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The research for wurtzite-type ternary nitride semiconductors containing earth abundant elements with a stoichiometry of 1:1:2 was focused on metals like Mg or Zn, so far. The vast majority of these Grimm-Sommerfeld analogous compounds crystallize in the ß-NaFeO2 structure, although a second arrangement in space group Pmc21 is predicted to be a viable alternative. Despite extensive theoretical and experimental studies, this structure has so far remained undiscovered. Herein, we report on BeGeN2 in a Pmc21 structure, synthesized from Be3N2 and Ge3N4 using a high-pressure high-temperature approach at 6 GPa and 800 °C. The compound was characterized by powder X-ray diffraction (PXRD), solid state nuclear magnetic resonance (NMR), Raman and energy dispersive X-ray (EDX) spectroscopy, temperature-dependent PXRD, second harmonic generation (SHG) and UV/VIS measurements and in addition also compared to its lighter homologue BeSiN2 in all mentioned analytic techniques. The synthesis and investigation of both the first beryllium germanium nitride and the first ternary wurtzite-type nitride crystallizing in space group Pmc21 open the door to a new field of research on wurtzite-type related structures.
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Nitridophosphates are in the focus of current research interest due to their structural versatility and properties, such as ion conductivity, ultra-incompressibility and luminescent properties when doped with suitable activator ions. Multinary representatives often require thorough investigation due to the competition with the thermodynamically more stable binary and ternary compounds. Another point of concern is the synthetic control of structural details, which is usually limited by conventional bottom-up syntheses. In this study, we report on the synthesis and characterization of the quaternary nitridophosphate CaLi2PN3. Various synthesis protocols were used for the preparation of CaLi2PN3, including the novel nitridophosphate double salt approach. The crystal structure was solved and refined from single-crystal X-ray diffraction data and confirmed by Rietveld refinement, solid-state NMR spectroscopy, EDX measurements and low-cost crystallographic calculations. The experimental results were corroborated by DFT calculations, which revealed the electronic band structure. Formation energy calculations allowed conclusions to be drawn about the stability in comparison to the initial ternary nitridophosphates. The synthesis of CaLi2PN3 exemplifies the enormous potential of medium-pressure syntheses in the field of nitridophosphate research. Furthermore, the presented new synthesis route allows a certain degree of structural control, which is a promising addition to previous synthesis strategies in nitridophosphate chemistry.
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We report on the synthesis, crystal, and electronic structure, as well as the magnetic, and electric properties of the phosphorus-containing tantalum nitride P1-xTa8+xN13 (x = 0.1-0.15). A high-pressure high-temperature reaction (8 GPa, 1400 °C) of Ta3N5 and P3N5 with NH4F as a mineralizing agent yields the compound in the form of black, rod-shaped crystals. Single-crystal X-ray structure elucidation (space group C2/m (no. 12), a = 16.202(3), b = 2.9155(4), c = 11.089(2) Å, ß = 126.698(7)°, Z = 2) shows a network of face- and edge-sharing Ta-centered polyhedra that contains small vacant channels and PN6 octahedra strands. Atomic resolution transmission electron microscopy reveals an unusual P/Ta disorder. Mixed-valent tantalum atoms exhibit interatomic distances similar to those in metallic tantalum, however, the electrical resistivity is quite high in the order of 101 Ω cm. The density of states and the electron localization function indicate localized electrons in both covalent and ionic bonds between P/Ta and N atoms, combined with less localized electrons that do not contribute to interatomic bonds.
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Ammeline is a simple, readily available, molecular compound, which has been known for nearly 200â years. Despite that, no proper structural characterization of ammeline has been conducted so far. For this reason, the prevalent tautomeric form of ammeline in the solid remained unknown to this date. In the course of this study, its crystal structure was finally established by single-crystal X-ray diffraction. In this structure, ammeline is exclusively found as its 4,6-diamino-1,3,5-triazin-2(1H)-one tautomer and adopts layered structure with an exceptionally high hydrogen bond density. Ammeline shows an interesting amphoteric behavior. Therefore, the synthesis and structural characterization of some of its salts were carried out to investigate the influence of the protonation degree on its molecular structure. In particular, the crystal structure of silver ammelinate monohydrate was solved as the first reported structure containing deprotonated ammeline. Moreover, the crystal structures of three different modifications of ammelinium perchlorate were elucidated and the transformation conditions between them were studied. Lastly, the crystal structure of ammelinediium diperchlorate monohydrate, containing unprecedented doubly protonated ammeline, was determined. The products' thermal behavior was studied by differential thermal analysis and thermogravimetric analysis. The perchlorate salts were additionally examined for their potential as insensitive high-energy-density materials.
