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The lithium niobate–lithium tantalate solid solution's phase diagram was investigated using experimental data from differential thermal analysis (DTA) and crystal growth. We used XRF analysis to determine the elemental composition of the crystals. The Neumann–Kopp rule provided essential data for the end members lithium niobate (LN) and lithium tantalate (LT). The heats of fusion of the end members, given by DTA measurements, are 103 kJ/mol at 1531 K for LN and 289 kJ/mol at 1913 K for LT. These values were used as input parameters to generate the data. This data served as the basis for calculating a phase diagram for LN-LT solid solutions. Finally, based on the experimental data and a thermodynamic solution model, the Calphad Factsage module optimized the phase diagram. We also generated thermodynamic parameters for Gibbs' excess energy of the solid solution. A plot of the segregation coefficient as a function of Ta concentration was derived from the phase diagram. [ABSTRACT FROM AUTHOR]

The investigation of the structural phase transition in the vicinity of the Curie temperature Tc$T_{\text{c}}$ of LiNb1−xTaxO3$\left(\text{LiNb}\right)_{1 - x} \left(\text{Ta}\right)_{x} \left(\text{O}\right)_{3}$ crystals is motivated by the expected combination of advantageous high‐temperature properties of LiNbO3$\left(\text{LiNbO}\right)_{3}$ and LiTaO3$\left(\text{LiTaO}\right)_{3}$, including high piezoelectric modules and remarkable high‐temperature stability, respectively. Tc$T_{\text{c}}$ marks the ultimate limit for exploiting the piezoelectric properties; however, transition‐related structural modifications might impact this and other properties even below Tc$T_{\text{c}}$. Remarkably, the phase transition from the ferroelectric to the paraelectric phase, whose temperature strongly depends on the composition x, shows a significant drop in the activation energy of the electrical conductivity. The magnitude, temperature dependence, and underlying mechanisms of this drop are discussed from a microscopic perspective. Molecular dynamics calculations in the framework of the density functional theory show that substantial displacements of the cations occur below Tc$T_{\text{c}}$ for both the end compounds LiNbO3$\left(\text{LiNbO}\right)_{3}$ and LiTaO3$\left(\text{LiTaO}\right)_{3}$, and might thus affect the electrical conductivity. Above Tc$T_{\text{c}}$, the migration of lithium ions is presumably facilitated by a shortened diffusion path for the most favorable jump of the lithium ions. Electronic contributions to the conductivity, which become important above 900 K, are explained within the polaronic picture by the formation and migration of free small polarons. [ABSTRACT FROM AUTHOR]

Laser‐flash measurements of the thermal conductivity λ(hkl)$\lambda _{(hkl)}$ of Czochralski‐grown β‐Ga2O3 single crystals are reported perpendicular to four independent crystallographic lattice planes (hkl)=(2¯01)$(hkl)=(\bar{2}01)$, (010), (001), and (100) between room temperature and 1200 K. λ is represented by a symmetric tensor of rank 2 and has four independent components. Tensor components λ11=λ(100)=12.13$\lambda _{11}=\lambda _{(100)}=12.13$ W m−1 K−1 and λ22=λ(010)=24.26$\lambda _{22}=\lambda _{(010)}=24.26$ W m−1 K−1 (values for 300 K) can be directly measured. λ33=14.09$\lambda _{33}=14.09$ W m−1 K−1 and λ13=−0.992$\lambda _{13}=-0.992$ W m−1 K−1, instead, are obtained by combining λ(001)=13.53$\lambda _{(001)}=13.53$ W m−1 K and λ(2¯01)=14.33$\lambda _{(\bar{2}01)}=14.33$ W m−1 K. The crystallographic b⃗$\vec{b}$‐axis is the direction with the highest thermal conductivity, λ22. The thermal conductivity assumes its lowest value (11.73 W m−1 K−1) in a direction close to the crystallographic a⃗$\vec{a}$‐axis. However, this direction does not coincide with a⃗$\vec{a}$, and changes with temperature. [ABSTRACT FROM AUTHOR]

By differential thermal analysis, a concentration field suitable for the growth of Zr, Mg co-doped strontium hexagallate crystals was observed that corresponds well with known experimental results. It was shown that the melting point of doped crystal is ca. 60 K higher than that of undoped crystals. This higher melting points indicate hexagallate phase stabilization by Zr, Mg co-doping and increase the growth window of (Mg,Zr):SrGa12O19, compared to undoped SrGa12O19 that grows from SrO–Ga2O3 melts. [ABSTRACT FROM AUTHOR]

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]

When calcium titanate crystals are grown from stoichiometric melts, they crystallize in the cubic perovskite structure. Upon cooling to room temperature they undergo subsequent phase transitions to tetragonal and orthorhombic modifications. These phase transitions are disruptive and result in severely damaged crystals. This paper presents differential thermal analysis data for several prospective solvents, with the aim to identify a system offering the possibility to perform crystal growth of undistorted CaTiO 3 crystals by crystallizing them significantly below the melting point directly in the low temperature modification. From mixtures CaF 2 :TiO 2 :CaTiO 3  = 3:1:1 (molar ratio) the growth of undistorted, at least millimeter-sized CaTiO 3 crystals is possible. [ABSTRACT FROM AUTHOR]

