The optical absorption edge and near infrared absorption of SrTiO 3 were measured at temperatures from 4 to 1703 K. The absorption edge decreases from 3.25 eV at 4 K to 1.8 eV at 1703 K and is extrapolated to approximately 1.2 eV at the melting point (2350 K). The transmission in the near IR decreases rapidly above 1400 K because of free carrier absorption and is about 50% of the room temperature value at 1673 K. The free carriers are generated by thermal excitation of electrons over the band gap and the formation of charged vacancies. The observed temperature-dependent infrared absorption can be well reproduced by a calculation based on simple models for the intrinsic free carrier concentration and the free carrier absorption coefficient. The measured red shift of the optical absorption edge and the rising free carrier absorption strongly narrow the spectral range of transmission and impede radiative heat transport through the crystal. These effects have to be considered in high temperature applications of SrTiO 3 -based devices, as the number of free carriers rises considerably, and in bulk crystal growth to avoid growth instabilities.Temperature dependent optical absorption edge of SrTiO 3 , measured, fitted, and extrapolated to the melting point.

We report on the identification of a tri-carbon defect in AlN bulk crystals grown by physical vapor transport. The defect gives rise to a single infrared absorption line at 1769 cm−1 in unintentionally carbon doped crystals. This line splits into eight lines in crystals enriched with the carbon isotope 13C. The observed line patterns can unambiguously be assigned to a local vibrational mode of a defect that contains exactly three carbon atoms. The most probable arrangement of the three carbon atoms is on nearest-neighbor substitutional sites, replacing two nitrogen atoms and one aluminum atom, whereby one carbon-carbon bond is directed non-parallel and the other parallel to the crystal's c axis. It is suggested that the tri-carbon defect can exist in three different charge states (neutral, singly negative, and doubly negative) and hence possesses two transition levels within the band gap. This energy level scheme explains the appearance and disappearance of the local vibrational mode in dependence on the Fermi level position as well as a similar appearance-disappearance behavior of a strong ultraviolet absorption band at 4.7 eV that has been repeatedly reported in the literature. We propose that the singly negative charge state of the tri-carbon defect essentially contributes to that ultraviolet absorption.

The pseudobinary system LaLuO 3 -LaScO 3 was explored in hopes of discovering new perovskite-type substrates with pseudocubic lattice parameters above 4 Å. A complete solid solution of the type (LaLuO 3 ) 1-x (LaScO 3 ) x forms between the end members LaLuO 3 and LaScO 3 , enabling large single crystals of (LaLuO 3 ) 1-x (LaScO 3 ) x to be grown from the melt. A single crystal with x≈0.34 was demonstrated. Considering the maximum thermal load of the iridium crucibles appropriate for Czochralski growth of this solid solution, the theoretically maximum achievable x-value is ~0.67. Based on the phase diagram determined, it is anticipated that single crystals with pseudocubic lattice constants between 4.09 and 4.18 Å can be grown in this system by the Czochralski method.

SnO2 is a semiconductor with a wide optical bandgap (3.5 eV), which makes it an attractive transparent semiconducting oxide (TSO) for electronic and opto‐electronic applications. At elevated temperatures it is, however, much more unstable than other TSOs (such as ZnO, Ga2O3, or In2O3). This leads to a rapid decomposition even under very high oxygen pressures. Our experiments showed that stoichiometric SnO2 does not melt up to 2100 °C, in contradiction to earlier published data. Bulk SnO2 single crystals, that could provide substrates for epitaxial growth, have not been reported so far. Hereby we report on truly bulk SnO2 single crystals of 1 inch diameter grown by physical vapor transport (PVT). The most volatile species during SnO2 decomposition is, in addition to oxygen, SnO, which is stable in the gas phase at high temperature and reacts again with oxygen at lower temperatures to form SnO2. We identified a relatively narrow temperature window, temperature gradients and a ratio of SnO/O2 for providing the best conditions for SnO2 single crystal growth. X‐ray powder diffraction (XRD) proved the single SnO2 phase. Moreover, by selecting a suitable SnO/O2 ratio it was possible to obtain either n‐type conductivity with electron concentrations up to 2 × 1018 cm−3 and electron mobilities up to 200 cm2 V−1 s−1, or insulating behavior. The crystals exhibited an optical absorption edge located at 330–355 nm, depending on the crystal orientation, and a good transparency over visible and near infrared (NIR) spectra.

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