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Abstract: Nitrides represent an intriguing class of functional materials with a broad range of application fields. Within the past decade, the ammonothermal method became increasingly attractive for the synthesis and crystal growth of nitride materials. The ammonothermal approach proved to be eminently suitable for the growth of bulk III‐nitride semiconductors like GaN, and furthermore provided access to numerous ternary and multinary nitrides and oxonitrides with promising optical and electronic properties. In this minireview, we will shed light on the latest research findings covering the synthesis of nitrides by this method. An overview of synthesis strategies for binary, ternary, and multinary nitrides and oxonitrides, as well as their properties and potential applications will be given. The recent development of autoclave technologies for syntheses at high temperatures and pressures, in situ methods for investigations of crystallization processes, and solubility measurements by ultrasonic velocity experiments is briefly reviewed as well. In conclusion, challenges and future perspectives regarding the synthesis and crystal growth of novel nitrides, as well as the advancement of autoclave techniques are discussed. [ABSTRACT FROM AUTHOR]

The new nitridoalumogermanate Ca1-xLixAl1-x-Ge1+xN3 (x ≈ 0.2) was synthesized from supercritical ammonia at 925 K and 185 MPa starting from the intermetallic precursor Ca3Al2Ge2 and Li as mineralizer. The crystal structure was refined by the Rietveld method; Ca1-xLixAl1-xGe1+xN3 with x ≈ 0.2 [a = 9.9822(5), b = 5.7763(2), c = 5.1484(1) Å, Z = 4, Rwp = 0.0492] crystallizes in orthorhombic space group Cmc21 (no. 36). Needle-shaped crystals with up to 15 μm in length were detected by scanning electron microscopy. Possible cation ordering was analyzed by transmission electron microscopy. No superstructure reflections were observed in electron diffraction patterns and the structure model was confirmed by Z-contrast imaging. The composition was verified by energy-dispersive Xray spectroscopy on single crystals and inductively coupled plasma optical emission spectrometry. Optical properties were studied by diffuse reflectance spectroscopy, showing a broad absorption band between 250 and 300 nm. The optical band gap was estimated to be 4.3 eV at room temperature using the Tauc method. [ABSTRACT FROM AUTHOR]

Abstract: Grimm–Sommerfeld analogous nitrides MgSiN2, MgGeN2, MnSiN2, MnGeN2, LiSi2N3 and LiGe2N3 (generally classified as II‐IV‐N2 and I‐IV2‐N3) are promising semiconductor materials with great potential for application in (opto)electronics or photovoltaics. A new synthetic approach for these nitride materials was developed using supercritical ammonia as both solvent and nitride‐forming agent. Syntheses were conducted in custom‐built high‐pressure autoclaves with alkali metal amides LiNH2, NaNH2 or KNH2 as ammonobasic mineralizers, which accomplish an adequate solubility of the starting materials and promote the formation of reactive intermediate species. The reactions were performed at temperatures between 870 and 1070 K and pressures up to 230 MPa. All studied compounds crystallize in wurtzite‐derived superstructures with orthorhombic space groups Pna21 (II‐IV‐N2) and Cmc21 (I‐IV2‐N3), respectively, which was confirmed by powder X‐ray diffraction. Optical bandgaps were estimated from diffuse reflectance spectra using the Kubelka–Munk function (MgSiN2: 4.8 eV, MgGeN2: 3.2 eV, MnSiN2: 3.5 eV, MnGeN2: 2.5 eV, LiSi2N3: 4.4 eV, LiGe2N3: 3.9 eV). Complementary DFT calculations were carried out to gain insight into the electronic band structures of these materials and to corroborate the optical measurements. [ABSTRACT FROM AUTHOR]