Simultaneous differential thermal analysis (DTA) and thermogravimetric (TG) measurements with copper oxide/aluminum oxide mixtures were performed in atmospheres with varying oxygen partial pressures and with crucibles made of different materials. Only sapphire and platinum crucibles proved to be stable under conditions that are useful for the growth of CuAlO 2 delafossite single crystals. Then the ternary phase diagram Al 2 O 3 –CuO–Cu and its isopleth section Cu 2 O–Al 2 O 3 were redetermined. Millimeter sized crystals could be obtained from copper oxide melts with 1–2 mol% addition of aluminum oxide that are stable in platinum crucibles held in oxidizing atmosphere containing 15–21% oxygen. [ABSTRACT FROM AUTHOR]

Specific heat capacity measurements by differential scanning calorimetry (DSC) of single crystals of solid solutions of LiNbO3 and LiTaO3 are reported and compared with corresponding ab initio calculations, with the aim to investigate the variation of the ferroelectric Curie temperature as a function of composition. For this purpose, single crystals of these solid solutions were grown with Czochralski pulling along the c-axis. Elemental composition of Nb and Ta was investigated using XRF analysis, and small samples with homogeneous and well known composition were used for the DSC measurements. We observed that the ferroelectric Curie temperature decreases linearly with increasing Ta concentration in the LiNb 1 − x Ta x O3 solid solution crystals. Furthermore, the ferroelectric transition width of a mixed crystal appears to be smaller, as compared to pure LiTaO3. [ABSTRACT FROM AUTHOR]

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]

By differential thermal analysis (DTA) is was shown that the pseudo-binary system Tb 2 O 3 –SiO 2 contains intermediate compounds Tb 2 SiO 5 , Tb 4 Si 3 O 12 and Tb 2 Si 2 O 7. All three compounds melt congruently, a phase diagram was proposed, and from the latter compound single crystals could be grown for the first time. This was possible from stoichiometric feed rods by the optical floating-zone (OFZ) technique. X-ray powder analysis proved the Pna 2 1 phase of the crystals. Melting temperature and heat of fusion were measured by DTA to be 1769◦C and ≈ 150 kJ/mol, respectively. The specific heat capacity of Tb 2 Si 2 O 7 was measured by dynamic DSC to be c p ​= ​149.4982 ​+ ​0.2242 ⋅ T − 7.3913 ​× ​10−5 ⋅ T 2 + 558449.3624 ⋅ T −2. [Display omitted] • Tb 2 O 3 –SiO 2 phase diagram contains three phases – all melt congruently. • Tb 2 Si 2 O 7 single crystal (space group Pna 2 1) grown for the first time. • basic thermal characterization (c p , heat of and temperature of fusion) performed. [ABSTRACT FROM AUTHOR]

The TiO2 rich part of the (1 - x)SrO + xTiO2 phase diagram (0.5 ⩽ x ⩽ 1.0) was redetermined and the eutectic point between SrTiO3 and TiO2 was found at xeut = 0.7700 ± 0.0001; Teut = 1449 ± 3 °C. From TiO2 rich melt solutions, x = 0.75, centimeter-sized single crystals could be grown. The best crystals with an etch pit density of <2 × 104 cm-2 were obtained for growth directions (110) and (100). AFM investigation of the interface reveals layer-by-layer growth. [ABSTRACT FROM AUTHOR]

Abstract: Small ruby crystals were grown by the Czochralski technique in different atmospheres and their actual chromium content was analyzed by a wet chemical method. The chromium distribution coefficient k was found to be strongly dependent on oxygen partial pressure . It ranges from k=0.3 in a reducing atmosphere to k=1.2 in a slightly oxidizing atmosphere and to a good approximation k depends linearly on . The experimental data are discussed on the basis of thermodynamic equilibrium calculations. [Copyright &y& Elsevier]

Abstract: DTA measurements with mixtures of aluminum oxide and lutetium oxide around the perovskite composition were performed up to . A peak with onset was due to the melting of the eutectic (monoclinic phase) and (perovskite). Neither peritectic melting of the perovskite nor its decomposition in the solid phase could be resolved experimentally. The maximum of the eutectic peak size is near , on the Lu-rich side of the perovskite, which is consistent with the conclusion that melts peritectically at ca. as proposed by Wu, Pelton, J. Alloys Compd. 179 (1992) 259. Thermodynamic equilibrium calculation reveals that under strongly reducing conditions (oxygen partial pressure ) aluminum(III) oxide can be reduced to suboxides or even Al metal. It is shown that under such conditions a new phase field with liquid Al can appear. [Copyright &y& Elsevier]

