High pressure synthesis & characterization of functional materials

Resume : Superconductivity under high pressure has been paid the considerable attention. In particular superconductivity in H2S at 200 K under 150 GPa was discovered using a diamond anvil cell (DAC) [1]. It is predicted that if we can measure the resistivity under extremely higher pressure above 300 GPa, superconductivity at room temperature in hydrogen could be observed [2]. However, resistivity measurement under high pressure is quite difficult because of the small sample sizes (< 100 μm) and the deformation of electrodes by compression. The development of an innovative technique for the transport measurements under high pressure is required. In this study, we have developed a DAC specialized for the resistivity measurements under high pressure [3]. The key components are two kind of special diamonds. One is a heavily boron-doped metallic diamond as an electrode [4,5]. When the boron concentration exceeds 3×1020 cm-3, diamond shows metallicity and superconductivity at low temperature. The diamond electrodes were nanofabricated by using combination of a microwave-assisted plasma chemical vapor deposition method and an electron beam lithography technique. The other is a nano-polycrystalline diamond (NPD) as a bottom anvil [6]. The NPD consists of nanoparticle, leading to the high mechanical hardness. The resistivity measurements can be easily performed by the DAC using the microscale boron-doped diamond electrodes fabricated on the NPD anvil. The resistivity measurements of Pb and iron-based superconductor FeSe were demonstrated under various pressures. For Pb, the resistivity exhibited metallic behavior, and suddenly dropped to zero at all pressures. The Tc was gradually decreased from 7.2 K to 4.4 K with increase of applied pressure up to 8 GPa. dTc/dP showed good agreement with previous report [7]. The maximum pressure was above 30 GPa using the culet size of 0.4 mm. After several measurements, there were no cracks in the metallic diamond electrodes. The resistivity measurements under extremely high pressure above 300 GPa is expected by developed DAC because the microscale diamond electrodes allows us to use smaller culet. References: 1. A. P. Drozdov, M. I. Eremets, I. A. Troyan, V. Ksenofontov and S. I. Shylin, Nature 525, 73(2015). 2. N. W. Ashcroft, Phys. Rev. Lett. 21, 1748 (1968). 3. R. Matsumoto, Y. Sasama, M. Fujioka, T. Irifune, M. Tanaka, T. Yamaguchi, H. Takeya and Y. Takano, arXiv : 1603.05452 (2016). 4. Y. Takano, M. Nagao, I. Sakaguchi, M. Tachiki, T. Hatano, K. Kobayashi, H. Umezawa and H. Kawarada, Appl. Phys. Lett. 85, 2851 (2004). 5. T. Yokoya, T. Nakamura, T. Matsushita, T. Muro, Y. Takano, M. Nagao, T. Takenouchi, H. Kawarada and T. Oguchi, Nature 438, 647 (2005). 6. T. Irifune, A. Kurio, S. Sakamoto, T. Inoue and H. Sumiya, Nature 421, 599 (2003). 7. A. Eiling and J. S. Schilling, J. Phys. F: Metal Phys. 11, 623 (1981).

