Growth of Ca2MnO4 Ruddlesden-Popper structured thin films using combinatorial substrate epitaxy

M Lacotte,C Grygiel,R De Kloe,M Velazquez,A David,G S Rohrer,D Pravarthana,W Prellier,P A Salvador

doi:10.1063/1.4905012

Abstract

The local epitaxial growth of pulsed laser deposited Ca2MnO4 films on polycrystalline spark plasma sintered Sr2TiO4 substrates was investigated to determine phase formation and preferred epitaxial orientation relationships (ORs) for isostructural Ruddlesden-Popper (RP) heteroepitaxy, further developing the high-throughput synthetic approach called Combinatorial Substrate Epitaxy (CSE). Both grazing incidence X-ray diffraction and electron backscatter diffraction patterns of the film and substrate were indexable as single-phase RP-structured compounds. The optimal growth temperature (between 650 °C and 800 °C) was found to be 750 °C using the maximum value of the average image quality of the backscattered diffraction patterns. Films grew in a grain-over-grain pattern such that each Ca2MnO4 grain had a single OR with the Sr2TiO4 grain on which it grew. Three primary ORs described 47 out of 49 grain pairs that covered nearly all of RP orientation space. The first OR, found for 20 of the 49, was the expected RP unit-cell over RP unit-cell OR, expressed as [100][001]film||[100][001]sub. The other two ORs were essentially rotated from the first by 90°, with one (observed for 17 of 49 pairs) being rotated about the [100] and the other (observed for 10 of 49 pairs) being rotated about the [110] (and not exactly by 90°). These results indicate that only a small number of ORs are needed to describe isostructural RP heteroepitaxy and further demonstrate the potential of CSE in the design and growth of a wide range of complex functional oxides.

Highlights

The Ruddlesden-Popper (RP) type phases are perovskitelike layered oxides of the general formula Anþ1MnO3nþ1 (or AO(AMO3)n),1–3 where A is typically a rare earth or alkaline earth ion and M is a transition or post-transition metal ion
The other two orientation relationships (ORs) were essentially rotated from the first by 90, with one being rotated about the [100] and the other being rotated about the [110]. These results indicate that only a small number of ORs are needed to describe isostructural RP heteroepitaxy and further demonstrate the potential of Combinatorial Substrate Epitaxy (CSE) in the design and growth of a wide range of complex functional oxides
We have previously demonstrated with CSE, using typical growth conditions to obtain epitaxial films on single crystals, that: (1) grain-over-grain epitaxy occurs for most orientations of substrate grains, (2) only a small number of orientation relationships, ORs, exist for simple structures, (3) similar results are obtained for the growth of heterostructured complex oxide films using CSE as are obtained for films grown on single crystals, and (4) metastable and new complex oxides can be stabilized using CSE

Summary

Introduction

The Ruddlesden-Popper (RP) type phases are perovskitelike layered oxides of the general formula Anþ1MnO3nþ (or AO(AMO3)n), where A is typically a rare earth or alkaline earth ion and M is a transition or post-transition metal ion. The perovskite-like end-members of this family are the n 1⁄4 1 AMO3 perovskites and the n 1⁄4 1 A2MO4 RP phases (a structure known the K2NiF4 structure). The structure of the RP family is described by the stacking of n consecutive perovskite layers, AMO3, alternating with a single AO rock-salt layer along the crystallographic c-direction. The reduced dimensionality of the M-O bonding plays an important role in the properties of RP phases, but the large unit cells and anisotropic nature of the RP crystal structures make synthesis of high-quality crystals, powders, and films more challenging than that of the related perovskites. RP phases played important roles in the discovery of hightemperature superconductivity, and the manganese-based

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