The top‐seeded solution growth for rutile GeO2 single crystals using alkali carbonates or fluorides as flux is applied. Structural data of obtained single crystals confirm the rutile phase with a = b = 4.3966 Å and c = 2.8612 Å. The crystals with diameter of 5–15 mm are either undoped or intentionally doped with Sb5+, Sn4+, Al3+, Ga3+, and F− ions. It is found that Sb5+ is a very efficient n‐type donor enabling free electron concentration even above 1020 cm−3; thus, Sb‐doped GeO2 is a potential substrate for vertical power devices. In contrast, crystals doped with Al and Ga do not show p‐type conductivity suggested by the theory. The onset of the absorption occurs at 5.0 and 5.5 eV perpendicular and parallel to the c‐axis, respectively. Rutile GeO2 shows a very intense photoluminescence peaking at 420 nm (blue) and 520 nm (green). Raman spectra show narrow lines, in particular at high phonon energy (B1g, 170 cm−1). Prepared wafers show FWHM values of rocking curves below 30 arcsec and polishing is achieved down to RMS roughness of 0.15 nm. Transmission electron microscopy images do not show point or extended structural defects with uniform Sb distribution. [ABSTRACT FROM AUTHOR]

Iron(II) oxide, wüstite, is the iron oxide with the lowest oxygen content. Under ambient conditions it is metastable for two reasons: (1) it undergoes eutectoid decomposition to Fe and Fe3O4 below ≈570° C, and (2) depending on temperature, it is thermodynamically stable only for very low oxygen partial pressures, down to below 10−20 bar. Hence, for the growth of single crystals from the melt, the growth atmosphere must contain reducing components to keep the oxygen partial pressure on the required low level. With Ar/CO2/CO mixtures this aim can be reached. It is shown experimentally and by thermodynamic calculation, that the grown crystals contain carbon inclusions. Theoretically it is shown that wüstite crystals without carbon inclusions could be grown in humid N2/H2 mixtures. First experiments are presented in this article, but a further adjustment of experimental parameters is required. [ABSTRACT FROM AUTHOR]

Lithium niobate tantalate (LiNb 1− x Ta x O 3 , LNT) solid solutions offer exciting new possibilities for applications ranging from optics, piezotronics, and electronics beyond the capabilities of the widely used singular compounds of lithium niobate (LiNbO 3 , LN) or lithium tantalate (LiTaO 3 , LT). Crystal growth of homogeneous LNT single crystals by the Czochralski method is still challenging. One key aspect of homogeneous growth is the accurate knowledge of thermal conductivity through the crystal boule during the growth, which is central to control the crystal growth. Therefore, the temperature dependent thermal conductivity of pure LN, LT, and LNT solid solutions, as well as of selected doped LN and LT crystals (Mg, Zn) was investigated across the temperature range from 300 to 1300 K. The results that span across the whole composition range can directly be applied for optimizing growth conditions of both LNT solid solutions as well as doped and undoped LN and LT crystals. [ABSTRACT FROM AUTHOR]

The thermodynamic and crystallographic background for the development of substrate crystals that are suitable for the epitaxial deposition of biaxially strained functional perovskite layers is reviewed. In such strained layers the elastic energy delivers an additional contribution to the Gibbs free energy, which allows the tuning of physical properties and phase transition temperatures to desired values. For some oxide systems metastable phases can even be accessed. Rare‐earth scandates, REScO3, are well suited as substrate crystals because they combine mechanical and chemical stability in the epitaxy process with an adjustable range of pseudo‐cubic lattice parameters in the 3.95 to 4.02 Å range. To further tune the lattice parameters, chemical substitution for the RE or Sc is possible. [ABSTRACT FROM AUTHOR]

We have systematically studied the growth, by the Czochralski method, and basic physical properties of a 2 cm and 2 in. diameter bulk β-(AlxGa1−x)2O3 single crystal with [Al] = 0–35 mol. % in the melt in 5 mol. % steps. The segregation coefficient of Al in the Ga2O3 melt of 1.1–1.2 results in a higher Al content in the crystals than in the melt. The crystals were also co-doped with Si or Mg. [Al] = 30 mol. % in the melt (33–36 mol. % in the crystals) seems to be a limit for obtaining bulk single crystals of high structural quality suitable for homoepitaxy. The crystals were either semiconducting (no intentional co-dopants with [Al] = 0–30 mol. % and Si-doped with [Al] = 15–20 mol. %), degenerately semiconducting (Si-doped with [Al] ≤ 15 mol. %), or semi-insulating ([Al] ≥ 25 mol. % and/or Mg-doped). The full width at half maximum of the rocking curve was 30–50 arcsec. The crystals showed a linear but anisotropic decrease in all lattice constants and a linear increase in the optical bandgap (5.6 eV for [Al] = 30 mol. %). The room temperature electron mobility at similar free electron concentrations gradually decreases with [Al], presumably due to enhanced scattering at phonons as the result of a larger lattice distortion. In Si co-doped crystals, the scattering is enhanced by ionized impurities. Measured electron mobilities and bandgaps enabled to estimate the Baliga figure of merit for electronic devices. [ABSTRACT FROM AUTHOR]