Resume : Recently with the opening of the Xpress beamline [1], the high pressure powder diffraction user community of the Elettra synchrotron facility have a dedicated experimental set up at their disposal. This new beamline is part of a scientific partnership between India and Italy under a project administered through the Indian Institute of Sciences (IISc) Bangalore, for the development of a macromolecular and a high pressure x-ray diffraction facilities, respectively XRD2 and Xpress. A multipole superconducting wiggler (SCW) is the source of these two beamlines. A liquid nitrogen cooled silicon single crystal (cut along the (111) direction) hosted in the splitter chamber in the Front-End section intercepts the beam from the source (SCW) and directs it to the focusing mirror of the Xpress at a fixed energy of 25 keV. At this energy, the SCW provides a factor of 14 higher photon flux compared to the permanent magnet wiggler of XRD1, the existing diffraction beamline. The beam is focused using a toroidal mirror of 1.4 m long and 2.9 mrad grazing angle with a Pt coating to achieve 80% reflectivity at 25 keV. Focused beam from the mirror is further optimized by collimators (presently 80 micron diameter) to have intense and well defined monochromatic beam required for the high pressure x-ray diffraction experiments. On-line pressure monitoring is achieved through a ruby fluorescence microscope connected side-by-side to the final beam collimator stage. The present experimental stage is equipped to host room temperature - high pressure powder diffraction measurements using various kinds of Diamond Anvil Cells (DAC) in the pressure range 0-50 GPa. An image plate MAR345, with a controllable linear movement along the beam direction at two fixed vertical positions is available for recording the diffraction pattern. A variable temperature (100 – 300 K) capillary powder diffraction stage is also available to the users. From the beginning of 2016, the beamline is open to users for proposal submission. Already several user groups have successfully performed high pressure powder diffraction experiments collecting excellent data on a variety of systems. Achieving the best possible hydrostatic pressure conditions are important to further advance the performance of the beamline. There is a significant progress is in this direction with the addition of a He gas loader (Sanchez Technologies) by the end of 2016. Thanks to this huge investment by the collaborating Indian counterpart, there will be a substantial upgrade in the high pressure infrastructure of the beamline, opening new avenues for the further performance. [1] http://www.elettra.eu/elettra-beamlines/xpress.html

Resume : Material science and nanotechnology are two of the main research fields to take up future challenges of Europe such as alternative energy sources and energy storage or biomedical and pharmaceutical materials. The scientific problems coming up in this fields have become more and more complex in the recent years and require an ever increasing number of instrumental and analytical techniques and disciplines. Such complexity requires the availability of expertise as well as open access to a wide range of probing techniques and many different complementary instruments. CERIC-ERIC research infrastructure was developed to face this challenge and to make a wide variety of instruments available through free open access based on a peer-review process. CERIC stands for Central European Research Infrastructure Consortium and is a distributed research infrastructure, unifying several national institutions under one roof. This multinational facility was set up as a European Research Infrastructure Consortium (ERIC) and brings together the best research facilities from Austria, Croatia, Czech Republic, Hungary Italy, Poland, Romania and Slovenia. All partners offer free and open access for excellent researchers all over the world to a set of complementary, cutting-edge instrumentation. The instruments can be accessed with one single proposal, submitted through a joint portal, where the calls are published twice per year CERIC-ERIC comprises synchrotron radiation, neutron radiation, microscopic techniques, ion-beam analysis methods and NMR. This talk will present CERIC, its instruments and possibilities for researchers in the field of material science.

Resume : Carbon nanomaterials, such as nanotubes, fullerene, provide us ideal carbon sources to study novel phase and design new carbon materials induced by high pressure. A novel carbon material has been recently reported from compressing C60 solvates (C60/m-xylene) and the obtained high pressure phase---the ordered amorphous carbon cluster (OACC) structure, breaks our inherent understanding of the categorization of various phases and adds a new member to the list of structures [Wang et al, Science 337, 825 (2012)]. Here, another example of OACC is also presented from compressing C70/m-xylene in which amorphized and highly compressed C70 units act as building blocks. A new phase transition occurs in the compression process, which is very different from compressing C60/m-xylene, indicating OACC structure can be tuned by changing the initial fullerene molecules. The deformation of fullerene molecules under pressure and the formation mechanism of the high pressure hard phase have also been revealed. Our study extends the OACC structure to larger fullerenes and suggests a universal rule for the high pressure behaviors of lower symmetry systems of solvated fullerenes [Cui et al, Adv Mater 26, 725 7(2014) ]. We also have compressed a series of intercalated fullerene solvated, pre-designed by selecting various solvents with special features and found that solvents with hexagons are able to form OACC structures and promote π-electron rehybridization between high pressured induced amorphous cluster and solvents under pressure (Yao etal, Adv Mater 27, 3962 (2015).

