Growth of CuFeO2 single crystals by the optical floating-zone technique

Abstract

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...

Crystal growth and thermodynamic investigation of Bi2M2+O4 (M = Pd, Cu)

“…From our previous investigations on copper oxide compounds, it is known that copper oxide based melts always contain Cu + and Cu 2+ . [31][32][33][34] of the Bi 2 CuO 4 compound appears at 855°C and is connected with a mass loss of Δm/m = −0.41% in the associated TG curve. Bi 3+ can be considered to be stable under the experimental conditions used here.…”

Temperature-dependent optical properties of CuFeO2 through the structural phase transition

“…The single crystals were characterized using X-ray powder diffraction and magnetization measurements. 22,23 Besides the higher cost and longer growth process, the advantages of using CuFeO 2 single crystal for research are high phase purity, excellent crystallinity, and easy to study the anisotropic behavior of the materials compared to CuFeO 2 polycrystalline powder. Moreover, X-ray powder diffraction profile revealed that the as-grown and one year aging samples exhibited almost identical pattern, implying the good stability for CuFeO 2 .…”

Nonreciprocal Transport in a Rashba Ferromagnet, Delafossite PdCoO2

“…Our study of nonreciprocal transport at the ferromagnetic surface of an ultrathin PCO film suggests that delafossite heterostructures will provide a fruitful chance to deepen our knowledge about Rashba-related phenomena, and related efforts on the stabilization of high-quality delafossite films have been progressing. 31,32 The unique coexistence of surface ferromagnetism and Rashba spin−orbit coupling offers exciting opportunities for spin−orbitronics and to test theoretical predictions such as skyrmionic spin textures, 18 signatures of which may have been observed from topological Hall effect in ref 29. The delafossite family comprises several other interesting compounds, including good thermoelectrics and multiferroics such as CuFeO 2 33 or AgCrO 2 .…”