The ternary phase diagram of copper–iron–aluminium delafossite is established with FactSage calculations to improve the conditions for solution growth and the electrical conductivity of the transparent p‐type semiconductor copper–aluminium delafossite by addition of iron oxide. Initial growth experiments with the optical float zone method show that the growth of single crystals with commercially relevant dimensions is not expected in the near future. [ABSTRACT FROM AUTHOR]

Highlights • For the phase diagrams Nb 2 O 5 -Ta 2 O 5 and Nb 2 O 5 -V 2 O 5 a thermodynamic assessment was performed for the first time. • Transformations between different modifications of pure Nb 2 O 5 and Ta 2 O 5 are often kinetically hindered. • The growth of Nb 2 O 5 crystals with size up to ca. 1 cm doped with Ta or V is possible. Abstract The systems Nb 2 O 5 –Ta 2 O 5 and Nb 2 O 5 –V 2 O 5 were investigated using thermal analysis, X-ray powder diffraction and thermodynamic simulations. Solid solution formation is possible for both systems; furthermore, both contain one intermediate compound, VNb 9 O 25 or Ta 2 Nb 4 O 15 , respectively. Phase relationships for pure niobium(V)-oxide and tantalum(V)-oxide were studied under ambient pressure. It was found that both compounds can occur in two stable solid modifications. For niobium(V)-oxide this are the monoclinic high-temperature modification (H-Nb 2 O 5) and an orthorhombic low-temperature modification (T-Nb 2 O 5) and for tantalum(V)-oxide a tetragonal high-temperature form (α -Ta 2 O 5) and an orthorhombic low-temperature form (β -Ta 2 O 5). Based on these results, crystal growth experiments with various compositions from both systems were carried out using the optical floating zone (OFZ) technique. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including point of crystal defects in semiconductors and dielectrics, crystal growth twinning, and the properties and the production of crystalline materials.

Indium oxide as thin film and powder was prepared by the sol-gel method. The structural characterization of the film and powder showed that similar crystallite sizes are obtained in samples heat-treated at the same temperature. Thermo-gravimetric analysis and differential scanning calorimetry were performed in order to determine the activation energies of In 2 O 3 formation from precursors and subsequent crystal growth of both kinds of samples. Absorption measurements showed that the bandgap of the sol-gel polycrystalline films deposited on c-oriented sapphire is in excellent agreement with the one found in bulk and epitaxial indium oxide. The annealed films were found to be highly conductive with carrier concentration generally in excess of 10 19 cm − 3 . It was observed that the electrical characteristics of films annealed at 700 °C remained stable while those of films annealed at lower temperatures exhibited remarkable changes when measurements were repeated after seven months. [ABSTRACT FROM AUTHOR]

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]

Ceramic dielectrics with particularly low levels of dielectric loss and low permittivity are of growing interest toward millimeter‐wave applications. Based on composition and structural considerations, lithic kosmochlor is expected to meet these requirements while exhibiting low densification temperatures, allowing its integration also in co‐fired circuits. Herein, it is found that the spark plasma sintering of LiCrSi2O6 ceramics facilitates densification at temperatures more than 200 °C lower than conventionally processed materials in only a fraction of the time. A spark plasma sintering duration of 10 min is necessary in order to achieve a controllable process with a repeatable high‐performance product material exhibiting a fine‐grained microstructure. Characterization millimeter‐wave frequencies reveal that LiCrSi2O6 materials produced in this manner exhibit excellent dielectric properties (Qf = 80 700 GHz and εr = 7.5 at 134.24 GHz) following densification at only 950 °C with a relative density of 97.4%. These results represent an unprecedented combination of low dielectric losses and processing temperatures for ceramics processed without the addition of sintering aids. The materials and methods explored here present a promising pathway toward high‐performance millimeter‐wave and co‐firable systems. [ABSTRACT FROM AUTHOR]

Small wüstite (Fe 1− x O) crystals were grown using the micro-pulling-down technique. Eutectoid decomposition of the grown crystals was suppressed by fast cooling associated with fast crystal pulling at a rate of 50 mm/min. Crystals grown at lower rates contained magnetite as a second phase indicating the beginning decomposition. Additionally, in those crystals the original wüstite of near-eutectoid composition ( x ≈ 0.05 ) was decomposed into two wüstite phases of which one was iron-poor, x ≈ 0.09 , the other instead iron-rich, near-stoichiometric, x ≈ 0.02 . [ABSTRACT FROM AUTHOR]

