Off-Stoichiometry Effects on the Crystalline and Defect Structure of Hexagonal Manganite REMnO₃ Films (RE = Y, Er, Dy)

Abstract

The crystalline and defect structure of epitaxial hexagonal RE x Mn y O3 (RE = Er, Dy) films with varying cationic composition was investigated by X-ray diffraction and transmission electron microscopy. The films are composed of a strained layer at the interface with the substrate and of a relaxed layer on top of it. The critical thickness is of ∼10 to 25 nm. For Mn-rich films (or RE deficient), an off-stoichiometric composition maintaining the hexagonal LuMnO3-type structure is stabilized over a large range of the RE/Mn ratio (0.72−1.00), with no Mn-rich secondary phases observed. A linear dependence of the out-of-plane lattice parameter with RE/Mn is observed in this range. Out-of-phase boundary (OPB) extended defects are observed in all films and exhibit a local change in stoichiometry. Such a large solubility limit in the RE deficient region points toward the formation of vacancies on the RE site (RE x MnO3−δ, with 0.72 ≤ x < 1), a phenomenon that is encountered in perovskite manganites such as La x MnO3−δ (x < 1) and that may strongly impact the physical properties of hexagonal manganites.

Defect Chemistry as a Crystal Structure Design Parameter: Intrinsic Point Defects and Ga Substitution in InMnO3

“…We anticipate strong effects, since RMnO 3 have already been shown to tolerate significant oxygen deficiency down to 3 − δ = 2.75, 28 excess oxygen up to δ = 0.35 29,30 and R 3+ deficiency down to 1 − x = 0.72. 31 The possibility of In deficiency is even more likely due to the relatively high volatility of In at typical temperatures for single-crystal growth or sintering of polycrystals, with a vapor pressure over solid In at 950°C for example of 5.4 × 10 −5 atm. 32 In this work we use first-principles electronic structure calculations based on density functional theory to perform a comprehensive study of the role of various defects in determining the ground state polar or non-polar structure of InMnO 3 , as well as the resulting properties.…”

Crystal structure, magnetic and dielectric behavior of h-LuMn O3± ceramics (0.95≤x≤1.04)

“…In the effort to explain and ascertain the interdependence of each ferroic property on the observed physical and chemical properties of these materials, authors have mainly dealt with Asite or B-site doping approaches [2,[5][6][7][8] or by changing synthesis conditions [9][10][11][12][13]. Although, upon doping or changing synthesis conditions, one is able to change the ferroic properties, still from all these experimental adjustments and theoretical approaches the role of rare-earth and metal ions on unit cell parameters and magnetic and dielectric properties could not be clearly and explicitly figured out.…”

“…Only lattice modification of the h-RMnO 3 (R= Y, Er and Dy) off-stoichiometric thin films were studied [12]. Stabilized by the substrate constraining, the linear increase of the outof-plane c-axis from ErMn 1.39 O 3±δ to ErMn 0.80 O 3±δ composition of the thin films indicates a stability domain of the solid solution much wider than stability limits of the same hexagonal phase in polycrystalline ceramics of ErMn x O 3±δ at 1200-1400 ºC as determined by the criterion of absence of secondary phases in inspection of powder XRD results [12,24].…”

Breaking the geometric magnetic frustration in controlled off-stoichiometric LuMn1+zO3+δ compounds

“…The two main mechanisms to preserve charge neutrality of a doped system (z) are considered: partial oxidation of Mn ions and/or formation of oxygen vacancies [27]. In particular, charge compensation mechanisms due to each Mn deficit lead up to 3 valence electrons default which, for δ ~0, in the pseudo-perovskite systems can impinge [28].…”