Naslov
Cation composition dependence of superlattice reflections in (Sr/Ca/La)14Cu24O41

Autori
Milat, Ognjen

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Acta Crystallographica A66 (Supplement) ; Abstracts 26th European Crystallographic Meeting / Fuess Hartmut - Darmstadt : International Union of Crystallography, 2010, S63-s63

Skup
26th European Crystallographic Meeting, ECM 26, Darmstadt, 2010

Mjesto i datum
Darmstadt, Njemačka, 29.08.2010. - 02.09.2010

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
composite crystal; electron diffraction; charge ordering

Sažetak
Crystallographic structure of the (Sr/La/Ca)14Cu24O41 “chainladder” compounds is complex [1] due to being composed of two interpenetrated subsystems with lattice parameters mutually incommensurate along one direction. “Ladder”-subsystem is formed by the (Sr/La/Ca)2Cu2O3 layers on an orthorhombic (Fmmm) lattice, and “chain”-subsystem consists of the CuO2 interleaved layers on an (Amma) lattice [2]. While cell parameters a (≈1.14nm) and b (≈1.34nm) are common for both lattices regardless of the cation composition, the misfit between the c-parameters is found to depend on substitution and doping. The cLd/cCh ratio is always close to √2, but varies from 1.45 to 1.41 [3] for pure Sr14Cu24O41, to Sr2Ca12Cu24O41, respectively, being roughly 1.43 in La/Ca for Sr substituted La6Ca8Cu24O41. In addition, partial substitution of La for Sr affects electronic structure by reducing hole-doping on Cu2+δ. A lot of doubt has recently emerged about doped hole ordering into Wigner crystal (WC) on the 5cLd or 3cLd superlattice cells, as found by RXS [4]. This ordering is allocated onto “ladder” subsystem due to observation of weak RXS spots at reciprocal positions commensurate with “ladder”, but not with “chain” basic spots. Here, we present detailed electron diffraction study of the corresponding 4-dim reciprocal lattice, and prove that all spots can be indexed: H = ha* + kb* + lcLd* + mcCh*. Spot`s intensity depends more on local imaging conditions and degree of order, then on nominal composition. By varying the Sr/La/Ca composition and the corresponding cLd/cCh ratio, all reciprocal lattice points shift in positions along c* ; the range (1/5cLd*- 1/3cLd*), coinciding to (1/7.1cCh*- 1/4.3cCh*), is swept by the weak spot 0046. Therefore, the peaks observed in that range should be assigned as 0046 reflection, and could not be exclusively related to “hole" superlattice formation in “ladder” subsystem only, as claimed for 5cLd WC in Sr14Cu24O41 [4]

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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