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283 results on '"Klimm, Detlef"'

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

Author

Wolff, Nora, Klimm, Detlef, Habicht, Klaus, and Fritsch, Katharina

Subjects
*CRYSTAL growth, *VALENCE fluctuations, *PHASE equilibrium, *X-ray powder diffraction, *CALORIMETRY, *TERNARY phase diagrams, *SPECIFIC heat
Abstract

Phase equilibria that are relevant for the growth of Bi2MO4 have been studied experimentally, and the ternary phase diagrams of Bi2O3–PdO2–Pd and Bi2O3–Cu2O–CuO and its isopleth section Bi2O3–CuO were redetermined. It is shown that every melting and crystallization process is always accompanied by a redox process at the phase boundary and that for both title compounds, the valence of the transition metal is lowered during melting. Vice versa, during crystal growth, O2 must be transported through the melt to the phase boundary. Based on these new insights provided by our thermodynamic studies, Bi2CuO4 single crystals with a length of up to 7 cm and a diameter of 6 mm were grown by the OFZ technique to be used for investigations of magnetic, electronic and thermal transport properties. The grown crystals were characterized by powder X-ray diffraction, Laue, magnetization and specific heat measurements. [ABSTRACT FROM AUTHOR]

Published
2021
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104. Ultra-wide bandgap, conductive, high mobility, and high quality melt-grown bulk ZnGa2O4 single crystals

Author

Galazka, Zbigniew, primary, Ganschow, Steffen, additional, Schewski, Robert, additional, Irmscher, Klaus, additional, Klimm, Detlef, additional, Kwasniewski, Albert, additional, Pietsch, Mike, additional, Fiedler, Andreas, additional, Schulze-Jonack, Isabelle, additional, Albrecht, Martin, additional, Schröder, Thomas, additional, and Bickermann, Matthias, additional

Published
2019
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105. Thermal anomalies and phase transitions in Pb2Sc2Si2O9and Pb2In2Si2O9

Author

Gogolin, Mathias, Murshed, M. Mangir, Bayarjargal, Lkhamsuren, Klimm, Detlef, and Gesing, Thorsten M.

Abstract

Pb2Sc2Si2O9and Pb2In2Si2O9, respectively, the scandium and indium containing structural analogues of the mineral kentrolite are grown by spontaneous crystallization from a PbO flux. The corresponding polycrystalline powder samples are synthesized by conventional solid-state approach. The compounds are thoroughly characterized using temperature-dependent single crystal and powder X-ray diffraction, heat capacity measurements, second harmonic generation experiments and Raman spectroscopy. At ambient conditions, both compounds crystallize in the non-centrosymmetric Pna21space group and undergo phase transitions to the centrosymmetric Pbcnspace group at elevated temperatures. The Pbcninto Pna21phase transitions are complemented by the signals of the temperature-dependent second harmonic generation. The specific heat capacity exhibits distinct cusp, supporting the λ-type second-order phase transition. The temperature dependency of some selective Raman modes further complements the findings, showing softening and hardening of the phonons across the phase transitions.

Published
2021
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112. Large-lattice-parameter perovskite single-crystal substrates

Author

Uecker, Reinhard, primary, Bertram, Rainer, additional, Brützam, Mario, additional, Galazka, Zbigniew, additional, Gesing, Thorsten M., additional, Guguschev, Christo, additional, Klimm, Detlef, additional, Klupsch, Michael, additional, Kwasniewski, Albert, additional, and Schlom, Darrell G., additional

Published
2017
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113. Ultra-wide bandgap, conductive, high mobility, and high quality melt-grown bulk ZnGa2O4 single crystals.