Resume : Perovskites constitute the most abundant group of minerals [1] and are one of the most studied class of materials due to the diversity of technologically attractive phenomena these materials display. Perovskites’ crystal chemistry is very rich, particularly under non-ambient conditions [2]. Recently, a subgroup of perovskite oxides, namely the A-site deficient Ln1/3MO3 (Ln = La, Pr, Nd, M = Nb, Ta) oxides, was found to undergo irreversible pressure induced amorphization (PIA) at modest pressures around 14.5 GPa [3, 4] for niobates (La1/3NbO3) and around 18.5 GPa for tantalates Ln1/3TaO3 [4, 5]. PIA is subject of intensive research, since the observation of this phenomena in a number of simple materials including ice [6] and α-quartz [7] and in materials with special interest to geophysics such as Fe2SiO4 [9] and Mg2SiO4 [8]. In order to probe the mechanism of PIA in La 1/3 NbO 3 we have used the local structure using x-ray absorption spectroscopy (XAS) at Nb K-edge. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopies have the added advantage over diffraction that these techniques can be readily applied also to the amorphous systems. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb–O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb–O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb5+ towards Nb4+ above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb–O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at ∼14.5 GPa[9]. References [1]Tejuco L G and Fierro J L G (ed) 1993 Properties and Applications of Perovskite-Type Oxides (New York: Dekker) [2] Navrotsky A and Weidner D J (ed) 1989 Perovskite: a Structure of Great Interest to Geophysics and Material Science (Washington, DC: American Geophysical Union) [3] Noked O et all, J. Non-Cryst. Solids, 357, 3334 (2011) [4]Noked O et al Phys. Chem. Miner., 41, 439 (2014) [5] Noked et al. J. Solid State Chem., 202, 38 (2013) [6]Mishima O et al. Nature, 310, 393 (1984) [7]Hemley R J et al Nature, 334, 52 (1988) [8]Williams Q et al., J. Geophys. Res., 95, 21549 (2010) [9]Marini C et al. J. Phys.: Condens. Matter, 28, 045401 (2016)

Resume : Topological insulators (TIs) represent a newly discovered phase of matter with an insulating bulk state but a topologically protected metallic surface state due to time-reversal symmetry and strong spin-orbital interactions. The discovery of TIs in V2VI3-type compounds Bi2Se3 and Bi2Te3 opened a new era in fundamental topological physics, and attracted much attention in experimental and theoretical investigations [1,2]. The crystal structure and transporting properties of three typical V2VI3-type compounds (Bi2Se3, As2Te3, BixSb2-xTe3) under high pressure were investigated by experimental and theoretical methods in this work. Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of Bi2Se3 have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (R-3m) to monoclinic phase (C2/m) and eventually to a high pressure body-centered tetragonal phase (I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into an I4/mmm structure rather than the recently reported disordered body-centered cubic (BCC) phase [3]. Although possessing the similar chemical content to Bi2Te3 and Sb2Te3, the V2VI3-type compound As2Te3 adopts a 6-fold monoclinic structure (phase α; C2/m) at ambient conditions. Upon compression, α-As2Te3 transforms into phases α' and α" at about 5.09 and 13.2 GPa, respectively, with two isostructural phase transitions. From 13.2 GPa, As2Te3 starts to transform into phase γ, with one first-order monoclinic to monoclinic crystal structural phase transition. According to the DFT calculations and electrical resistance measurements, the structural transitions in the compression process induce transformations from an insulator (phase α) across a semimetal (phase α') into a metal (phases α" and γ) [4]. Recently, in Cr-doped (Bi/Sb)2Te3 thin films, the quantum anomalous Hall (QAH) effect was observed, which showed that the TIs keep as a hot topic in physical and material research fields [5]. The crystal structure and corresponding physical properties of doped V2VI3-type compounds such as BixSb2-xTe3 under high pressure was being investigated in our research group. Reference: [1] J. E. Moore, The birth of topological insulators. Nature 464, 194 (2010). [2] X. L. Qi & S. C. Zhang, Topological insulators and superconductors. Rev. Mod. Phys. 83, 1057 (2011). [3] Zhenhai Yu et al. Structural phase transitions in Bi2Se3 under high pressure. Sci. Rep. 5, 15939 (2015). [4] Jinggeng Zhao, Liuxiang Yang, Zhenhai Yu et al. Structural Phase Transitions and Metallized Phenomena in Arsenic Telluride under High Pressure, Inorganic Chemistry, 55, 3907 (2016). [5] Q. K. Xue, et al. Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator, Science, 340, 167 (2013).