Abstract: The eutectic LiF–LiYF4 has been solidified by Bridgman and micro-pulling down (mPD) at pulling rates from 4 to 300mm/h. The microstructure changes from a coupled, interpenetrated-like one to macrofaceted colonies composed of an approximately triangular arrangement of LiF fibers inside the LiYF4 matrix as the pulling rate increases. The cross-over pulling rate is around 3 times larger for the mPD method, corresponding to its larger solidification gradient. The crystallographic growth direction of the matrix phase was found using EBSD. Effective medium estimations of the THz permittivity of the composite predict around the interphase phonon-polariton resonance (wavelength around 17.5μm) a small permittivity hyperbolic behavior specific of the ordered composite that is tolerant to different relative orientations. Water etching of polished cross-sections constitutes a very simple procedure to generate surface micro-holes of predefined size in the LiYF4 matrix. [Copyright &y& Elsevier]

Abstract: We describe continuous-wave (cw) intracavity frequency-doubling experiments performed with a Cr:LiCAF laser. The Cr:LiCAF crystal is home-grown and had passive losses below 0.15% per cm. The laser is pumped by two recently-developed high-brightness tapered diodes, providing a total pump power of 2W at 680nm. The Cr:LiCAF laser generated up to 585mW of cw output power around 800nm with 43% slope efficiency at an absorbed pump power of 1.4W. The low passive losses of the crystal enabled storage of up to 380W of intracavity laser power using a 0.07% transmitting output coupler, demonstrating suitability of Cr:LiCAF gain media for intracavity nonlinear conversion experiments. By performing intracavity frequency doubling with a BBO crystal, cw second-harmonic powers as high as 265mW around 400nm have been realized with optical-to-optical conversion efficiencies as high as 13.3%. To our knowledge, these are the highest cw frequency-doubled laser powers and conversion efficiencies obtained from Cr:Colquiriites to date. Moreover, obtained efficiencies are superior compared to what have been achieved with similar Ti:Sapphire systems, due to lower passive losses of Cr:LiCAF crystal. These results demonstrate the appropriateness of Cr:LiCAF gain media as a high-power tunable cw radiation generator in 375–435nm region. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Two inch diameter, highly conducting (Si-doped) bulk β-Ga2O3 single crystals with the cylinder length up to one inch were grown by the Czochralski method. The obtained crystals revealed high structural quality characterized by narrow x-ray rocking curves (FWHM ≤ 25 arc sec) and high surface smoothness (RMS < 200 pm) of the epi-ready wafers. The free electron concentration and Hall mobility at room temperature were in the range of 1.6–9 × 1018 cm−3 and 118 – 52 cm2 V−1 s−1, respectively, which are not affected by a heat treatment at temperatures up to 1000 °C in an oxidizing atmosphere. Temperature-dependent electrical properties of the crystals revealed a degenerated semiconducting state. Both high structural quality and electrical properties make the crystals well suited as substrates for homoepitaxy and electronic device fabrication in the vertical configuration. [ABSTRACT FROM AUTHOR]

The thermal history of an impact glass from the El'gygytgyn impact structure, central Chukotka, Russia has been investigated with the method of relaxation geospeedometry. The cooling rate of the melt fragment has been quantified by heat capacity ( c p) measurements using differential scanning calorimetry. Cycles of thermal treatments applied to the melt fragment sample result in a set of unique kinetic parameters, which were then used to model heat capacity curves. The Tool-Narayanaswamy-Moynihan approach was used to quantify the natural cooling rate from changes in the normalized heat capacity curves. Cooling rates ranging from 0.06 to 0.40 K min−1 were found by modeling the structural relaxation within the glass transition interval. Because of the absence of thermal reheating, a single natural annealing process is thought to have been responsible for the modeled cooling rate, even though a heat buffering process that affects the cooling history might have been involved. The El'gygytgyn impact glass cooled significantly slower than previously studied tektites and faster than most volcanic glasses. The calculated viscosity of log η = 10.75 ± 0.50 Pa s at the glass transition temperature Tgpeak (1020 K) supports this assumption. Consequently, a slow cooling process is accompanied by a high viscosity η. [ABSTRACT FROM AUTHOR]

Abstract: Solid solutions between zinc oxide and magnesium oxide containing up to 4at.% Mg were grown from the melt using a modified Bridgman technique. Chemical analysis (ICP-OES) and photoluminescence (PL) measurements revealed that the Mg concentration in the melt is larger compared with the starting material. This observation contradicts the commonly accepted assumption, that the ZnO–MgO phase diagram is of eutectic type. Peritectic melting of Zn-rich Zn1−x Mg x O can explain the new experimental results, and a new ZnO–MgO phase diagram is proposed. Furthermore a distribution coefficient for Mg of has been determined. [Copyright &y& Elsevier]

Abstract: The growth of ZnO bulk crystals from the melt is difficult due to the high melting point of the material (T m =1975°C), requiring the use of Ir crucibles, and its thermal decomposition upon heating. A thermodynamic analysis shows that the oxygen partial pressure in the surrounding vapour phase should be as low as possible during the heating cycle at lower temperatures in order to avoid the oxidation of Ir to IrO2. Approaching the ZnO melting point, however, higher oxygen pressure is required for suppressing the ZnO decomposition, while IrO2 decomposes in the elements. The required increasing oxygen supply with increasing temperature can be accomplished by the addition of CO2 to the gas atmosphere. Experimental results prove the correctness of these results. In a Bridgman-like process ZnO boules are obtained that consist of a few large grains with cm dimensions. [Copyright &y& Elsevier]

