Layered Cuprates Containing Flat Fragments: High-Pressure Synthesis, Crystal Structures and Superconducting Properties

High-pressure synthesis and crystal structures of the homologous series AuBa2(Ca,Ln)n-1CunO2n+3 (n = 1-4; Ln = rare-earth cations) are described. Their crystal structures and superconducting properties are compared with the corresponding members of the Hg-homologous series. Numerous cuprates containing flat structural fragments (CuO4, CO3 and BO3) synthesized mainly at high pressure are compared in terms of structural peculiarities and superconducting properties. Importance and future prospects of high-pressure application for the preparation of new superconducting oxides are discussed.

crystIT: complexity and configurational entropy of crystal structures via information theory

The information content of a crystal structure as conceived by information theory has recently proved an intriguing approach to calculate the complexity of a crystal structure within a consistent concept. Given the relatively young nature of the field, theory development is still at the core of ongoing research efforts. This work provides an update to the current theory, enabling the complexity analysis of crystal structures with partial occupancies as frequently found in disordered systems. To encourage wider application and further theory development, the updated formulas are incorporated into crystIT (crystal structure and information theory), an open-source Python-based program that allows for calculating various complexity measures of crystal structures based on a standardized *.cif file.

Large orbital polarization in nickelate-cuprate heterostructures by dimensional control of oxygen coordination

Artificial heterostructures composed of dissimilar transition metal oxides provide unprecedented opportunities to create remarkable physical phenomena. Here, we report a means to deliberately control the orbital polarization in LaNiO₃ (LNO) through interfacing with SrCuO₂ (SCO), which has an infinite-layer structure for CuO₂. Dimensional control of SCO results in a planar-type (P–SCO) to chain-type (C–SCO) structure transition depending on the SCO thickness. This transition is exploited to induce either a NiO₅ pyramidal or a NiO₆ octahedral structure at the SCO/LNO interface. Consequently, a large change in the Ni d orbital occupation up to ~30% is achieved in P–SCO/LNO superlattices, whereas the Ni e_g orbital splitting is negligible in C–SCO/LNO superlattices. The engineered oxygen coordination triggers a metal-to-insulator transition in SCO/LNO superlattices. Our results demonstrate that interfacial oxygen coordination engineering provides an effective means to manipulate the orbital configuration and associated physical properties, paving a pathway towards the advancement of oxide electronics.

In correlated materials, physical properties depend on orbital occupancy and polarization. Here, a way to control the oxygen coordination via dimensionality of superlattices is presented that results in the change of orbital occupancy by 30%, which is larger than what has been achieved by other methods.

Structural aspects of spin-chain and spin-ladder oxides

An overview is presented of the various oxidic compounds, that exhibit low-dimensional magnetic properties. These include spin-ladder and spin-chain compounds as well as compounds with a low-dimensional electronic band responsible for the magnetic order. The basic structures at room temperature are presented, and their dimensionality is discussed. The structural variations with temperature and magnetic field are analysed. Particular attention is given to the superstructures as they occur upon phase transitions involving the development of magnetic order and charge order. The consequences of these superstructures for the interpretation of the physical properties are reviewed.

Nitridocompounds of manganese: manganese nitrides and nitridomanganates

The chemistry of nitrides and nitridometalates is a rapidly growing field in solid state chemistry. This short review is intended to give a brief but comprehensive over-view on the compounds and phases formed with manga-nese, which cover an especially broad range of oxidation states. Furthermore, the present paper tries to put the ob-served structures and properties of the compounds into a broader context.

Crystal Growth and Structural Characterization of the New Ordered Palladates LnKPdO3 (Ln = La, Pr, Nd, Sm−Gd) and the Isostructural, Partially Cu-Substituted Palladate PrK(Cu0.14Pd0.86)O3

Single crystals of a new series of lanthanide-containing palladates, LnKPdO3 (Ln = La, Pr, Nd, Sm-Gd), and a partially copper-substituted palladate, PrK(Cu0.14Pd0.86)O3, were grown from potassium hydroxide fluxes. The compounds are all isostructural and crystallize in the C2/m space group with lattice parameters ranging from a = 13.4232(8) to 13.0212(2) A, b = 3.9840(2) to 3.9096(2) A, c = 7.4424(4) to 7.3209(9) A, and beta = 105.644(2) to 104.427(2) degrees . The crystal structure contains ordered slabs of LnO7- and KO7-capped trigonal prisms arranged in a complex network of face-, edge-, and vertex-shared polyhedra which, in turn, share edges with PdO4 square planes.

HREM study of the crystal chemistry of the alkaline-earth cupric oxides stabilized at high pressure

The crystal chemistry of the alkaline-earth cupric oxides stabilized at high pressure was studied by high-resolution electron microscopy. Two families of superconductors, (Ca1-ySry)1-xCuO2 and Srn+1CunO2n+1+delta (n = 1, 2), and one series of semiconductors, Srn-1Cun+1O2n, are reported. Their structural characteristics are systematically interpreted on the basis of the simple infinite-layer structure seen in SrCuO2. Microstructures and their relevance to high-Tc superconductivity are discussed, particularly in the alkaline-earth-deficient infinite-layer phase.