Resume : This article focuses on the formation of composite materials based on α-AlB12 and AlB12C2 AlB40C4 under hot pressure (30 МPа) and high quasihydrostatic pressure (2 GPа) conditions at 1200-2100 оС. The interrelations between materials properties and structures are under the consideration. The results of the present study allowed us to conclude that the fracture toughness of α-AlB12 (98 wt.%, porosity 1.59%, density2.58 g/cm3) was lower than that of the AlB12C2–based composites (AlB12C2=70 wt.% BN=14 wt.% Al2O3=16 wt.%, porosity 5%, density2.42 g/cm3) prepared by hot pressing (at 30 MPa). The fracture toughness (estimated under 49 N-load) of AlB12C2 –based composite was 7.6 MPа•m¹/² and the material Vickers hardness was about 20.1 GPа while the fracture toughness of α-AlB12 prepared under the same conditions was much lower: K1C = 4.2±0.5 MPа•m¹/² while the hardness was somewhat higher HV = 24.1 GPа. The fracture toughness of α-AlB12 sintered under high pressure (2 GPa) conditions was as well lower than that of AlB12C2. Addition of carbon (17 wt.%) to α-AlB12 and hot pressure synthesis leads to the formation of the composite material (AlB12C2=86wt.% and AlN_H=14wt.%, porosity 0.13%, density 2.7 g/cm3) with K1C = 5.9±1.4 MPа•m¹/² and Vickers hardness HV = 23.6±2.8 GPа. The material which according to the Rietveld of X-ray pattern refinement contains 99 wt.% of AlB40C4 (synthesized at 30 МPа) with density (2.64 g/cm3) which was somewhat higher than the theoretical one (2.64 g/cm3 ) demonstrated under the 49 N load 23.5 GPа hardness and 3.7 МPа•m¹/² fracture toughness. It should be mentioned that the higher density can be the result of Al2O3 presence in the material (as SEM study showed). The work was performed in the framework of the NATO Science for Peace G7050 project.

Resume : Complex oxide heterostructure has emerged as a new interesting playground for condensed matter physics and material science. By combining multiple active degrees of freedom of transition-metal oxides, the correlated electron phenomena, already existing in the mother compounds, can be further controlled and hopefully utilized. While the experimental parameters such as dimensionality and epitaxial strain are basically controllable, the identification of the atomic arrangement and its effect on the material property is difficult to be identified. First-principles calculation can play a crucial role in this situation. Here we take a typical Mott insulating system LaTiO3 as an example and discuss how its electronic and magnetic property change when confined in the superlattice geometry. By increasing the level of approximation to describe on-site electronic correlation, we try to understand the recent experimental data and to suggest a new possibility. In particular, we discuss the characteristic electronic structure caused by the confinement, the strain-controlled magnetic ground state, and the possible orbital fluctuation at the phase boundary. Emphasis will be laid on the capability of first-principles calculation to collaborate with experiment especially on the subtle situation in which the conventional measurement techniques may not work well.

Resume : Low temperature superconduction based on Nb-Ti alloys are currently widespread, they used in power engineering, transport, telecommunications engineering, medicine and other directions of application. That superconduct material has high mechanical properties and it is low cost. It have theoretical limit of the critical current density Ic of 1011 A/m2 in field of 5T at 4.2K, but near 4% of this value is achieved in real exploitation. It is well known that functional property Nb-Ti alloys are determined by amount of structural defects basically α-Ti precipitations and grain boundaries, what are pinning centers. But in that time another approaches, in particular, deformation and heat treatment leads to formation of pinning centers are not well study. In this work we have presented the results of investigation of effect of severe plastic deformation, such as equal channel multiple angular pressing (up to 32 cycles, true strain 26.24) and extrusion (1 cycle, true strain 2.2) under high pressure with subsequent heat treatment on structure, phase composition and critical current density. TEM and HRTEM identify wide range of structural changes: splitting of initial phase and appearing of new small precipitations, formation of deformation martensite, appearance of bending crystal planes, increasing of inhomogeneity of chemical composition and grains fragmentation that improve under heat treatment. Processing conditions, which lead to an increase of critical current density and mechanical properties performance of superconductors baser on Nb-Ti alloys.