Abstract: A Bridgman method using induction heating has been developed for growing zinc oxide crystals. Bulk single crystals were prepared in an iridium crucible, where the crucible is directly heated via eddy currents. A high-pressure vessel was used in order to suppress evaporation at the melting point and a carbon dioxide atmosphere is applied to prevent decomposition. Typically, single crystals of 33mm in diameter and 40mm in length have been obtained. The as-grown boules exhibit different transmission properties dependent on the purity of the starting material as well as the cooling rate after crystallization. [Copyright &y& Elsevier]

Abstract: Zinc oxide single crystals were obtained by solidification of a melt contained in an iridium crucible. To the authors knowledge this is the first report on crystal growth of zinc oxide from the melt using an inductively heated metal crucible. This proves that under particular conditions metals are capable of withstanding liquid zinc oxide at high temperatures. Optical microscopy as well as X-ray rocking curve measurements reveal the high crystalline quality of the wafers with full-width at half-maximum values of 22arcsec. Annealing of as-grown samples was observed to have a big influence on optical properties. [Copyright &y& Elsevier]

Pb2Sc2Si2O9 and 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 Pna21 space group and undergo phase transitions to the centrosymmetric Pbcn space group at elevated temperatures. The Pbcn into Pna21 phase 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. [ABSTRACT FROM AUTHOR]

Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation‐dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density‐functional‐theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction. [ABSTRACT FROM AUTHOR]

Cubic rare‐earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large‐size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range. [ABSTRACT FROM AUTHOR]

• Perovskite solid solutions can produce indifferent points with a congruently melting minimum. • Pair selection criteria include a Goldschmidt perovskite tolerance factor close to unity. • Seven solid solution pairs with cubic crystal structure were identified in this study. • These materials have favorable lattice parameters for perovskite substrate applications. • Czochralski/Bridgman growth show that sodium evaporation and attendant hazards are a problem. Single-crystal substrate materials with crystal structures and lattice parameters matching a desired epitaxial film are an enabling technology for many critical materials. Such substrates are best grown by bulk techniques that benefit from the substrate material being congruently melting. The shortage of congruently melting perovskites in critical lattice parameter ranges has been addressed herein by a search for new congruently melting compositions. A solid solution of two perovskites can be congruently melting at a minimum temperature under specified thermodynamic conditions where the coefficient matrix has a zero determinant. This is called an indifferent point. A wide variety of perovskite solid solutions were investigated to identify compounds that have an indifferent melting minimum and a cubic crystal structure with favorable lattice constants in the range of 0.390–0.412 nm. Solid solution pairs that form such indifferent points include, but are not limited to, seven compositions identified in this study. The lattice parameters of the new materials show a broad range of desirable lattice constants. A perovskite tolerance factor close to unity gave a favorable contribution to the free energy and makes a cubic crystal structure favorable. These solid solutions constitute a broad and important class of compounds not previously anticipated. The only significant drawback is the high vapor pressure of sodium, which is present in most of these materials and requires special growth conditions and equipment for safety. [ABSTRACT FROM AUTHOR]

• CFD model with thermodynamic calculations is proposed for Cz-β-Ga 2 O 3 growth. • Impact of SO 2 and CO 2 on the Ga 2 O 3 stoichiometric ratio deviations is simulated. • The benefits of using SO 2 over CO 2 for the Cz-growth of β-Ga 2 O 3 are showcased. • Effect of the melt-free surface area on the melt stoichiometry is illustrated. • The ideal melt stoichiometry is achieved at ca. 40% SO 2 and 9% CO 2. The present study focuses on computer modeling of Cz- β-Ga 2 O 3 crystal growth while also addressing the issue of minimizing Ir crucible oxidation. To accomplish this objective, a comprehensive framework was developed that combines thermodynamic equilibrium calculations with a CFD numerical model. This integrated approach is designed to simulate the impact of SO 2 gas concentration in the chamber atmosphere. The primary goal of this numerical model is to assess deviations from the stoichiometric ratio in the Ga 2 O 3 melt by examining the processes taking place at the free surface of the melt and their effects on its stoichiometry. These processes include the dissociation of the Ga 2 O 3 melt into Ga and O ions, as well as the evaporation of volatile species from the melt surface. Simulations were conducted for both 2-inch and 4-inch crystals, with varying concentrations of SO 2 and CO 2 in an Ar atmosphere, facilitating a direct comparison between the two gases. The study's findings indicate that the optimal concentration of SO 2 in the atmosphere should be approximately 40%, whereas for CO 2 , the optimal concentration is around 9%. Significantly reduced concentrations of both SO 2 and CO 2 were achieved by increasing the free melt surface area. Notably, the atmosphere with a SO 2 concentration exhibited a substantial 30% reduction in the O concentration surrounding the crucible, underlining the advantages of using SO 2 as a viable alternative to CO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium carbonate in its various polymorphs reacts with sodium silicate solution. • This reaction results in formation of Na-containing C-S-H and sodium carbonates. • Formation of natron and C-S-H are observed at time of second calorimetric peak. • Formation of natron or thermonatrite depends upon the kinetics of reaction. • With higher reaction degree of calcite, formation of gaylussite is predicted. This article investigates the role of calcium carbonate minerals in an alkali-activated system through their reaction with sodium silicate solution. The early reaction kinetics and reaction products are investigated using isothermal conduction calorimetry, in-situ XRD and in-situ FTIR. Later reaction products are identified with thermodynamic modelling and analysis of the paste samples after 8 and 90 d using XRD, TGA, DSC and mass spectrometry. After a few hours of reaction, natron precipitates as the first crystalline carbonate phase, while changes in the connectivity of silicates are observed due to the precipitation of C-S-H, which may contain Na. After 8 and 90 d, C-S-H is observed together with thermonatrite instead of natron. It is shown that calcium carbonate is not just a filler in an alkali-activated system but can provide Ca to form C-S-H and can also enhance the availability of carbonate for the formation of alkali carbonates. [ABSTRACT FROM AUTHOR]