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Nitridophosphates, with their primary structural motif of isolated or condensed PN4 tetrahedra, meet many requirements for high performance materials. Their properties are associated with their structural diversity, which is mainly limited by this specific building block. Herein, we present the alkaline earth metal nitridophosphate oxide Ba3[PN3]O featuring a trigonal planar [PN3]4- anion. Ba3[PN3]O was obtained using a hot isostatic press by medium-pressure high-temperature synthesis (MP/HT) at 200â MPa and 880 °C. The crystal structure was solved and refined from single-crystal X-ray diffraction data in space group R 3 â¾ ${\bar 3}$ c (no. 167) and confirmed by SEM-EDX, magic angle spinning (MAS) NMR, vibrational spectroscopy (Raman, IR) and low-cost crystallographic calculations (LCC). MP/HT synthesis reveals great potential by extending the structural chemistry of P to include trigonal planar [PN3]4- motifs.
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Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high-pressure high-temperature reaction at 800 °C and 6â GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single-crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, ß=109.624(1)°) and shows a 3D-network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight-membered rings of vertex-sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid-state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature-dependent powder X-ray diffraction measurements reveal a low thermal expansion of 3.6â ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose.
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The imidonitridosilicate Rb3Si6N5(NH)6, being only the second representative of this compound class, was synthesized ammonothermally at 870â K and 230â MPa. Its crystal structure was solved from single-crystal X-ray diffraction data. The imidonitridosilicate crystallizes isotypically with the respective potassium compound in space group P4132 with the lattice parameter a=10.9422(4)â Å forming a three-dimensional imidonitridosilicate tetrahedra network with voids for the rubidium ions. The structure model and the presence of the imide groups were verified by Fourier-Transform infrared (FTIR) and magic-angle spinning (MAS) NMR spectroscopy, using cross polarization 15N{1H} and 29Si{1H} MAS NMR experiments. Rb3Si6N5(NH)6 represents a possible intermediate during the ammonothermal synthesis of nitridosilicates. The characterization of such intermediates improves the understanding of the reaction pathway from ammonothermal solutions to nitrides. Thus, the ammonothermal synthesis is an alternative approach to the well-established high-temperature synthesis leading to the compound class of nitridosilicates.
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Although beryllium and its compounds show outstanding properties, owing to its toxic potential and extreme reaction conditions the chemistry of Be under high-pressure conditions has only been investigated sparsely. Herein, we report on the highly condensed wurtzite-type Be2PN3, which was synthesized from Be3N2 and P3N5 in a high-pressure high-temperature approach at 9â GPa and 1500 °C. It is the missing member in the row of formula type M2PN3 (M = Mg, Zn). The structure was elucidated by powder X-ray diffraction (PXRD), revealing that Be2PN3 is a double nitride, rather than a nitridophosphate. The structural model was further corroborated by 9Be and 31P solid-state nuclear magnetic resonance (NMR) spectroscopy. We present 9Be NMR data for tetrahedral nitride coordination for the first time. Infrared and energy-dispersive X-ray spectroscopy (FTIR and EDX), as well as temperature dependent PXRD complement the analytical characterization. Density functional theory (DFT) calculations reveal super-incompressible behavior and the remarkable hardness of this low-density material. The formation of Be2PN3 through a high-pressure high-temperature approach expands the synthetic access to Be-containing compounds and may open access to various multinary beryllium nitrides.
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Tetrahedron-based nitrides offer a wide range of properties and applications. Highly condensed nitridophosphates are examples of nitrides that exhibit fascinating luminescence properties when doped with Eu2+, making them appealing for industrial applications. Here, we present the first nitridomagnesophosphate solid solution series Ba3-xSrx[Mg2P10N20] : Eu2+ (x=0-3), synthesized by a high-pressure high-temperature approach using the multianvil technique (3â GPa, 1400 °C). Starting from the binary nitrides P3N5 and Mg3N2 and the respective alkaline earth azides, we incorporate Mg into the P/N framework to increase the degree of condensation κ to 0.6, the highest observed value for alkaline earth nitridophosphates. The crystal structure was elucidated by single-crystal X-ray diffraction, powder X-ray diffraction, energy-dispersive X-ray spectroscopy (EDX), and solid-state NMR. DFT calculations were performed on the title compounds and other related highly condensed nitridophosphates to investigate the influence of Mg in the P/N network. Eu2+-doped samples of the solid solution series show a tunable narrow-band emission from cyan to green (492-515â nm), which is attributed to the preferred doping of a single crystallographic site. Experimental confirmation of this assumption was provided by overdoping experiments and STEM-HAADF studies on the series as well on the stoichiometric compound Ba2Eu[Mg2P10N20] with additional atomic resolution energy-dispersive X-ray spectroscopy (EDX) mapping.