Alkali-alkaline earth metal and alkali-rare earth metal carbodiimides, namely K5-xMx(CN2)2+x(HCN2)1-x (x = 0-1) (M = Sr, Eu) and Na4.32Sr0.68(CN2)2.68(HCN2)0.32, were synthesized under ammonothermal conditions in high-pressure autoclaves. The structures of the three compounds can be derived from homeotypic K5H(CN2)3 and Na5H(CN2)3 by partial substitution of K+ or Na+by Sr2+ or Eu2+. The reactions were carried out in two step syntheses (T1 = 673 K, T2 = 823 K) starting from sodium or potassium azide, dicyandiamide and strontium or Eu(NH2)2, respectively. The crystal structures were solved and refined from single-crystal X-ray diffraction data [K4.16Sr0.84(CN2)2.84(HCN2)0.16: space group Im3m (no. 229), a = 7.8304(5) Å, Z = 2, R1 = 0.024, wR2 = 0.052; K4.40Eu0.60(CN.60(HCN2)0.40: space group Im3m (no.229), a = 7.8304(5) Å, Z = 2, R1 = 0.024, wR2 = 0.052; K4.40Eu0.60(CN2)2.60(HCN2)0.40: space group Im3m (no. 229), a = 7.8502(6) Å, Z = 2, R1 = 0.022, wR2 = 0.049]. In contrast to the potassium carbodiimides, the sodium-strontium carbodiimide was only synthesized as microcrystalline powder. The crystal structure was determined by powder X-ray diffraction and refined by the Rietveld method [Na4.32Sr0.68(CN2)2.68(HCN2)0.32: space group Im3m (no. 229), a = 7.2412(1) Å, Z = 2, wR2 = 0.050]. The presence of hydrogencyanamide units ([HNCN]-) next to carbodiimide units ([CN2]2-) in all compounds was confirmed by FT-IR spectroscopy. [ABSTRACT FROM AUTHOR]

Alkali-alkaline earth metal and alkali-rare earth metal carbodiimides, namely K5-xMx(CN2)2+x(HCN2)1-x (x = 0-1) (M = Sr, Eu) and Na4.32Sr0.68(CN2)2.68(HCN2)0.32, were synthesized under ammonothermal conditions in high-pressure autoclaves. The structures of the three compounds can be derived from homeotypic K5H(CN2)3 and Na5H(CN2)3 by partial substitution of K+ or Na+by Sr2+ or Eu2+. The reactions were carried out in two step syntheses (T1 = 673 K, T2 = 823 K) starting from sodium or potassium azide, dicyandiamide and strontium or Eu(NH2)2, respectively. The crystal structures were solved and refined from single-crystal X-ray diffraction data [K4.16Sr0.84(CN2)2.84(HCN2)0.16: space group Im3m (no. 229), a = 7.8304(5) Å, Z = 2, R1 = 0.024, wR2 = 0.052; K4.40Eu0.60(CN.60(HCN2)0.40: space group Im3m (no.229), a = 7.8304(5) Å, Z = 2, R1 = 0.024, wR2 = 0.052; K4.40Eu0.60(CN2)2.60(HCN2)0.40: space group Im3m (no. 229), a = 7.8502(6) Å, Z = 2, R1 = 0.022, wR2 = 0.049]. In contrast to the potassium carbodiimides, the sodium-strontium carbodiimide was only synthesized as microcrystalline powder. The crystal structure was determined by powder X-ray diffraction and refined by the Rietveld method [Na4.32Sr0.68(CN2)2.68(HCN2)0.32: space group Im3m (no. 229), a = 7.2412(1) Å, Z = 2, wR2 = 0.050]. The presence of hydrogencyanamide units ([HNCN]-) next to carbodiimide units ([CN2]2-) in all compounds was confirmed by FT-IR spectroscopy. [ABSTRACT FROM AUTHOR]

In this contribution, first synthesis of semiconducting ZnSiN2 and ZnGeN2 from solution is reported with supercritical ammonia as solvent and KNH2 as ammonobasic mineralizer. The reactions were conducted in custom-built high-pressure autoclaves made of nickel-based superalloy. The nitrides were characterized by powder X-ray diffraction and their crystal structures were refined by the Rietveld method. ZnSiN2 ( a=5.24637(4), b=6.28025(5), c=5.02228(4) Å, Z=4, Rwp=0.0556) and isotypic ZnGeN2 ( a=5.46677(10), b=6.44640(12), c=5.19080(10) Å, Z=4, Rwp=0.0494) crystallize in the orthorhombic space group Pna21 (no. 33). The morphology and elemental composition of the nitrides were examined by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). Well-defined single crystals with a diameter up to 7 μm were grown by ammonothermal synthesis at temperatures between 870 and 1070 K and pressures up to 230 MPa. Optical properties have been analyzed with diffuse reflectance measurements. The band gaps of ZnSiN2 and ZnGeN2 were determined to be 3.7 and 3.2 eV at room temperature, respectively. In situ X-ray measurements were performed to exemplarily investigate the crystallization mechanism of ZnGeN2. Dissolution in ammonobasic supercritical ammonia between 570 and 670 K was observed which is quite promising for the crystal growth of ternary nitrides under ammonothermal conditions. [ABSTRACT FROM AUTHOR]