Resume : The BiS2–based materials possess a layered structure with superconducting BiS2 bilayers intercalated by insulating spacer layers. Superconductivity in this class of materials is extremely susceptible to external stimuli like doping, chemical pressure and hydrostatic pressure. Here we report case studies in which, by means of X-ray absorption spectroscopy, we have studied the effect of these parameters on local structure and local electronic states. In particular CeOBiS2 has been chosen to study the effect of F-doping on structural and magnetic degrees of freedom [1,2]. The effect of chemical pressure is studied by changing mean rare earth size in REO0.5F0.5BiS2. In particular the local effect of substitution of the rare-earth with Ce, Nd, Sm encompassing a wide range of ionic radius have been investigated [3]. For the case of pressure we take example of EuBiFS2 in which superconductivity is induced by self-doping coming from Eu valence fluctuation. When pressurized, this system shows an interesting p-T phase diagram with Tc going from 0.3 K at ambient pressure up to 9 K at 1.5 GPa. By means of X-ray absorption spectroscopy as a function of high pressure and temperature we observed the multiple valence state of Eu in EuBiFS2 and its evolution across the p-T phase diagram [4]. [1] T. Sugimoto et al, Phys. Rev. B 89, 201117 (R) (2014). [2] E. Paris et al, J. Phys. Condens. Matter 26, 435701 (2014). [3] Y. Mizuguchi et al, Phys. Chem., Chem. Phys. 17, 22090-22096 (2015). [4] E. Paris et al, manuscript in preparation.

Resume : Many macroscopic characteristics of ferroelectric materials are directly related to the physical properties of domains and domain walls. Therefore, it is crucial to investigate structure, size and orientation of domains and domain walls on the nanoscale in order to get a fundamental understanding of formation mechanisms and functionality of domain walls. Especially, periodic structures with monoclinic symmetry are of particular interest. Their formation has been predicted for (K,Na)NbO3 thin films grown under anisotropic in-plane strain. In this study, K0.7Na0.3NbO3 thin films were grown under anisotropic lattice strain on (110) TbScO3 substrates by metal-organic chemical vapor deposition. By means of piezoresponse force microscopy and x-ray diffraction monoclinic domains were identified with a lateral polarization component collinear with the ±[-1 10]pc direction of the pseudocubic (pc) unit cell of the film and periodically changes by 180° in adjacent domains. The monoclinic symmetry of the domains is controlled by the elastic anisotropy of K0.7Na0.3NbO3 and the anisotropic lattice strain, which is highly compressive in one in-plane direction and weakly tensile in the corresponding orthogonal direction. With increasing thickness a 90° rotated domain variant occurs where the lateral polarization vector is aligned along ±[110]pc . Domain size and piezoelectric coefficient will be discussed in terms of film thickness and strain state.

Resume : Functional ferromagnetic shape memory materials attract an increasing attention of researchers due to their unusual deformation behavior resulting in a reversible size change under the influence of temperature, applied external stresses, magnetic fields, and their combination, demonstrating the effects of shape memory, pseudoelasticity or superelasticity, plasticity of transformation, magnetoelastic deformation, etc. The study of deformations induced by fields of external stresses was conducted for ferromagnetic iron-based alloys, among which the most interesting are Fe-Pd, Fe-Pt and Fe-Ni-Co-Ti, Fe-Ni-Co-Ti-Cu [1]. The effect of preliminary plastic deformation and following aging of quenched austenite on characteristics of thermoelastic martensite transformation, as well as on elastic deformation behaviour of martensite and austenite phases were investigated in this work to develop regimes of thermomechanical treatment (TMT) and to improve the mechanical properties of Fe-Ni-Co-Ti shape memory alloys. The characteristic temperatures of martensitic transformation, mechanical characteristics, such as microhardness, ultimate tensile strength, and ductility of martensite and austenite phases have been determined. All these parameters non-monotonously vary with the increase of plastic deformation. Plastic deformation at drawing results in stabilization of austenite. [1] A. Titenko, L. Demchenko. Superelastic Deformation in Polycrystalline Fe-Ni-Co-Ti-Cu Alloys. Journal of Materials Engineering and Performance, (2012) Vol 21 (10), p. 2011-2206, doi: 10.1007/s11665-012-0406-x

