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Hexaferrites have a wide range of technological applications as well as a rich and complicated structural chemistry, with iron oxide layers inducing highly anisotropic ferrimagnetism that remains i...

X-rays offer low tissue attenuation with high penetration depth when used in medical applications and when coupled with radioluminescent nanoparticles, offer novel theranostic opportunities. In this role, the ideal scintillator requires a high degree of crystallinity for an application relevant radioluminescence, yet a key challenge is the irreversible aggregation of the particles at most crystallization temperatures. In this communication, a high temperature multi-composite reactor (HTMcR) process was successfully developed to recrystallize monodisperse scintillating particulates by employing a core-multishell architecture. The core–shell morphology of the particles consisted of a silica core over-coated with a rare earth (Re = Y 3 + , Lu 3 + , Ce3+) oxide shell. This core–shell assembly was then encapsulated within a poly(divinylbenzene) shell which was converted to glassy carbon during the annealing & crystallization of the silica/rare earth oxide core–shell particle. This glassy carbon acted as a delamination layer and prevented the irreversible aggregation of the particles during the high temperature crystallization step. A subsequent low temperature annealing step in an air environment removed the glassy carbon and resulted in radioluminescent nanoparticles. Two monodisperse nanoparticle systems were synthesized using the HTMcR process including cerium doped Y2Si2O7 and Lu2Si2O7 with radioluminescence peaks at 427 and 399 nm, respectively. These particles may be employed as an in vivo light source for a noninvasive X-ray excited optogenetics.

The structures of seven compounds based on guanidinium cations, isolated sulfate anions, and additional organic cations and solvent molecules are reported. All seven compounds, (C(NH2)3)2(SO4) (1), (C(NH2)3)3(C5H6N)(SO4)2 (2), (C(NH2)3)3(C5H6N)(SO4)2·H2O (3), (C(NH2)3)3(C5H6N)(SO4)2·CH3OH (4), (C(NH2)3)11(C5H6N)(SO4)6·2.5C2H5OH (5), (C(NH2)3)3(C6H16N)(SO4)2 (6), and (C(NH2)3)2(C20H26N2O2)(SO4)2 (7) crystallize without a center of symmetry, and are built of related motifs of six-membered rings via hydrogen bonding of three guanidinium cations and three sulfate anions. These six-membered rings form extended sheets and frameworks through additional hydrogen bonding interactions. The presence of additional cations and solvent molecules in varying ratios add structural diversity by modifying the guanidinium sulfate frameworks, but retaining the acentricity of the structures. The study reveals a remarkable tendency for these guanidinium sulfate frameworks to crystallize without a center of symmetry, and furthermore, in polar or chiral space groups. This provides a potential pathway for the use of hydrogen bonding interactions to design structures having interesting physical or nonlinear optical properties.

An examination of manganese silicates and germanates revealed unusual structural motifs and extremely different chemistries, with identical hydrothermal reactions forming K2Mn2Si3O9 versus K11Mn21Ge32O86(OH)9(H2O). The germanate is exceptional in both its c-axis length (exceeding 76 A) and unit cell volume (nearly 18000 A3), the largest known polygermanate structure to our knowledge.

A new member of the descloizite family, a cobalt vanadate, SrCo(VO4)(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO4)(OH) crystallizes in the orthorhombic crystal system in space group P212121 with the following unit cell parameters: a = 6.0157(2) A, b = 7.645(2) A, c = 9.291(3) A, V = 427.29(2) A3, and Z = 4. It contains one-dimensional Co-O-Co chains of edge-sharing CoO6 octahedra along the a-axis connected to each other via VO4 tetrahedra along the b-axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO4)(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co2+ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO6 octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a-axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO4)(OH).

A novel technique for the absolute stereochemical determination of alcohols has been developed that uses crystallization of guanidinium salts of organosulfates. The simple one-pot, two-step process leverages facile formation of guandinium organosulfate single crystals for the straightforward determination of the absolute stereochemistry of enantiopure alcohols by means of X-ray crystallography. The strong hydrogen bonding network drives the stability of the crystal lattice and allows for a diverse range of organic alcohol substrates to be analyzed.