Author

Galazka, Zbigniew, Ganschow, Steffen, Schewski, Robert, Irmscher, Klaus, Klimm, Detlef, Kwasniewski, Albert, Pietsch, Mike, Fiedler, Andreas, Schulze-Jonack, Isabelle, Albrecht, Martin, Schröder, Thomas, and Bickermann, Matthias

Subjects
SINGLE crystals, SEMICONDUCTORS, BAND gaps, ELECTRONS, ELECTRICAL resistivity, ELECTRONICS
Abstract

Truly bulk ZnGa2O4 single crystals were obtained directly from the melt. High melting point of 1900 ± 20 °C and highly incongruent evaporation of the Zn- and Ga-containing species impose restrictions on growth conditions. The obtained crystals are characterized by a stoichiometric or near-stoichiometric composition with a normal spinel structure at room temperature and by a narrow full width at half maximum of the rocking curve of the 400 peak of (100)-oriented samples of 23 arcsec. ZnGa2O4 is a single crystalline spinel phase with the Ga/Zn atomic ratio up to about 2.17. Melt-grown ZnGa2O4 single crystals are thermally stable up to 1100 and 700 °C when subjected to annealing for 10 h in oxidizing and reducing atmospheres, respectively. The obtained ZnGa2O4 single crystals were either electrical insulators or n-type semiconductors/degenerate semiconductors depending on growth conditions and starting material composition. The as-grown semiconducting crystals had the resistivity, free electron concentration, and maximum Hall mobility of 0.002–0.1 Ωcm, 3 × 1018–9 × 1019 cm−3, and 107 cm2 V−1 s−1, respectively. The semiconducting crystals could be switched into the electrically insulating state by annealing in the presence of oxygen at temperatures ≥700 °C for at least several hours. The optical absorption edge is steep and originates at 275 nm, followed by full transparency in the visible and near infrared spectral regions. The optical bandgap gathered from the absorption coefficient is direct with a value of about 4.6 eV, close to that of β-Ga2O3. Additionally, with a lattice constant of a = 8.3336 Å, ZnGa2O4 may serve as a good lattice-matched substrate for magnetic Fe-based spinel films. [ABSTRACT FROM AUTHOR]

Published
2019
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114. Homoepitaxial growth of beta-Ga2O3 layers by metal-organic vapor phase epitaxy

Author

Wagner, Guenter, Baldini, Michele, Gogova, Daniela, Schmidbauer, Martin, Schewski, Robert, Albrecht, Martin, Galazka, Zbigniew, Klimm, Detlef, and Fornari, Roberto

Subjects
Ga2O3, transparent semiconducting oxides, thin films, metal-organic vapor phase epitaxy, structure
Abstract

Epitaxial -Ga2O3 layers have been grown on -Ga2O3 (100) substrates using metal-organic vapor phase epitaxy. Trimethylgallium and pure oxygen or water were used as precursors for gallium and oxygen, respectively. By using pure oxygen as oxidant, we obtained nano-crystals in form of wires or agglomerates although the growth parameters were varied in wide range. With water as an oxidant, smooth homoepitaxial -Ga2O3 layers were obtained under suitable conditions. Based on thermodynamical considerations of the gas phase and published ab initio data on the catalytic action of the (100) surface of -Ga2O3 we discuss the adsorption and incorporation processes that promote epitaxial layer growth. The structural properties of the -Ga2O3 epitaxial layers were characterized by X-ray diffraction pattern and high resolution transmission electron microscopy. As-grown layers exhibited sharp peaks that were assigned to the monocline gallium oxide phase and odd reflections that could be assigned to stacking faults and twin boundaries, also confirmed by TEM. Shifts of the layer peak towards smaller 2 values with respect to the Bragg reflection for the bulk peaks have been observed. After post growth thermal treatment in oxygen-containing atmosphere the reflections of the layers do shift back to the position of the bulk -Ga2O3 peaks, which was attributed to significant reduction of lattice defects in the grown layers after thermal treatment. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Published
2014

117. Scaling-Up of Bulk β-Ga2O3Single Crystals by the Czochralski Method

Author

Galazka, Zbigniew, primary, Uecker, Reinhard, additional, Klimm, Detlef, additional, Irmscher, Klaus, additional, Naumann, Martin, additional, Pietsch, Mike, additional, Kwasniewski, Albert, additional, Bertram, Rainer, additional, Ganschow, Steffen, additional, and Bickermann, Matthias, additional

