23 research outputs found
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Floating Zone Growth of Pure and Pb-Doped Bi-2201 Crystals
In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi2Sr2CuOy (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal growth of Bi-2201 superconductors faces challenges due to intricate materials chemistry and the lack of knowledge of corresponding phase diagrams. Historically, a crucible-free floating zone method emerged as the most promising growth approach for these materials, resulting in high-quality single crystals. This review outlines the described methods in the literature and the authors’ synthesis endeavors encompassing Pb-doped Bi-2201 crystals, provides a detailed structural characterization of as-grown and post-growth annealed samples, and highlights optimal growth conditions that yield large-size, single-phase, and compositionally homogeneous Bi-2201 single crystals
TSFZ Growth of Eu-Substituted Large-Size LSCO Crystals
The travelling solvent floating zone (TSFZ) growth of Eu-substituted LSCO (La1.81−xEuxSr0.19CuO4, with nominal x = 0 ÷ 0.4) single crystals was systematically explored for the first time. The substitution of La with Eu considerably decreased the decomposition temperature. Optimal growth parameters were found to be: oxygen pressure 9.0–9.5 bars; Eu-free CuO-poor solvent (66 mol% CuO) with a molar ratio of La2O3:SrCO3:CuO = 4:4.5:16.5 and growth rate 0.6 mm/hour. The obtained single crystals were characterized with optical polarized microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. The solubility of Eu in LSCO appeared to be limited to x~0.36–0.38 under the used conditions. The substitution of La3+ with smaller Eu3+ ions led to a structural transition from tetragonal with space group I4/mmm for La1.81Sr0.19CuO4 (x = 0) to orthorhombic with space group Fmmm for La1.81−xSr0.19EuxCuO4 (x = 0.2, 0.3, 0.4), and to a substantial shrinking of the c-axis from 13.2446 Å (x = 0.0) to 13.1257 Å (x = 0.4). Such structural changes were accompanied by a dramatic decrease in the superconducting critical temperature, Tc, from 29.5 K for x = 0 to 13.8 K for 0.2. For x ≥ 0.3, no superconductivity was detected down to 4 K
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Flux Growth and Characterization of Bulk InVO4 Crystals
The flux growth of InVO4 bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V2O5:InVO4 = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO4 of typical size 0.5 × 1 × 7 mm3 were obtained using copper pyrovanadate (Cu2V2O7) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO4 crystals makes them excellent candidates for further study of their physical properties
Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO3
Ga for Mn substitution in multiferroic TbMnO has been performed in
order to study the influence of Mn-magnetic ordering on the Tb-magnetic
sublattice. Complete characterization of TbMnGaO ( = 0,
0.04, 0.1) samples, including magnetization, impedance spectroscopy, and x-ray
resonant scattering and neutron diffraction on powder and single crystals has
been carried out. We found that keeping the same crystal structure for all
compositions, Ga for Mn substitution leads to the linear decrease of and , reflecting the reduction of the exchange
interactions strength and the change of the Mn-O-Mn bond
angles. At the same time, a strong suppression of both the induced and the
separate Tb-magnetic ordering has been observed. This behavior unambiguously
prove that the exchange fields have a strong influence on the
Tb-magnetic ordering in the full temperature range below
and actually stabilize the Tb-magnetic ground state.Comment: 9 pages, 8 figure
Type II Bi 1- x W x O 1.5 + 1.5 x : a (3 + 3)-dimensional commensurate modulation that stabilizes the fast- ion conducting delta phase of bismuth oxide
The Type II phase in the Bi1 xWxO1.5 + 1.5x system is shown to have a (3 + 3)- dimensional modulated -Bi2O3-related structure, in which the modulation vector " ‘locks in’ to a commensurate value of 1/3. The structure was refined in a 3 3 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi1 xNbxO1.5 + x (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 ‘tetrahedra of octahedra’ and chains of corner-sharing WO6 octahedra along h110iF directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results
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Evidence for a percolative Mott insulator-metal transition in doped Sr2IrO4
Despite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping-induced insulator-to-metal transition is still a subject under intensive investigation. Here, we probe the nanoscale electronic structure of the Mott insulator Sr2IrO4−δ with low-temperature scanning tunneling microscopy and find an enhanced local density of states (LDOS) inside the Mott gap at the location of individual defects which we interpret as defects at apical oxygen sites. A chiral behavior in the topography for those defects has been observed. We also visualize the local enhanced conductance arising from the overlapping of defect states which induces finite LDOS inside of the Mott gap. By combining these findings with the typical spatial extension of isolated defects of about 2 nm, our results indicate that the insulator-to-metal transition in Sr2IrO4−δ could be percolative in nature
Solitonic lattice and Yukawa forces in the rare earth orthoferrite TbFeO3
The control of domains in ferroic devices lies at the heart of their
potential for technological applications. Multiferroic materials offer another
level of complexity as domains can be either or both of a ferroelectric and
magnetic nature. Here we report the discovery of a novel magnetic state in the
orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field.
This state has a very long incommensurate period ranging from 340 Angstrom at
3K to 2700 Angstrom at the lowest temperatures and exhibits an anomalously
large number of higher-order harmonics, allowing us to identify it with the
periodic array of sharp domain walls of Tb spins separated by many lattice
constants. The Tb domain walls interact by exchanging spin waves propagating
through the Fe magnetic sublattice. The resulting Yukawa-like force, familiar
from particle physics, has a finite range that determines the period of the
incommensurate state.Comment: 11 pages 14 figure
Rich Magnetic Phase Diagram of Putative Helimagnet SrFeO
The cubic perovskite SrFeO was recently reported to host hedgehog- and
skyrmion-lattice phases in a highly symmetric crystal structure which does not
support the Dzyaloshinskii-Moriya interactions commonly invoked to explain such
magnetic order. Hints of a complex magnetic phase diagram have also recently
been found in powder samples of the single-layer Ruddlesden-Popper analog
SrFeO, so a reinvestigation of the bilayer material SrFeO,
believed to be a simple helimagnet, is called for. Our magnetization and
dilatometry studies reveal a rich magnetic phase diagram with at least 6
distinct magnetically ordered phases and strong similarities to that of
SrFeO. In particular, at least one phase is apparently
multiple-, and the s are not observed to vary among the
phases. Since SrFeO has only two possible orientations for its
propagation vector, some of the phases are likely exotic multiple-
order, and it is possible to fully detwin all phases and more readily access
their exotic physics.Comment: 14 pages, 13 figure