Materials with triangular arrangements of transition metal ions are of great interest for their complex magnetism resulting from geometric frustration. This paper describes the stepwise formation of kagome lattices of open shell transition-metal ions from half-delta chains to delta/sawtooth chains, and finally kagome nets. The systems can be viewed as a testbed for magnetic studies since a variety of spin states can be introduced across the same structure type, and progress through increasing levels of structural complexity and dimensionality. The synthetic and structural development of this continuum is studied here in well-formed single crystals of A2 M3 (MoO4 )3 (OH)2 (A=K, Rb; M=Mn, Co), CsM2 (MoO4 )2 (OH) (M=Mn, Fe, Co, Zn), and KM3 (MoO4 )2 O(OH) (M=Mn).

A hydrothermal route to single crystals of rare earth stannates RE2Sn2O7 (RE = La–Lu) in the cubic pyrochlore structure is reported. Growth reactions were performed in aqueous fluids at 700 °C and 200 MPa with CsF mineralizers in concentrations ranging from 0 to 30 M, with 20 M CsF providing the most consistent results. Single crystals of the entire range of lanthanides were grown and characterized by single crystal X-ray diffraction and found to be isostructural in the Fd3m space group. The unit cell sizes range from 10.7106(16) A for La2Sn2O7 to 10.3005(9) A for Lu2Sn2O7. Both the unit cell size and RE–O distances are found to be essentially linear with respect to the ionic radius of the rare earth ion. The high quality diffraction data strongly suggests that there is very little site disorder or lattice defects in the sample. Of particular interest is the synthesis and single crystal growth of Ce2Sn2O7, which represents one of the few f1 pyrochlore samples. Specific heat measurements were obtained dow...

The reactions of Ln2O3 (Ln = La Lu) with ReO2 were examined in high temperature hydrothermal water (650 °C). In all cases the rhenium oxide was added in a three-fold excess. No external mineralizer was needed and the rhenate itself acted as a sufficient mineralizer to form high quality single crystals of several crystalline products. These form in good yield with compositions varying as a function of the size of the rare earth ion. The largest sesquioxide, La2O3, forms the well-known La4Re6O19 phase, but when Ln = Nd or Pr, a new product, Ln2Re2O7(OH), is isolated. Reactions with Ln = Sm Tb form Ln4Re2O11, and those with Dy Lu form Ln2ReO5. The new Ln2Re2O7(OH) series was characterized as a new structure type by single crystal X-ray diffraction. This structure features a tetrameric Re4O16 cluster embedded in a lanthanide oxide framework. Additional detailed structural data is also provided for Tb4Re2O11 and Eu4Re2O11, which were not previously reported for the Ln4Re2O11 family. In Ln2Re2O7(OH), no direct Re Re bond (Re Re = 2.60 A) is observed while Ln4Re2O11 appears to possess a rhenium-rhenium double bond with a Re Re distance of 2.42 A. Single crystal Raman data supports both of these characterizations. Magnetic data is reported for Ln2Re2O7(OH) and Tb4Re2O11, and their behavior appears to be dominated by the f-element magnetic moments. At low temperatures Tb4Re2O11 displays possible canted antiferromagnetic coupling.

Two new structurally related cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method utilizing halide brine mineralizers. Both structures Cs6Mn(H2O)2(VO3)8 (I) and Cs5KMn(H2O)2(VO3)8 (II) are isostructural crystallizing in the tetragonal space group P4/mnc. The first structure, Cs6Mn(H2O)2(VO3)8 (I) has unit cell dimensions of a = 13.6830(4) A, c = 8.6476(3) A and the second structure, Cs5KMn(H2O)2(VO3)8 (II), has unit cell dimensions of a = 13.5015(4) A, c = 8.5372(3) A. The structures are built from a manganese vanadate chain, which consists of [Mn(H2O)2O4] units that are coordinated to one another by a unique sinusoidal vanadate chain, (VO3)n. Both structures have well-ordered alkali metal atoms, with the potassium atoms of II exhibiting preferential site occupancy. Both compounds were characterized by single crystal X-ray diffraction and infrared spectroscopy, to identify the characteristic O–H and V–O modes. Crystals of Cs6Mn(H2O)2(VO3)8 and Cs5KMn(H2O)2(VO3)8 were synthesized from hydrothermal brines and their structures determined by single crystal X-ray diffraction, revealing preferential, ordered site substitution of the alkali metals.