Published
2016
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121. Low-Cost, Broadly Tunable (375-433 Nm & 746-887 Nm) Cr:Licaf Laser Pumped By One Single-Spatial-Mode Diode

Author

Demirbas, Umit, Uecker, Reinhard, Klimm, Detlef, and Wang, Jing

Abstract

We describe a low-cost, compact, and efficient Cr3+:LiCaAlF6 (Cr:LiCAF) laser that is broadly tunable in the near infrared (746-887 nm) and blue/ultraviolet (375-433 nm) regions of the optical spectrum. The pump source is a 660 nm single-mode-diode with 145 mW of output power. A melt-grown Cr: LiCAF crystal with an extremely high figure of merit above 2000 was used as the gain medium. This enabled the construction of a high-Q-cavity with continuous wave (cw) lasing thresholds as low as 3 mW, slope efficiencies as high as 54%, and output powers up to 63 mW. The stored intracavity power levels were above 30 W. By placing a beta-barium-borate crystal at a second intracavity focus, we could obtain tunable cw blue/ultraviolet radiation with output powers up to 3.5 mW around 400 nm. When mode-locked using a saturable Bragg reflector around 800 nm, the Cr: LiCAF laser produced 95 fs pulses with average powers of 33 mW and peak powers of 3.58 kW at a repetition rate of 85.5 MHz. Extracavity second harmonic generation enables generation of femtosecond pulses around 400 nm. These results demonstrate the possibility to grow Cr: LiCAF crystals with passive losses below 0.15% per cm, which enables construction of low-cost and complexity systems that are pumped only with one low-power single-mode-diode. (c) 2012 Optical Society of America

Published
2012

126. On the bulk β-Ga2O3 single crystals grown by the Czochralski method

Author

Galazka, Zbigniew, primary, Irmscher, Klaus, additional, Uecker, Reinhard, additional, Bertram, Rainer, additional, Pietsch, Mike, additional, Kwasniewski, Albert, additional, Naumann, Martin, additional, Schulz, Tobias, additional, Schewski, Robert, additional, Klimm, Detlef, additional, and Bickermann, Matthias, additional

Published
2014
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128. Solidification of NaCl-LiF- $$\hbox {CaF}_{2}$$ ternary composites.

Author

Acosta, María, Merino, Rosa, Ganschow, Steffen, and Klimm, Detlef

Subjects
SOLIDIFICATION, LITHIUM fluoride, TERNARY alloys, METALLIC composites, METAL microstructure, MELTING
Abstract

The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl-LiF- $$\hbox {CaF}_{2}$$ ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl-LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until $$580\,^{\circ }\hbox {C}$$ is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl-LiF. However, it does not prevent the solidification of homogenous ternary microstructures. [ABSTRACT FROM AUTHOR]

Published
2017
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130. Reevaluation of phase relations in the chemical system neodymium lutetium oxide NdLuO3.

Author

Hirsch, Tamino, Uecker, Reinhard, and Klimm, Detlef

Abstract

The phase relations in the system with the overall chemistry Nd2O3:Lu2O3 around 1:1 were investigated by x-ray diffraction (XRD) of annealed powders and by differential thermal analysis (DTA). A mixture of rare earth oxide solid solutions in the cubic C and in the monoclinic B rare earth oxide structure was determined in the temperature range 1200 to 1650 °C. The C-phase is dominated by Lu content while the B-phase is Nd rich. With rising annealing temperature, the portion of Nd in the C-phase is increased and lowered for the B-phase. Different facilitation possibilities for P-NdLuO3 perovskite formation were discussed and examined but no evidence for stability of this phase could be found experimentally. Two thermal signals of phase transitions were detected. The first occurs at 1908 °C and disappears in second heating run if the temperature is raised too much. Furthermore, a second one was detected at 2121 °C. [ABSTRACT FROM AUTHOR]

