Hexagonal Perovskites as Quantum Materials

Abstract

Hexagonal oxide perovskites, in contrast to the more familiar perovskites, allow for face-sharing of metal-oxygen octahedra or trigonal prisms within their structural frameworks. This results in dimers, trimers, tetramers, or longer fragments of chains of face-sharing octahedra in the crystal structures, and consequently in much shorter metal-metal distances and lower metal-oxygen-metal bond angles than are seen in the more familiar perovskites. The presence of the face-sharing octahedra can have a dramatic impact on magnetic properties of these compounds, and dimer-based materials, in particular, have been the subjects of many quantum-materials-directed studies in materials physics. Hexagonal oxide perovskites are of contemporary interest due to their potential for geometrical frustration of the ordering of magnetic moments or orbital occupancies at low temperatures, which is especially relevant to their significance as quantum materials. As such, several hexagonal oxide perovskites have been identified as potential candidates for hosting the quantum spin liquid state at low temperatures. In our view, hexagonal oxide perovskites are fertile ground for finding new quantum materials. This review briefly describes the solid state chemistry of many of these materials.

Quantum materials with strong spin–orbit coupling: challenges and opportunities for materials chemists

“…This symmetry element has made hexagonal perovskites of emerging interest because it again provides a structural template for geometric frustration, whilst the face sharing allows for unusually short M-M distances and small M-O-M bond angles that can dramatically influence their quantum properties. 91 Hexagonal perovskites effectively have a stacked structure, formed by the face-sharing multimers sharing corners with neighbouring multimers (which can be of of the same or different types), and this gives rise to extensive polymorphism derived from different stacking arrangements. AMO 3 materials can also show polymorphism between hexagonal and conventional perovskite structures -for example, the ambient pressure polymorph of SrIrO 3 is actually of the hexagonal 6H type, and the conventional GdFeO 3 -type polymorph mentioned previously is a metastable phase accessed through high-pressure synthesis.…”

“…In other words, the magnetic 'units' of the structure may no longer be the individual MO 6 octahedra but multimer 'molecules'. 91,95,96…”

Breaking the aristotype: featurisation of polyhedral distortions in perovskite crystals

“…to atomic coordinates and keeping track which atoms transformed to which atomic sites. The final 18 dimensional representationsΓ (18) (R) were constructed by taking a tensor product between three and six dimensional representationΓ (3) (R) ⊗Γ (6) (R).…”

Atomic Structure of the Initial Nucleation Layer in Hexagonal Perovskite BaRuO3 Thin Films

“…[ 2 ] In this regard, hexagonal perovskites provide an excellent platform for the investigation of a myriad of structure‐property relationships. [ 3–6 ]…”

“…2 In this sense, hexagonal perovskites serve as a platform for the investigation of a myriads of structure-property relationships. [3][4][5][6] In particular, Ba-based ABO 3 oxides, such as BaRuO 3 (BRO) and BaIrO 3 (BIO), have attracted considerable attention as prototypical hexagonal perovskites, as each polymorph exhibits unique electronic and magnetic properties. 7,8 In the case of the BRO system, the cubic phase (3C) (a = b = c = 4.005 Å , space group 221 (Pm3 ̅ m)) 9 was found to be a ferromagnetic metal with a transition temperature T c ≈ 60 K, whereas the 4H phase (a = b = 5.729 Å , c = 9.500 Å , space group 194 (P63/mmc)) 10 and 9R phase (a = b = 5.755 Å , c = 21.621 Å , space group 166 (R3 ̅ m)) 11,12 are paramagnetic.…”