Two new structural types of BaREGeO4(OH) and BaRE10(GeO4)4O8 (RE = Ho3+,Er3+) single crystals were synthesized via high-temperature and high-pressure hydrothermal synthesis. The BaREGeO4(OH) compounds were found to crystallize in the orthorhombic space group Pbca. BaHoGeO4(OH) is used as a representative of the family with cell parameters of a = 5.7175(2) A, b = 10.1556(5) A, c = 10.6189(9) A and V = 964.97(8) A3. The BaREGeO4(OH) structure contains a one-dimensional chain of rare-earth polyhedra linked through edge sharing of oxygen atoms. High density BaRE10(GeO4)4O8 crystals crystallize in the monoclinic space group C2/m and feature a sheet like arrangement of rare-earth oxide polyhedra with Keggin-like features. BaHo10(GeO4)4O8 is used as a representative of this structure type with cell parameters of a = 12.4533(8) A, b = 7.2008(5) A, c = 12.0034(8) A, β = 100.183(2)⁰ and V = 1059.43(12) A3. Barium polyhedra and isolated GeO4 units aid in connecting the rare earth oxide framework to extend it in three-dimensional (3-D) space. Characterization by single crystal X-ray diffraction and Raman and photoluminescence spectroscopies is reported.

The magnetic properties are reported for three members of the glaserite series of compounds, Na2BaM(VO4)2, M = Mn, Mn0.6Co0.4, and Co. Large single crystals are grown using a high-temperature hydrothermal synthesis method. This structure type exhibits a triangular magnetic lattice in which M2+O6 octahedra are interconnected with nonmagnetic (VO4)3- groups. All the structures crystallize at room temperature with rigid trigonal symmetry (space group P3 m1); however, at lower temperatures both Na2BaMn(VO4)2 and Na2BaMn0.6Co0.4(VO4)2 undergo a structural transition to lower symmetry (monoclinic, C2/ c). The bulk magnetic measurements indicate that Mn- and Co-structures are antiferromagnetic and ferromagnetic, respectively. Na2BaMn0.6Co0.4(VO4)2 does not show any long-range ordering down to 0.5 K, although a broad heat capacity anomaly near 1.2 K suggests short-range magnetic order or freezing into a spin-glass-like state related to the chemical disorder and resulting competing magnetic interactions. The magnetic structures of Na2BaMn(VO4)2 and Na2BaCo(VO4)2 were determined using neutron powder diffraction. At zero magnetic field, Na2BaMn(VO4)2 possesses an antiferromagnetic structure with the moments ordered in a Neel-type arrangement and aligned along the C4 axis of the octahedra. Under applied magnetic field at 0.3 K, the evolution of the magnetic structure toward a fully polarized state is observed. Na2BaCo(VO4)2 represents a ferromagnetic (FM) magnetic structure with Co moments aligned parallel to the c-axis direction. The relationships between these structures and magnetic properties are discussed.