Published
2017
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136. Growth, characterization, and properties of bulk SnO2single crystals

Author

Galazka, Zbigniew, primary, Uecker, Reinhard, additional, Klimm, Detlef, additional, Irmscher, Klaus, additional, Pietsch, Mike, additional, Schewski, Robert, additional, Albrecht, Martin, additional, Kwasniewski, Albert, additional, Ganschow, Steffen, additional, Schulz, Detlev, additional, Guguschev, Christo, additional, Bertram, Rainer, additional, Bickermann, Matthias, additional, and Fornari, Roberto, additional

Published
2013
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144. Scaling-Up of Bulk ?-Ga2O3 Single Crystals by the Czochralski Method

Author

Galazka, Zbigniew, Uecker, Reinhard, Klimm, Detlef, Irmscher, Klaus, Naumann, Martin, Pietsch, Mike, Kwasniewski, Albert, Bertram, Rainer, Ganschow, Steffen, and Bickermann, Matthias

Abstract

We present a new approach for scaling-up the growth of b-Ga2O3 single crystals grown from the melt by the Czochralski method, which has also a direct application to other melt-growth techniques involving a noble metal crucible. Experimental and theoretical results point to melt thermodynamics as the crucial factor in increasing the volume of a growing crystal. In particular, the formation of metallic gallium in the liquid phase in large melt volumes causes problems with crystal growth and eutectic or intermetallic phase formation with the noble metal crucible. The larger crystals to be grown the higher oxygen concentration is required. The minimum oxygen concentration ranges from about 8 to 100 vol.% for 2 to 4 inch diameter cylindrical crystals, challenging the use of iridium crucibles in a combination with such high oxygen concentrations. A specific way of oxygen delivery to a growth furnace with the iridium crucible allows to minimize the formation of metallic gallium in the melt and thus obtaining large crystal volumes while decreasing the probability of the eutectic formation.

Published
2017

150. MgGa2O4 as a new wide bandgap transparent semiconducting oxide: growth and properties of bulk single crystals.

Author

Galazka, Zbigniew, Klimm, Detlef, Irmscher, Klaus, Uecker, Reinhard, Pietsch, Mike, Bertram, Rainer, Naumann, Martin, Albrecht, Martin, Kwasniewski, Albert, Schewski, Robert, and Bickermann, Matthias

Subjects
*CRYSTAL gazing, *CRYSTALLINITY, *HYDROGEN, *CRYSTALS, *ELECTRONS
Abstract

Bulk MgGa2O4 single crystals with inverse spinel structure were grown from the melt by different methods. The degree of inversion could be changed by suitable annealing, which was confirmed by differential scanning calorimetry analysis and corresponding changes of the specific heat capacity. MgGa2O4 is thermally much more stable at high temperatures than β-Ga2O3 despite of a higher melting point of about 1930 °C and could be grown under a neutral atmosphere. Melt-grown MgGa2O4 crystals were found to be either electrical insulators or n-type semiconductors depending on the presence of oxygen in the growth atmosphere and the growth method applied. Growing the crystals in the presence of oxygen resulted in electrically insulating crystals. For as-grown and intentionally undoped semiconducting crystals, the free electron concentration was in the range of 1017-1018 cm−3, but the electron mobility was relatively low, just a few cm2V−1s−1. The free electron concentration remained at a level of 1018 cm−3 after annealing in a hydrogen-containing atmosphere at 600-900 °C for 10 h. On the other hand, annealing in an oxygen-containing atmosphere above 600 °C for 10-40 h turns the crystals from the semiconducting to the insulating state. The optical bandgap at room temperature amounts to about 4.9 eV. It decreases with temperature at a rate of 1.35 meV/K. Cathodoluminescence spectra of as-grown crystals show a dominant band at 362 nm. The melt-grown crystals have sufficient size and structural quality to be used as substrates for epitaxy. [ABSTRACT FROM AUTHOR]

Published
2015
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