We report a detailed investigation of the electronic, mechanical and optical properties of the recently discovered nitridogallosilicate CaGaSiN3 which has potential as a LED-phosphor host material. We focus on chemical disorder effects, originating from the Ga/Si site, and compared them to those of isostructural CaAlSiN3. We calculate the elastic moduli and the Debye temperature in terms of quasi harmonical approximation. Spectral properties like the joint density of states (JDOS) are evaluated and the absorption, reflectance and energy loss function are obtained from the dielectric function. The optical band gap of CaGaSiN3 from experiment is compared to the electronic band gap in terms of electronic DOS and band structure calculations. All properties are evaluated for different ordering models of Ga/Si while the experimentally observed substitutional disorder is accounted for by utilizing the Coherent Potential Approximation (CPA). We conclude a shrinking of the band gap for both CaGaSiN3 and CaAlSiN3 due to atomic disorder, which is unfavorable for potential phosphor applications. This study contributes to materials design considerations, and provides a close look on the electronic impact of substitutional disorder. Moreover, we open the scope for future investigations on solid solutions and phosphor host materials with low doping concentrations. [ABSTRACT FROM AUTHOR]

The first gallium-containing nitridosilicate CaGaSiN3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN3, KN3, and CsN3) on the product formation was investigated as well. The crystal structure of CaGaSiN3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29Si MAS-NMR, and first-principle DFT calculations. CaGaSiN3 crystallizes in the orthorhombic space group Cmc21 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, ( Z=4, Rwp=0.0326), and is isostructural with CaAlSiN3 (CASN). Eu2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN3:Eu2+ also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN3:Eu2+, inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials. [ABSTRACT FROM AUTHOR]

The first gallium-containing nitridosilicate CaGaSiN3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN3, KN3, and CsN3) on the product formation was investigated as well. The crystal structure of CaGaSiN3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29Si MAS-NMR, and first-principle DFT calculations. CaGaSiN3 crystallizes in the orthorhombic space group Cmc21 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, ( Z=4, Rwp=0.0326), and is isostructural with CaAlSiN3 (CASN). Eu2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN3:Eu2+ also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN3:Eu2+, inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials. [ABSTRACT FROM AUTHOR]

Die Umsetzung von Calciumtricyanomethanid mit Fluorwasserstoff führt zur Bildung von Tricyanomethan und Ca(HF2)2. Tricyanomethan ist bis zu einer Temperatur von −40 °C beständig. Es wurde mittels Infrarot ‐ , Raman ‐ und NMR ‐ Spektroskopie charakterisiert. Die Schwingungsspektren sind mit den quantenchemisch berechneten Frequenzen auf PBE1PBE/6 ‐ 311G(3df,3dp) ‐ Niveau verglichen und bestätigen die erwartete C3v ‐ Symmetrie des Moleküls mit regulären C ‐ H ‐ (109.8 pm), C ‐ C ‐ (146.7 pm) und CN ‐ Bindungen (114.7 pm). Nach einer über 100 Jahre andauernden Suche nach Tricyanomethan ist die Synthese des Moleküls nun durch die einfache Reaktion von Calciumtricyanomethanid mit wasserfreiem Fluorwasserstoff bei niedrigen Temperaturen gelungen. [ABSTRACT FROM AUTHOR]