Reactions are reported of early rare earth oxides, RE2O3 (RE = La, Pr, Nd) with Ta2O5 under hydrothermal conditions (650 °C, 1.5 kbar) in concentrated aqueous hydroxide (20-30 M KOH) as a mineralizer. Under various stoichiometries several members of two new structure types were isolated, Ln2TaO5(OH) (Ln = La, Pr) and Ln3Ta2O9(OH) (Ln = Pr, Nd). The analogous niobate La2NbO5(OH) was also obtained. Both structure types were characterized by single crystal X-ray diffraction and contain pentavalent tantalatum oxide octahedra and complex rare earth oxide frameworks. The Ln2TaO5(OH) structure type contains Ln-O8 and Ln-O9 building blocks and TaO6 octahedra in a 3-D framework. It contains a 3-D rare earth oxide framework formed by from zig-zag chains of rare earth oxides linking sheets of rare earth oxides. The tantalates form edge-shared Ta2O10 dimers occupying gaps in the rare earth oxide frameworks. The structure of Ln3Ta2O9(OH) contains two types of 2-D rare earth oxide slabs built of seven and eight coordinate rare earth metals. The tantalate units form 2-D slabs through a multiple corner-sharing scheme of TaO6 octahedra. The Ln3Ta2O9(OH) structure type has an interesting close structural relationship to the previously reported rare earth titanate La5Ti4O15(OH), which is discussed. The presence of hydroxide in the lattice is confirmed by IR spectroscopy and the H atom locations are assigned unambiguously using bond valence sums.

The current effort demonstrates that lutetium oxyorthosilicate doped with 1–10% cerium (Lu2SiO5:Ce, LSO:Ce) radioluminescent particles can be coated with a single dye or multiple dyes and generate an effective energy transfer between the core and dye(s) when excited via X-rays. LSO:Ce particles were surface modified with an alkyne modified naphthalimide (6-piperidin-1-yl-2-prop-2-yn-1-yl-1H-benzo[de]isoquinoline-1,3-(2H)-dione, AlNap) and alkyne modified rhodamine B (N-(6-diethylamino)-9-{2-[(prop-2-yn-1-yloxy)carbonyl]phenyl}-3H-xanthen-3-ylidene)-N-ethylethanaminium, AlRhod) derivatives to tune the X-ray excited optical luminescence from blue to green to red using Forster Resonance Energy Transfer (FRET). As X-rays penetrate tissue much more effectively than UV/visible light, the fluorophore modified phosphors may have applications as bioimaging agents. To that end, the phosphors were incubated with rat cortical neurons and imaged after 24 h. The LSO:Ce surface modified with AlNap was able to be success...

Large single crystals of Yb2Ge2O7 in the cubic Fd3m space group, are synthesized and characterized from a high-temperature hydrothermal method (650°C/200 MPa in 1 M KF). The cubic phase displays spin frustration and possibly nonclassical quantum-spin behavior at low temperature. This is the first report of single crystals of this important phase of size and quality suitable for single-crystal neutron diffraction.

The growth of large high quality single crystals of three lithium silicates and germanates Li 2 SiO 3 , Li 2 SiO 5 , and Li 2 GeO 3 is described. The crystals are all grown using hydrothermal fluids at 650 °C and 1 kbar using simple oxide feedstock and 3–6 M LiOH serving as both the lithium ion source and mineralizer. The crystals could be grown by spontaneous transport without any specific seeding, and grew between 2 and 10 mm/edge and without evidence of cracking, physical twinning or multiple domain structures. The crystals were characterized by single crystal diffraction, UV–vis spectroscopy and Raman spectroscopy. All the crystals are acentric and polar. Preliminary nonlinear optical properties were investigated using the Kurtz method and indicate that the crystals exhibit Type-1 phase matching ability, and Li 2 SiO 3 demonstrates a significant nonlinear optical conversion efficiency, making it of potential interest as a UV NLO crystal.

The structure of Cs3 RESi6 O15 , where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6 O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 A) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 °C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.