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Nitridophosphates and nitridogermanates attract high interest in current research due to their structural versatility. Herein, the elastic properties of GeP2N4 were investigated by single-crystal X-ray diffraction (XRD) upon compression to 44.4(1) GPa in a diamond anvil cell. Its isothermal bulk modulus was determined to be 82(6) GPa. At 44.4(1) GPa, laser heating resulted in the formation of multiple crystalline phases, one of which was identified as unprecedented germanium nitridophosphate GePN3. Its structure was elucidated from single-crystal XRD data (C2/c (no. 15), a = 8.666(5), b = 8.076(4), c = 4.691(2) Å, ß = 101.00(7)°) and is built up from layers of GeN6 octahedra and PN4 tetrahedra. The GeN6 octahedra form double zigzag chains, while the PN4 tetrahedra are found in single zigzag chains. GePN3 can be recovered to ambient conditions with a unit cell volume increase of about 12%. It combines PV and GeIV in a condensed nitridic network for the first time.
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We report on the synthesis of two-layered alkali germanates, Na2Ge4O7 and K2Ge4O7. Both compounds were synthesized by using the ammonothermal method at 823 K and 100 MPa. Under these conditions, germanium is partially reduced from the +IV state to +II, forming mixed-valence compounds with the rarely observed [Ge(II)O3]4- unit. The valence state was verified by X-ray photoelectron spectroscopy (XPS) and was accompanied by theoretical calculations alongside vibrational spectroscopy and single-crystal X-ray structure determination. The compounds crystallize in the trigonal space groups (Na2Ge4O7: P3Ì c1 and K2Ge4O7: P3Ì m1) and feature layers of corner sharing [Ge(II)O3]4- and [Ge(IV)2O7]6- units forming [Ge(II)2Ge(IV)2O7]2- polyanions. These layers are separated by alkali metal ions. The compounds are colorless insulators with band gaps of 4.0-4.2 eV. According to the Robin-Day classification, both compounds can be described as class I materials, where the valences are trapped on specific sites.
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A series of isostructural imidonitridophosphates AE2AlP8N15(NH) (AE=Ca, Sr, Ba) was synthesized at high-pressure/high-temperature conditions (1400 °C and 5-9 GPa) from alkaline-earth metal nitrides or azides Ca3N2/Sr(N3)2/Ba(N3)2 and the binary nitrides AlN and P3N5. NH4F served as a hydrogen source and mineralizing agent. The crystal structures were determined by single-crystal X-ray diffraction and feature a three-dimensional network of vertex-sharing PN4-tetrahedra forming diverse-sized rings that are occupied by aluminum and alkaline earth ions. These structures represent another example of nitridophosphate-based networks that simultaneously incorporate AlN6-octahedra and alkaline-earth-centered polyhedra, with aluminum not participating in the tetrahedra network. They differ from previously reported ones by incorporating non-condensed octahedra instead of strongly condensed octahedra units and contribute to the diversity of multicationic nitridophosphate network structures. The results are supported by atomic resolution EDX mapping, solid-state NMR and FTIR measurements. Eu2+-doped samples show strong luminescence with narrow emissions in the range of green to blue under UV excitation, marking another instance of Eu2+-luminescence within imidonitridophosphates.
