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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]

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]

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]

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]

Several metal oxide compounds, especially those containing metals possessing several valence states, are able to absorb or release oxygen under suitable thermodynamic conditions. Such behavior is found often in systems containing oxides of transition metals. It is important to note that the equilibrium oxidation level of those metal oxides can depend on the aggregation state, which may significantly impede crystal growth processes from the melt. If during the melt growth of such oxide crystals, the average valence state of the oxides is different in the molten and solid state, then crystallization is connected with the absorption of free oxygen from the ambient gas, or with the release of free oxygen into it. This phenomenon can be detected by simultaneous DTA/TG measurements and can deteriorate the stability of crystal growth. This holds especially if the average valence in the solid is smaller than in the melt, because oxygen release can lead to bubble formation at the crystallization front. [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]

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]

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]

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]

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]

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]

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]

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]

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: 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]

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]

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]

• 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]

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]

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]

Abstract: Two-inch-diameter γ-LiAlO2 single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the γ-LiAlO2 growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li2O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50mol% Li2O to obtain transparent LiAlO2 crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl5O8 crystallites. [Copyright &y& Elsevier]

• Bulk β-Ga 2 O 3 single crystals are grown the Czochralski method. • The crystals are doped with a number of mono-, di-, tri-, and tetravalent ions. • Incorporation of the dopants into bulk crystals is investigated. • Impact of dopants on growth stability and physical properties of crystals is studied. The present report relates to a systematic study of dopant incorporation into bulk β-Ga 2 O 3 single crystals grown by the Czochralski method, and their impact on growth stability, crystal appearance (growth habit), electrical properties, and transmittance of the obtained crystals. At very similar growth conditions, the dopant incorporation is driven mainly by ionic radii difference between dopant and Ga3+ ion and by thermal stability of the dopant during crystal growth. Good growth stability was achieved with Li1+, Mg2+, Co2+, Ni2+, Ce3+, Al3+, and Ge4+ doping, as that resulted in lowering or entirely compensating the free electron concentration (n e), and, in some cases, presence of additional oxygen through a dopant oxide/carbonate decomposition that is added to the starting material. Undoped crystals had the n e of 2.5 × 1016–2 × 1018 cm−3 with the Hall mobility of 80–152 cm2 V−1 s−1. The n e within that range was also achieved by doping the melt with Li1+, Cu1+, Cr3+, Ce3+, and Ge4+. The two former (Li, Cu) and the latter (Ge) dopants entirely evaporate during or even before growth due to very high partial pressures, but at the same time they leave in the melt extra oxygen that affect to some extent (depending on its initial concentration) the n e. Therefore, we provide a new tool to control the free electron concentration at low levels (n e = 1016–1017 cm−3) by doping a Ga 2 O 3 starting material with thermally unstable oxides or carbonates (such as GeO 2 or Li 2 CO 3) that undergo thermal decomposition at high temperatures with entirely evaporated cations and released in the melt an extra oxygen (dopant acting as an additional oxygen source). Si4+ and Sn4+ increase the n e to 2.5 × 1018–1019 cm−3, consistent with previous studies. At such high n e , the Hall mobility drops to values of 50–84 cm2 V−1 s−1. Divalent ions (Mg2+, Co2+, Ni2+) and trivalent Al3+ made the crystals electrically insulating. We also empirically showed that the underlying conductivity of undoped β-Ga 2 O 3 crystals is caused by residual solid impurities, mainly by Si4+ and hydrogen, the latter could be easily removed by annealing. The transmittance near the absorption edge is not affected by the dopants at studied concentrations, except Cr3+, Co2+, and Ni2+ that introduce an extra absorption in the UV and blue spectral regions, and Al3+ that slightly shifts the absorption edge towards shorter wavelengths. [ABSTRACT FROM AUTHOR]