Highlights • Crystal growth between NdLuO 3 and NdScO 3 from the melt is performed. • From NdScO 3 rich melts perovskite type crystals are obtained. • Perovskite phase in the subsolidus is stable for almost arbitrary composition. • Liquidus projection of the Nd 2 O 3 –Lu 2 O 3 –Sc 2 O 3 ternary is presented. Abstract Based on differential thermal analysis (DTA) and X-ray powder diffraction (XRD), a description of the Nd 2 O 3 –Lu 2 O 3 –Sc 2 O 3 system was obtained by thermodynamic assessment. Four fields of primary crystallization could be identified; from melt compositions close to the Lu 2 O 3 –Sc 2 O 3 edge, the rare-earth oxide C-phase crystallizes first which is stable down to room temperature. From Nd 2 O 3 rich melts, the X-phase forms which is stable only at high temperatures. An additional field, where the alternative high-temperature phase H solidifies as primary product touches the Nd 2 O 3 –Lu 2 O 3 edge of the concentration triangle. From melts close to the composition NdScO 3 , the P-phase (perovskite) can be crystallized and mixed crystals with second endmember NdLuO 3 have been grown from the melt. Crystals of this mixed perovskite were grown by the micro-pulling-down and Czochralski methods. [ABSTRACT FROM AUTHOR]

Highlights • Growth of Al 1−x Sc x N bulk single crystals. • Substrate for AlGaN based UVB optoelectronic devices. • Sublimation by physical vapor transport (PVT). • Aluminum scandium nitride alloy growth. Abstract We describe the preparation of wurtzite Al 1−x Sc x N bulk single crystals by physical vapor transport by introducing scandium to the aluminum nitride (AlN) source material. The Al 1−x Sc x N single crystals obtained exhibit a maximum scandium atomic concentration of about x = 0.55% in axial c-direction while being uniform within the c-plane. The high structural quality as determined by high resolution x-ray diffraction is comparable to that of AlN bulk crystals. However, the incorporated scandium concentration is about 15 times lower than expected from thermodynamic considerations. This behavior is ascribed to a pronounced scandium segregation or agglomeration in the gas phase and parasitic deposition/loss of ScN during growth. [ABSTRACT FROM AUTHOR]

The reduction of SiC, Si 3 N 4 and transition metals impurities in directionally solidified Si ingots poses one of the crucial challenges in the solar cells production. Particularly strong contamination comes from the graphite parts in the hot zone. Therefore, we selected three massive ceramic materials to replace graphite, developed the novel design of the crucible support and cover and compared the crystals grown in them with ingots from the standard graphite design. The experiments were performed for phosphorus n-doped silicon of G0 size. The ingots were compared with respect to O- and C-content, metal impurities, resistivity and lifetime. The superior performance of TiC relative to other ceramics was observed, particularly due to the lower concentration of substitutional carbon in Si ingot (up to 2.6 times) and the higher minority carrier lifetime of (up to 4.4 times) with narrow red zones. [ABSTRACT FROM AUTHOR]

High-temperature thermal properties of three neighboring rare-earth scandates DyScO 3 , TbScO 3 and GdScO 3 were compared to La 0.29 Sr 0.71 Al 0.65 Ta 0.35 O 3 (LSAT) and sapphire. To calculate thermal conductivity, heat capacity and thermal diffusivity were measured by differential scanning calorimetry and laser flash technique, respectively. DyScO 3 and TbScO 3 showed an untypical rise in the thermal conductivity above 900 K, while for GdScO 3 , LSAT and sapphire the expected decrease at elevated temperatures could be observed. [ABSTRACT FROM AUTHOR]