Resume : We performed high pressure X-ray Diffraction experiments on nanoparticles of pure tin oxide (particle size 30nm) and Fe doped tin oxide (particle size 18nm). The pure tin dioxide (SnO2) nanoparticles structural behavior was studied up to 32 GPa while the Fe-doped tin dioxide (formula: Fe0.1Sn0.9O2) nanoparticles were studied up to 19 GPa with X-ray synchrotron radiation. We have found that both samples present a structural phase transition from the tetragonal rutile-type P42/nmn at ambient temperature to a CaCl2-type structure (space group Pnnm) at ~10GPa. Additionally, pure tin oxide presented a fluorite-type phase transition at ~25 GPa (space group Fm3m). The cell constants, as well as the bulk modulus and bulk modulus first derivative are reported.

Resume : Nickel-chromium steels have been one of the most popular types of medical biomaterials, used in orthopedic and dental techniques, for many years. However, their shortcomings are low resistance to corrosion and tribological wear, as well as toxicity due to the presence of nickel. Wear products generated by degradation may cause many diseases (inflammation, allergic reaction, metalosis), often resulting in failure of medical therapy. This study presents the results of in vitro tests of fretting and fretting-corrosion processes conducted on 316L implantation steel. Special attention was paid to the role of oxygen in these processes. Friction tests were conducted in an aqueous environment using a pin-on-disc fretting tester, combined with a set for electrochemical testing. Observations of samples' surface morphology under a microscope made it possible to determine the volume of material losses and thus evaluate fretting wear. Obtained test results indicate a significant influence of oxygen on mechanisms of wear processes. It was observed that intensification of friction oxidation processes has an unfavorable impact on the stability of friction resistance. Wear products accumulate in the friction zone and accelerate destruction of steel by acting as an abrasive (so-called secondary wear). Adhesive wear mechanisms are dominant in deoxidized solutions. Conducted tests are exploratory in nature and oriented, in particular, towards gaining a better understanding of the destruction mechanisms of constructional biomaterials and thus extending the time of their reliable operation in medical applications.

Resume : The results of mechanical tests of polycrystalline ferromagnetic Fe-Ni-Co-Ti alloy with both martensitic and austenitic structure of phase of cooling and/or stress, including two-phase region, at uniaxial stretching in a wide temperature range are presented in this work. The alloy specimens were preliminarily thermo-mechanically treated with various regimes, which consisted of multiple drawing operations through draw plate with diameters from 20 mm to 5 mm, subsequent quenching in water from 1373 K and aging at 923 K for 5, 10, 20 minutes. The enough high level of superelastic deformation and one-way shape memory effect were achieved in the alloy. It was experimentally established that preliminary thermomechanical treatment, which consists of drawing with compression degree 7,4÷22,5%, following quenching and aging at 650C for 5-10 min, favours the deformation of initial alloy on the channels of phase and twinning plasticity in the testing temperature range of Ms

Resume : The authors have succeeded in the crystal growth of a room-temperature multiferroic BiFeO3 by a laser-diode-heated floating zone (LDFZ) method newly developed by themselves [1,2]. In this method, multiple LDs are used as a heat source instead of lamps that are commonly used for commercial FZ furnaces, and local and homogeneous heating on the molten zone by circularly aligned LDs is realized, which stabilizes the crystal growth of incongruently melting materials such as BiFeO3. Although the ferroelectric domains in BiFeO3 accompanied by the lattice distortions tend to tangle by inhomogeneous thermal strain in general, a single crystal of BiFeO3 consisting of almost single ferroelectric domain can be grown by the LDFZ technique, which is an evidence for homogeneous heating with negligible disturbance in the temperature distribution. In a single ferroelectric domain of BiFeO3 coexist three kinds of helical antiferromagnetic structures (magnetic domains). Since their propagation vectors differ from each other by 120 degrees, they are distinguished by the anisotropic magnetic susceptibility of the helical magnetism. The authors found that anisotropic magnetic susceptibility changes by the application of magnetic fields larger than 30 kOe, which shows populations of magnetic domains change and magnetic domains can be manipulated by high magnetic fields. References: [1] T. Ito et al., J. Cryst. Growth 363, 264 (2013). [2] T. Ito et al., Cryst. Growth Des. 11, 5139 (2011).