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We have previously presented a computational protocol that is based on an embedded cluster model and operates in the framework of TD-DFT in conjunction with the excited state dynamics (ESD) approach. The protocol is able to predict the experimental absorption and emission spectral shapes of Eu2+-doped phosphors. In this work, the applicability domain of the above protocol is expanded to Eu2+-doped phosphors bearing multiple candidate Eu doping centers. It will be demonstrated that this protocol provides full control of the parameter space that describes the emission process. The stability of Eu doping at various centers is explored through local energy decomposition (LED) analysis of DLPNO-CCSD(T) energies. This enables further development of the understanding of the electronic structure of the targeted phosphors, the diverse interactions between Eu and the local environment, and their impact on Eu doping probability, and control of the emission properties. Hence, it can be employed to systematically improve deficiencies of existing phosphor materials, defined by the presence of various intensity emission bands at undesired frequencies, towards classes of candidate Eu2+-doped phosphors with desired narrow band red emission. For this purpose, the chosen study set consists of three UCr4C4-based narrow-band phosphors, namely the known alkali lithosilicates RbNa[Li3SiO4]2:Eu2+ (RNLSO2), RbNa3[Li3SiO4]4:Eu2+ (RNLSO) and their isotypic nitridolithoaluminate phosphors consisting of CaBa[LiAl3N4]2:Eu2+ (CBLA2) and the proposed Ca3Ba[LiAl3N4]4:Eu2+ (CBLA), respectively. The theoretical analysis presented in this work led us to propose a modification of the CBLA2 phosphor that should have improved and unprecedented narrow band red emission properties. Finally, we believe that the analysis presented here is important for the future rational design of novel Eu2+-doped phosphor materials, with a wide range of applications in science and technology.
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The first nitridic analog of an amphibole mineral, the quaternary nitridosilicate phosphate Cr5.7Si2.3P8N24 was synthesized under high-pressure high-temperature conditions at 1400 °C and 12â GPa from the binary nitrides Cr2N, Si3N4 and P3N5, using NH4N3 and NH4F as additional nitrogen source and mineralizing agent, respectively. The crystal structure was elucidated by single-crystal X-ray diffraction with microfocused synchrotron radiation (C2/m, a=9.6002(19), b=17.107(3), c=4.8530(10)â Å, ß=109.65(3)°). The elemental composition was analyzed by energy dispersive X-ray spectroscopy. The structure consists of vertex-sharing PN4-tetrahedra forming zweier double chains and edge-sharing (Si,Cr)-centered octahedra forming separated ribbons. Atomic resolution scanning transmission electron microscopy shows ordered Si and Cr sites next to a disordered Si/Cr site. Optical spectroscopy indicates a band gap of 2.1â eV. Susceptibility measurements show paramagnetic behavior and support the oxidation state Cr+IV, which is confirmed by EPR. The comprehensive analysis expands the field of Cr-N chemistry and provides access to a nitride analog of one of the most prevalent silicate structures.
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High-pressure, high-temperature (HP/HT) syntheses are essential for modern high-performance materials. Phosphorus nitride, nitridophosphate, and more generally nitride syntheses benefit greatly from HP/HT conditions. In this contribution, we present the first systematic in situ investigation of a nitridophosphate HP/HT synthesis using the reaction of zinc nitride Zn3N2 and phosphorus(V) nitride P3N5 to the nitride semiconductor Zn2PN3 as a case study. At a pressure of 8 GPa and temperatures up to 1300 °C, the reaction was monitored by energy-dispersive powder X-ray diffraction (ED-PXRD) in a large-volume press at beamline P61B at DESY. The experiments investigate the general behavior of the starting materials under extreme conditions and give insight into the reaction. During cold compression and subsequent heating, the starting materials remain crystalline above their ambient-pressure decomposition points, until a sufficient minimum temperature is reached and the reaction starts. The reaction proceeds via ion diffusion at grain boundaries with an exponential decay in the reaction rate. Raising the temperature above the minimum required value quickly completes the reaction and initiates single-crystal growth. After cooling and decompression, which did not influence the resulting product, the recovered sample was analyzed by energy-dispersive X-ray (EDX) spectroscopy.
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This study presents the synthesis and characterization of oxonitridosilicate phosphates Sr3SiP3O2N7, Sr5Si2P4ON12, and Sr16Si9P9O7N33 as the first of their kind. These compounds were synthesized under high-temperature (1400 °C) and high-pressure (3â GPa) conditions. A unique structural feature is their common fundamental building unit, a vierer single chain of (Si, P)(O, N)4 tetrahedra. All tetrahedra comprise substitutional disorder which is why we refer to it as the fundamental disorder unit (FDU). We classified four different FDU motifs, revealing systematic bonding patterns. Including literature known Sr5Si2P6N16, three of the four patterns were found in the presented compounds. Common techniques like single-crystal X-ray diffraction (SCXRD), elemental analyses, and 31P nuclear magnetic resonance (NMR) spectroscopy were utilized for structural analysis. Additionally, low-cost crystallographic calculations (LCC) provided insights into the structure of Sr16Si9P9O7N33 where NMR data were unavailable due to the lack of bulk samples. The optical properties of these compounds, when doped with Eu2+, were investigated using photoluminescence excitation (PLE), photoluminescence (PL) measurements, and density functional theory (DFT) calculations. Factors influencing the emission properties, including thermal quenching mechanisms, were discussed. This research reveals the new class of oxonitridosilicate phosphates with unique systematic structural features that offer potential for theoretical studies of luminescence and band gap tuning in insulators.
