ϳ1.5 K during a 7 h cooling from 215 to 190 K. This annealing below 215 K initiates a splitting of the staging satellites along the a ‫ء‬ direction which signifies a one-dimensional modulation of the in-plane order. PACS numbers: 74.72.Dn, 74.62.Bf Oxygen-intercalated La 2 CuO 41d is among the simplest of the family of the new superconducting Cu oxides with a superconducting T c as high as 34 K for 0.01 # d # 0.05; its structure and phase diagram have therefore attracted considerable attention [1]. Composition, pressure, and thermal history-dependent superconductivity have been observed in this material [2,5], which indicates that subtle structure modifications cause substantial changes in the superconducting properties. Although considerable progress has been made in understanding these effects, the detailed structures have, until recently, not been well determined, although phase separation into oxygen-rich and oxygen-poor regions has been observed [6-9]. Wells et al. [9] have, in addition, shown in single crystal neutron scattering studies of La 2 CuO 41d that the oxygen-rich phases undergo, on cooling, a layering of the intercalated oxygen with attendant phase shifts of the octahedral tilts in the intervening layers as also occurs in the welldocumented La 2 NiO 41d studies of Tranquada et al. [10]. The layering is reminiscent of the staging seen in graphite intercalation compounds and may well require similar consideration of Daumas-Herold domain formation [11] in which each plane has an equal intercalant concentration which is staged. As a local probe, NMR measurements provide evidence for localized holes in the CuO 2 planes of O-doped lanthanum cuprate, and it has been shown that the anomalous copper site in the CuO 2 plane neighbors the interstitial oxygens [12]. The diffusion of single hole clusters which are space limited at 150 # T # 170 K and space unrestricted above 180 K has also been suggested in La 2 CuO 41d [13].Adiabatic calorimetry [5] has revealed three structural phase transitions in a La 2 CuO 4.011 single crystal at 287, 265, and 222 K, respectively, with different superconductivity transition temperatures for the two low temperature phases and it shall partly be our purpose here to identify structurally these transitions.In this Letter, we report novel neutron diffraction and preliminary magnetic susceptibility results on a high quality single crystal of La 2 CuO 41d with d ϳ 0.015. We supply evidence for a reversible temperature-induced in-plane superstructure formation which modulates the layered-intercalated O-rich phase into which our crystal has already phase separated (as in [9]). The single crystal...

Thermally activated dynamics of the tilts of the CuO6octahedra, hopping of interstitial O, and possible instability towards the LTT phase in La2CuOCordero1, Grandini2, Cannelli3 et al. 1998Phys. Rev. B365240View full textAdd to dashboardCite

“…Such pairs could also be identified with the interstitial O atoms with partially covalent bond, which have been invoked to explain a doping efficiency of less than two holes per excess O atom. 24,38 In the doped samples we did not observe any clear sign of phase separation into O-rich and O-poor phases, nor of 26,27 within the O-rich phase, but it is possible that these transitions occurred and were masked by the intense relaxations O1 and O2.…”

“…24 In fact, the interstitial O atoms are mobile down to 150 K ͑Refs. 4,25͒ and separate into O-rich and O-poor phases; superstructures have also been observed in the O-rich phase due to the segregation of the interstitial atoms in occupied layers spaced by n empty layers ͑staging͒, 26,27 and the relationship between the oxygen phase separation and the hole phase separation has to be clarified. 28 It appears that the modulations of the octahedral tilts, the ordering and aggregation of interstitial O, the electronic and magnetic phase separations and the superconducting properties are all interconnected to each other.…”

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

“…A similar phenomenon has been thoroughly studied in graphite intercalation compounds (GIC's) [647], where it is known as staging. Staging was initially reported for a related compound, La 2 NiO 4+δ (LNO), when doped by excess oxygen [648], but has more recently been found in the cuprates [649,650]. Intercalation is a phenomenon in which the dopant atoms or molecules form intercalated layers, with a fairly uniform composition, between the layers of the host molecule (graphite, LNO).…”

Systematic study of short-range antiferromagnetic order and the spin-glass state in lightly dopedLa2−xSrx

“…Note that another doping case by an insertion of excess oxygens is supposed to be an annealed system, where the doped oxygens are staged and also ordered in each staged layer at slow cooling stage. 18,19 In the quenched spin-glass system, magnetic susceptibility is postulated to result from the sum of a temperature independent residual susceptibility and a Curie type magnetic susceptibility:…”

“…In addition, data for x = 0 was determined from a single crystal of La 2 CuO 4 that was grown by the method reported in Ref. 19 and annealed in Ar atmosphere at 900 • C for 12 hours. As clearly shown in Fig.1, the c-axis lattice constants of the lower doped samples extrapolate smoothly from the published data.…”