CuFeO 2 single crystals up to 50 mm in length and up to 10 mm in diameter were grown by the optical floating-zone method. Stoichiometric polycrystalline rods with a diameter of 6-12 mm were used as feed materials to produce crystals of sufficient size to be used as substrates for the growth of thin films of delafossites.For stable growth along the c-axis, low growth rates of 0.4 mm/h are necessary.Due to the incongruent melting behavior of CuFeO 2 , a stable melt zone requires adjustment of the lamp power during growth. The melting of CuFeO 2 is not simply incongruent because the thermodynamic equilibrium includes more than two solid phases and the melt; the gas phase is also involved. The crystals were characterized by X-ray diffraction and X-ray fluorescence measurements. from Catherinebourgh, Sibiria" -which instead he reported in the year 1873 to be composed from equimolar quantities of Cu + 2 O with the combination of Fe 3+ 2 O 3 , about 3.5% Al 2 O 3 [1]. This chemical composition can be written as Cu(Fe,Al)O 2 . The new mineral was given the name delafossite. In the years since Friedel's discovery a large number of other A + B 3+ O 2 compounds have become known that show basically the same structural features: BO 6 octahedra form layers that are stacked parallel to (001), and these edge-sharing octahedral sheets are connected along the [001] direction by linear O -A + -O bonds. Depending on details of the stacking sequence, the structures are usually either hexagonal or trigonal [2]. As an exception, Cu + Mn 3+ O 2 is monoclinic with space group C2/m [3]. Shannon et al. [4] revealed that not only copper and silver can acts as the A + element, but also other quite noble metals like palladium or even platinum. This is surprising because oxides of the platinum group metals are not only scarce and often unstable, but also the known platinum group binary oxides show oxidation states of 2+ or higher, e.g. PdO, PdO 2 , PtO, PtO 2 , PtO 3 , and not Pt 1+ as occours in Pt-containing delafossites.Oxide materials based on the ABO 2 delafossite structure are of particular interest due to the novel properties that accompany their cation variation at A and B sites. These properties are of interest to fundamental science [5,6,7,8,9] as well as applications [10]. Usually, the semiconductor delafossites consist of Ag or Cu at the A-site and several trivalent cations like Al, Fe or Ga at the B-site. Important among the semiconducting delafossites is CuAlO 2 with its relatively high mobility for a p-type transparent conducting oxide [11]. Pd-and Pt-based compounds (for A + ) are metallic delafossite oxides where B-site cations are transition metals like Co, Cr or Rh [4,12,13]. Among these, the growth of single crystalline PdCoO 2 has become of interest due to its ultra-high conductivity at room temperature. Recently an in-plane resistivity ρ ab = 2.6 µΩ·cm at 295 K was measured for sub-mm-sized PdCoO 2 crystals, which makes this material the most conductive oxide known, comparable to the best metallic conductors Ag, Cu, Au a...

Strain-engineering is a powerful means to tune the polar, structural, and electronic instabilities of incipient ferroelectrics. KTaO3 is near a polar instability and shows anisotropic superconductivity in electron-doped samples. Here, we demonstrate growth of high-quality KTaO3 thin films by molecular-beam epitaxy. Tantalum was provided by either a suboxide source emanating a TaO2 flux from Ta2O5 contained in a conventional effusion cell or an electron-beam-heated tantalum source. Excess potassium and a combination of ozone and oxygen (10% O3 + 90% O2) were simultaneously supplied with the TaO2 (or tantalum) molecular beams to grow the KTaO3 films. Laue fringes suggest that the films are smooth with an abrupt film/substrate interface. Cross-sectional scanning transmission electron microscopy does not show any extended defects and confirms that the films have an atomically abrupt interface with the substrate. Atomic force microscopy reveals atomic steps at the surface of the grown films. Reciprocal space mapping demonstrates that the films, when sufficiently thin, are coherently strained to the SrTiO3 (001) and GdScO3 (110) substrates.

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