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Alkali nitridophosphates AP4 N7 and A3 P6 N11 (A=Na, K, Rb, Cs) have been known for decades. However, their Li homologues have remained elusive. In this work, the highly condensed lithium (imido)nitridophosphates LiP4 N7 and Li3-x P6 N11-x (NH)x (x=1.66(3)) were synthesized from LiPN2 and P3 N5 in the multianvil press at 10â GPa. They constitute the first lithium nitridophosphates with 3D networks exhibiting a degree of condensation larger than 0.5 and high thermal stability. LiP4 N7 crystallizes in the orthorhombic space group P21 21 21 with a=4.5846(6)â Å, b=8.0094(11)â Å, and c=13.252(2)â Å (Z=4). Li3-x P6 N11-x (NH)x crystallizes in the triclinic space group P 1 - ${\mathrel{\mathop{{\rm { 1}}}\limits^{{\rm -}}}}$ with Z=2, a=4.6911(11)â Å, b=7.024(2)â Å, c=12.736(3)â Å, α=87.726(11), ß=80.279(11), and γ=70.551(12)°. Both compounds are stable against hydrolysis in air.
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Carbon nitrides featuring three-dimensional frameworks of CN4 tetrahedra are one of the great aspirations of materials science, expected to have a hardness greater than or comparable to diamond. After more than three decades of efforts to synthesize them, no unambiguous evidence of their existence has been delivered. Here, the high-pressure high-temperature synthesis of three carbon-nitrogen compounds, tI14-C3 N4 , hP126-C3 N4 , and tI24-CN2 , in laser-heated diamond anvil cells, is reported. Their structures are solved and refined using synchrotron single-crystal X-ray diffraction. Physical properties investigations show that these strongly covalently bonded materials, ultra-incompressible and superhard, also possess high energy density, piezoelectric, and photoluminescence properties. The novel carbon nitrides are unique among high-pressure materials, as being produced above 100 GPa they are recoverable in air at ambient conditions.
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Skutterudites are of high interest in current research due to their diversity of structures comprising empty, partially filled and filled variants, mostly based on metallic compounds. We herein present Ba12 [BN2 ]6.67 H4 , forming a non-metallic filled anti-skutterudite. It is accessed in a solid-state ampoule reaction from barium subnitride, boron nitride and barium hydride at 750 °C. Single-crystal X-ray and neutron powder diffraction data allowed to elucidate the structure in the cubic space group Im 3 â¾ ${\bar{3}}$ (no. 204). The barium and hydride atoms form a three-dimensional network consisting of corner-sharing HBa6 octahedra and Ba12 icosahedra. Slightly bent [BN2 ]3- units are located in the icosahedra and the voids in-between. 1 H and 11 B magic angle spinning (MAS) NMR experiments and vibrational spectroscopy further support the structure model. Quantum chemical calculations coincide well with experimental results and provide information about the electronic structure of Ba12 [BN2 ]6.67 H4 .
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In this work, we present the synthesis, characterization, and optical properties of Sr5Si7P2N16:Eu2+, the first tetrahedral (Si,P)-N network in which Si occupies more than 50% of the tetrahedra. While past studies have shown progress with anionic (Si,P)-N networks, the potential of silicon-rich compounds remains untapped. The synthesized compound Sr5Si7P2N16 exhibits a unique mixture of substitutional order and positional disorder within its network. The analytical challenges posed by the similarities between Si4+ and P5+, along with the network's disorder, were overcome by combining single-crystal X-ray diffraction and scanning transmission electron microscopy EDX mapping. Low-cost crystallographic calculations provided additional insights into the identification of tetrahedral occupations in mixed networks. Luminescence investigations on Sr5Si7P2N16:Eu2+ revealed yellow emission, adding to the known blue, green, and orange emission maxima of Sr-(Si,P)-N networks, highlighting the variability of such compounds.