Reactions of rare-earth oxides with TiO2 were performed in high temperature (650–700 °C) hydrothermal fluids. Two different mineralizer fluids were examined, 20 M KOH and 30 M CsF, and their respective products analyzed. When concentrated KOH fluids were used, single crystals of a variety of new OH− containing species were isolated and structurally characterized: RE5Ti4O15(OH) (RE = La, Er) I, Sm3TiO5(OH)3II and RE5Ti2O11(OH) (RE = Tm–Lu) III. La5Ti4O15(OH) I crystallizes in the orthorhombic space group Pnnm with unit cell dimensions of a = 30.5152(12) A, b = 5.5832(2) A, c = 7.7590(3) A and V = 1321.92(9) A3, Z = 4. Sm3TiO5(OH)3II crystallizes in the monoclinic space group P21/m with unit cell parameters of a = 5.6066(2) A, b = 10.4622(4) A, c = 6.1258(2) A and β = 104.7390(10)°, V = 347.50(2) A3, Z = 2. Lu5Ti2O11(OH) III crystallizes in the monoclinic space group C2/m with unit cell dimensions of a = 12.1252(9) A, b = 5.8243(4) A, c = 7.0407(5) A, β = 106.939(3)° and V = 475.65(6) A3, Z = 2. When concentrated fluoride solutions are used, mostly RE2Ti2O7 type compounds were isolated in either cubic or monoclinic phases. In the case of cerium, Ce2Ti4O11IV was isolated that crystallizes in the monoclinic space group C2/c with unit cell parameters of a = 13.6875(7) A, b = 5.0955(3) A, c = 12.8592(7) A, β = 108.964(2)° and V = 848.18(8) A3, Z = 4. The synthesis, structural characterization, and supporting characterization are reported for all compounds. The work highlights the complementary nature of hydroxide and fluoride fluids in studying the reactivity of refractory oxides.

Two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions. One compound, Cs3Mn(VO3)4Cl, (1) was prepared using a mixed cesium hydroxide/chloride mineralizer, and crystallizes in the polar noncentrosymmetric space group Cmm2, with a = 16.7820(8) A, b = 8.4765(4) A, c = 5.7867(3) A. This structure is built from sinusoidal zig-zag (VO3)n chains that run along the b-axis and are coordinated to Mn2+ containing (MnO4Cl) square-pyramidal units that are linked together to form layers. The cesium cations reside between the layers, but also coordinate to the chloride ion, forming a cesium chloride chain that also propagates along the b-axis. The other compound, Cs2Mn(VO3)3F, (2) crystallizes in space group Pbca with a = 7.4286(2) A, b = 15.0175(5) A, c = 19.6957(7) A, and was prepared using a cesium fluoride mineralizer. The structure is comprised of corner sharing octahedral Mn2+ chains, with trans fluoride ligands acting as bridging units, whose ends are capped by (VO3)n vanadate chains to form slabs. The cesium atoms reside between the manganese vanadate layers, and also play an integral part in the structure, forming a cesium fluoride chain that runs along the b-axis. Both compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and single-crystal Raman spectroscopy. Additionally, the magnetic properties of 2 were investigated. Above 50 K, it displays behavior typical of a low dimensional system with antiferromagnetic interactions, as to be expected for linear chains of manganese(ii) within the crystal structure.

The structural and magnetic properties of a glaserite-type Na2BaFe(VO4)2 compound, featuring a triangular magnetic lattice of Fe2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal P3m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (Ts = 288 K). This structural transition involves a tilting of Fe-O-V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na2BaFe(VO4)2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Overall, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO6 octahedron.

Three new strontium manganese vanadates, Sr 2 Mn 2 (V 3 O 10 )(VO 4 ) ( I ), Sr 3 Mn(V 2 O 7 ) 2 ( II ), and Sr 2 Mn(VO 4 ) 2 (OH) ( III ), were prepared using a high temperature (580 °C) hydrothermal method with various chloride salts as the mineralizer. Minor differences in the chloride stoichiometry led to significant differences in product. Compound I crystallizes in the monoclinic space group P 2 1 / c ( a = 6.8773(12) A, b = 15.061(3) A, c = 11.609(2) A, β = 96.745(8)°), and consists of edge-shared octahedral manganese(II) dimers coordinated by trimeric [V 3 O 10 ] and monomeric [VO 4 ] groups. Compound II crystallizes in the tetragonal crystal system, P 4 3 2 1 2 ( a = 6.9951(2) A, c = 25.4390(7) A), and is built from monomeric manganese(II) octahedra chelated by two pyrovanadate [V 2 O 7 ] groups and linked to each other by additional pyrovanadates to form layers. Compound III is a noncentrosymmetric variation on the brackebuschite structure type, crystallizing in the monoclinic space group P 2 1 ( a = 7.6316(3) A, b = 6.1204(3) A, c = 8.6893(3) A, β = 111.3940(10)°). The structure is composed of octahedral manganese(III) edge-sharing chains coordinated to corner-sharing monomeric [VO 4 ] groups, thereby forming a manganese vanadate chain. All compounds were characterized by single-crystal X-Ray diffraction, powder X-Ray diffraction, infrared spectroscopy and single-crystal Raman spectroscopy. Density functional theory calculations were employed to investigate the relative stability of compound III .