We experimentally evaluated segregation of Cr, Ce and Al in bulk β-Ga 2 O 3 single crystals grown by the Czochralski method, as well as the impact of these dopants on optical properties. The segregation of Cr and Ce and their incorporation into the β-Ga 2 O 3 crystal structure strongly depends on O 2 concentration in the growth atmosphere which has a noticeable impact on decomposition of Ga 2 O 3 and Cr 2 O 3 , as well as on the charge state of Cr and Ce. Effective segregation coefficients for Cr are in the range of 3.1–1.5 at 7–24 vol% O 2 , while for Ce they are roughly below 0.01 at 1.5–34 vol% O 2 . The effective segregation coefficient for Al is 1.1 at 1.5–21 vol% O 2 . Both dopants Ce and Al have a thermodynamically stabilizing effect on β-Ga 2 O 3 crystal growth by supressing decomposition. While Ce has no impact on the optical transmittance in the ultraviolet and visible regions, in Cr doped crystals we observe three absorption bands due to Cr 3+ on octahedral Ga sites, one in the ultraviolet merging with the band edge absorption of β-Ga 2 O 3 and two in the visible spectrum, for which we estimate the absorption cross sections. Al doping also does not induce dopant related absorption bands but clearly shifts the absorption edge as one expects for a solid-solution crystal Ga 2(1−x) Al 2x O 3 still in the monoclinic phase. For the highest doping concentration (Ga 1.9 Al 0.1 O 3 ) we estimate an increase of the energy gap by 0.11 eV. [ABSTRACT FROM AUTHOR]

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]

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. [ABSTRACT FROM AUTHOR]

Sn-doped β-GaO epitaxial layers have been grown on (100) β-GaO substrates by metal organic vapour-phase epitaxy. Triethylgallium (TEGa), molecular oxygen (O) and tetraethyltin (TESn) were used as Ga, O and Sn precursors, respectively. Layers grown at optimized temperature and chamber pressure, i.e. 850 °C and 5 mbar, had flat surfaces with a rms roughness of about 600 pm. Structural analysis by transmission electron microscopy revealed that the main defects in the layers were stacking faults and twin lamella. The incoherent boundaries of these defects are supposed to act as compensation and scattering centres, limiting the carrier mobility. Sn was homogeneously incorporated with a flat profile throughout the whole layer at concentration levels ranging from 2 × 10 to 3 × 10 cm proportionally to the used TESn flux. All layers were electrically conductive. However, an unambiguous Hall effect was measurable only for Sn concentrations higher than 1 × 10 cm, resulting in electron concentrations from 5 × 10 to 2 × 10 cm at room temperature. For increasing free carrier concentrations, the electron mobility showed the tendency to increase from 10 to 30 cm/Vs. The maximum mobility of 41 cm/Vs, measured in a sample with free carrier concentration of 1 × 10 cm, represents the highest value reported for β-GaO layers grown by MOVPE so far. [ABSTRACT FROM AUTHOR]

Measurements of thermal diffusivity ? (using laser flash analysis) for temperatures from 100 °C to 1200 °C and of the inversion parameter x (using X-ray analysis) for the single crystal spinel MgGa2O4 have been performed. X-ray analysis showed a small change in x for samples annealed at 800 °C (x = 0.838) and 1200 °C (x = 0.834). Thermal diffusivity revealed a significant rise of ? for temperatures higher than 950 °C, deviating from the typical 1/T drop of ?. An additional systematic rise of ? with time is observed for temperatures between 950 °C and 1100 °C. A connection between cation disordering processes typical for spinels at elevated temperatures and the observed deviation of ? is proposed: Data indicate that cations changing their occupancy site at equilibration processes contribute significantly to ? and therefore represent a new type of heat transport. [ABSTRACT FROM AUTHOR]

Cylindrical SrTiO3 single crystals with diameters and lengths exceeding one inch were grown from non-stoichiometric melts below 1800 °C using the high temperature top-seeded solution growth (TSSG) method. Despite the large crystal diameter the quality has been improved compared to Verneuil grown crystals. Typical etch pit density (EPD) values are in the range between 2 × 104 and 2 × 105 cm−2 for bulk crystals pulled in the ＜100＞ direction and using seeds with EPD values of 5 × 105 cm−2. So far pulling SrTiO3 crystals from the melt suffers from growth instabilities like foot formation and subsequent spiraling. To avoid them an effective heat transport via the crystal is indispensable. Especially at elevated temperatures it requires a high optical transparency in the infrared region. In this paper we report the correlation between oxygen partial pressure, composition, IR-transmittance and coloration of the crystals. The growth at a sufficiently high oxygen partial pressure leads to an increase in the optical transparency of the crystals and can thereby suppress foot or spiral formation. [ABSTRACT FROM AUTHOR]