Resume : Electronic, magnetic and structural phase transitions in RNiO3 (R = Y3+, Tl3+ and 4f rare-earth) perovskites are of interest for condensed matter scientists since a long time. Especially, the rare-earth nickelates were studied extensively because of an existence of a metal-to-insulator transition (MIT). The transition temperature (TMIT) depends on the size of R3+ metal ions and varies between 130 K (for Pr) and 600 K (for the smallest Lu). The compound with the largest R3+ ion - LaNiO3 remains in contrast metallic in the whole temperature range. In nickelates, besides the MIT, there are also other interesting properties observed or theoretically suggested as thermochromicity, multiferroelectricity or even high-Tc superconductivity. Up to now, a stabilization of the high Ni3+ oxidation state in these compounds, especially for those containing small (Lu) to medium (Dy) rare earth ions, was achieved using very high oxygen pressures (20-60 kbar) during the synthesis. Such conditions can only be applied for samples with limited mg-range weight and therefore, were an important drawback for further progress in these research filed. We could show that most of the nickelates of interest in this work can be obtained at much lower pressure. Taking advantage of our high oxygen pressure system (Pmax = 2 kbar), we have recently succeeded to synthesize a series of compounds in gram-quantities ranging from LaNiO3 up to LuNiO3.

Resume : Optical Floating-zone (FZ) technique using focused light as a heating source is widely used to crystallization of many different materials. However, a necessity to use transparent crystallization chambers limits the accessible maximum gas pressure during growth to usually 10 bars. This, however, cannot be sufficient for crystallization of materials with high vapour pressures or decomposing when the pressure of an active gas component (e.g. oxygen in case of oxides) is not high enough. In this work we will show examples of such cases and report on our crystallization studies of CuO and spin ladder superconducting cuprate Sr14-xCaxCu24O41. For both materials crystal growth was performed in modified in our laboratory, commercial (CSC Japan) mirror furnace capable to work under 35 bar of oxygen. Availability of instruments allowing application of oxygen pressures up to 150 bar and growth temperatures up to 3000oC (ScIDre GmbH Dresden) creates new promises for the crystal growth by the FZ which will be also shortly discussed.

Resume : The manufacturing temperature of superconducting MgB2 can vary between 873 and 1423 K, and also depends on the applied pressure. The application of high pressure during manufacturing of bulk MgB2 leads an increase in critical current density (Jc). The higher synthesis temperatures lead to higher Jc values, especially at low and medium external magnetic fields, but also to lower Jc at high fields. At low manufacturing temperatures and high pressures, higher critical magnetic fields Bc2 and Birr can be achieved. It is accompanied by a shift of grain boundary pinning toward point pinning with increasing synthesis temperature. At temperatures of 873-1073 K, superconducting MgB2 can be prepared in a wide range of pressures from 0.1 MPa up to 2 GPa, with different densities and rather high critical currents. According to X-ray diffraction data materials prepared under high pressure (2 GPa) contain only MgB2 and MgO phases and in that, synthesized at low temperatures (1073 K and below), some Mg (unreacted) and MgH2 can be present as well. Samples prepared at 873 K, 2 GPa from magnesium and boron with an increased concentration of carbon (3.5 wt.% C) despite low connectivity of about 18 % exhibited high jc at high magnetic fields and high upper critical magnetic fields Bc2 (22 K) = 15 T, extrapolated Bc2 (0 K) = 42.1 T.