Structural variations across a series of barium rare earth (RE) tetrasilicates are studied. Two different formulas are observed, namely those of a new cyclo-silicate fluoride, BaRE2Si4O12F2 (RE = Er3+–Lu3+) and new compounds in the Ba2RE2Si4O13 (RE = La3+–Ho3+) family, covering the whole range of ionic radii for the rare earth ions. The Ba2RE2Si4O13 series is further subdivided into two polymorphs, also showing a dependence on rare earth ionic radius (space group P{\overline 1} for La3+–Nd3+, and space group C2/c for Sm3+–Ho3+). Two of the structure types identified are based on dinuclear rare earth units that differ in their crystal chemistries, particularly with respect to the role of fluorine as a structural director. The broad study of rare earth ions provides greater insight into understanding structural variations within silicate frameworks and the nature of f-block incorporation in oxyanion frameworks. The single crystals are grown from high-temperature (ca 953 K) hydrothermal fluids, demonstrating the versatility of the technique to access new phases containing recalcitrant rare earth oxides, enabling the study of structural trends.

Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using Tb4O7 as a starting material. Tb13(GeO4)6O7(OH) crystallizes in trigonal space group R3, is built up of isolated GeO4 units, and contains a complex arrangement of terbium oxide polyhedra. K2TbGe2O7 is a terbium(4+) pyrogermanate that is isostructural with K2ZrGe2O7 and displays a rare stable Tb4+ oxidation state in the solid state.

Crystals of ASr2V3O3(Ge4O13)Cl, A = Na, K, were synthesized from high-temperature hydrothermal brines, and their structure and magnetic properties were investigated. These materials present a unique combination of a salt inclusion lattice, a polar crystal structure, and isolated V4+ (S = 1/2) trimer magnetic clusters. The structures consist of a trimeric V3O13 unit based on V4+ (S = 1/2), having rigorous 3-fold symmetry with a short V–V separation of 3.325(3) A. The trinuclear V4+ units are formed by three edge shared VO6 octahedra sharing a central μ3-oxygen atom, which also imparts a polar sense on the structure. The V3O13 units are isolated from one another by tetranuclear Ge4O13 units, which are similarly arranged in a polar fashion, providing a unique opportunity to study the magnetic behavior of this triangular d1 system as a discrete unit. Magnetization measurements indicate spin-1/2 per V atom at high temperature, and spin-1/2 per V3 trimer at low temperature, where two V moments in each triangle ...

Manganese vanadate fluorides were synthesized using high-temperature hydrothermal techniques with BaF2 as a mineralizer. Ba3Mn2(V2O7)2F2 crystallizes in space group C2/c and consists of dimers built from edge-sharing MnO4F2 trigonal prisms with linking V2O7 groups. Ba7Mn8O2(VO4)2F23 crystallizes in space group Cmmm, with a manganese oxyfluoride network built from edge- and corner-sharing Mn2+/3+(O,F)6 octahedra. These octahedra form alternating Mn2+ and Mn2+/3+ layers separated by VO4 tetrahedra. This latter compound exhibits a canted antiferromagnetic order below TN = 25 K.