Calcium tricyanomethanide reacts with hydrogen fluoride under formation of tricyanomethane and Ca(HF2)2. Tricyanomethane is stable below −40 °C and was characterized by IR, Raman, and NMR spectroscopy. The vibrational spectra were compared to the quantum-chemical frequencies at the PBE1PBE/6-311G(3df,3dp) level of theory and confirm the predicted C3 v symmetry of the molecule with regular CH (109.8 pm), CC (146.7 pm), and CN (114.7 pm) bonds. [ABSTRACT FROM AUTHOR]

New high‐temperature autoclaves were developed for the ammonothermal synthesis of innovative multinary nitrides. The cover picture shows various in‐house manufactured autoclave components made of a nickel‐based superalloy. Using this equipment the first nitridogallosilicate CaGaSiN3 was synthesized. Eu2+‐doped samples show red luminescence with an emission maximum of 620 nm when irradiated with UV light. Selected area electron diffraction (SAED) patterns on single crystals were recorded, which are represented in the background. More information can be found in the Full Paper by W. Schnick et al. on page 2583 ff. [ABSTRACT FROM AUTHOR]

Grimm-Sommerfeld analogous nitrides MgSiN 2 , MgGeN 2 , MnSiN 2 , MnGeN 2 , LiSi 2 N 3 and LiGe 2 N 3 (generally classified as II-IV-N 2 and I-IV 2 -N 3 ) are promising semiconductor materials with great potential for application in (opto)electronics or photovoltaics. A new synthetic approach for these nitride materials was developed using supercritical ammonia as both solvent and nitride-forming agent. Syntheses were conducted in custom-built high-pressure autoclaves with alkali metal amides LiNH 2 , NaNH 2 or KNH 2 as ammonobasic mineralizers, which accomplish an adequate solubility of the starting materials and promote the formation of reactive intermediate species. The reactions were performed at temperatures between 870 and 1070 K and pressures up to 230 MPa. All studied compounds crystallize in wurtzite-derived superstructures with orthorhombic space groups Pna2 1 (II-IV-N 2 ) and Cmc2 1 (I-IV 2 -N 3 ), respectively, which was confirmed by powder X-ray diffraction. Optical bandgaps were estimated from diffuse reflectance spectra using the Kubelka-Munk function (MgSiN 2 : 4.8 eV, MgGeN 2 : 3.2 eV, MnSiN 2 : 3.5 eV, MnGeN 2 : 2.5 eV, LiSi 2 N 3 : 4.4 eV, LiGe 2 N 3 : 3.9 eV). Complementary DFT calculations were carried out to gain insight into the electronic band structures of these materials and to corroborate the optical measurements., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a detailed investigation of the electronic, mechanical and optical properties of the recently discovered nitridogallosilicate CaGaSiN 3 which has potential as a LED-phosphor host material. We focus on chemical disorder effects, originating from the Ga/Si site, and compared them to those of isostructural CaAlSiN 3 . We calculate the elastic moduli and the Debye temperature in terms of quasi harmonical approximation. Spectral properties like the joint density of states (JDOS) are evaluated and the absorption, reflectance and energy loss function are obtained from the dielectric function. The optical band gap of CaGaSiN 3 from experiment is compared to the electronic band gap in terms of electronic DOS and band structure calculations. All properties are evaluated for different ordering models of Ga/Si while the experimentally observed substitutional disorder is accounted for by utilizing the Coherent Potential Approximation (CPA). We conclude a shrinking of the band gap for both CaGaSiN 3 and CaAlSiN 3 due to atomic disorder, which is unfavorable for potential phosphor applications. This study contributes to materials design considerations, and provides a close look on the electronic impact of substitutional disorder. Moreover, we open the scope for future investigations on solid solutions and phosphor host materials with low doping concentrations.

The first gallium-containing nitridosilicate CaGaSiN 3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN 3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN 3 , KN 3 , and CsN 3 ) on the product formation was investigated as well. The crystal structure of CaGaSiN 3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29 Si MAS-NMR, and first-principle DFT calculations. CaGaSiN 3 crystallizes in the orthorhombic space group Cmc2 1 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, (Z=4, R wp =0.0326), and is isostructural with CaAlSiN 3 (CASN). Eu 2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN 3 :Eu 2+ also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN 3 :Eu 2+ , inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)