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) A, b=11.574(3) A, c=10.914(2) A; Cs2Mn2V2O7F2: a=7.5615(15) A, b=11.745(2) A, c=11.127(2) A). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neel temperature, TN=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) A, b=6.8036(7) A, c=10.1408(13) A and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

A convenient hydrothermal route to high quality single crystals of rare earth orthoniobates RENbO4 (RE = Y, La–Lu) is reported. The title compounds can be grown as single crystals in sizes exceeding 2 mm for most of the rare earths using 30 M KOH at temperatures of 700 °C and pressures of 2 kbar. Single crystal X-ray diffraction shows that they all form in the fergusonite structure type, and the structures were solved in space group C2/c. Examples based on the largest and smallest rare earth ions in the present study include LaNbO4: a = 7.3576(15) A, b = 11.538(2) A, c = 5.2128(10) A, β = 130.900(3)°, Z = 4, R1 = 0.0162, wR2 = 0.0405, and LuNbO4: a = 6.9805(6) A, b = 10.8271(8) A, c = 5.0406(4) A, β = 131.676(3)°, Z = 4, R1 = 0.0178, wR2 = 0.0489. Although domain structures are clearly present in the bulk crystals, the domains are much larger than normally reported from high temperature growth methods, and individual single domain crystals on the order of 0.1–1 mm in size can be selected. Rocking curves o...

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) Å, b = 9.5627(9) Å, c = 5.4139(6) Å, β = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) Å, b = 6.4678(8) Å, c = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn-O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal [MnO5] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO6] octahedra, and these sublattices are connected through edge-shared dimers of [MnO5] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie-Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn5(VO4)2(OH)4 and below 45 K in Mn6O(VO4)2(OH). Members of another class of compounds, K2M3(VO4)2(OH)2 (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals.

As intermediate products of the dehydration of hydroxides or the hydration of oxides, rare earth oxyhydroxides (REOOH) have important implications for synthesis and potential applications in luminescent devices. Using high temperature oxide melt solution calorimetry and thermal analysis, thermodynamic properties of REOOH (RE ​= ​Eu to Lu), including enthalpies of dehydration and formation, were determined. The exothermic enthalpies of formation from oxides and endothermic enthalpies of dehydration demonstrate that oxyhydroxides are not only synthetic but also thermodynamic intermediates in rare earth oxide - water systems. The linear relationship between enthalpies of formation from oxides and ionic radius of RE3+ confirms the key role of cation size in the stability of REOOH, and reveals that REOOH with lighter rare earth elements are easier to form and harder to dehydrate, both thermodynamically and kinetically.

A method for the synthesis of single crystals of BaSnO3 is reported. The growth employs a hydrothermal process using simple Ba(OH)2 and SnO2 powders in water at 650 °C and 140 MPa, with 5 M CsOH mineralizer in welded inert metal liners. Solubility studies indicate that the crystals have positive solubility coefficients that increase with temperature and mineralizer concentration in the growth regimes investigated. The tetravalent tin ions are somewhat aggressive toward the inert metal liners, especially silver and gold, requiring platinum liners for longer term growth runs. The (1 1 0) and (1 0 0) faces are commonly observed on the as-grown crystals. The crystals are thermally and chemically stable and can be readily polished as substrates for subsequent epitaxial growth. Crystals that are n-doped (La:BaSnO3) can be grown by the addition of the desired amount of La2O3 to the initial feedstock. The band gap for this hydrothermally-grown BaSnO3 was measured using the Tauc plot method to be 2.94 eV, with approximately 0.3 eV shift to higher energy upon n-doping.

The solid-state chemistry of novel metal silicate and borosilicate crystals containing Eu2+ and Eu3+ in high temperature hydrothermal fluids was investigated. It was found that europium ions could be readily incorporated into a number of crystals using a variety of simple glass-based feedstocks. The hydrothermal growth reactions were performed at nearly 600 °C in 1–5 M NaOH mineralizer fluids, and this was found to be a versatile route to both europium ion oxidation states with Eu acting as either a fundamental structural building block or a dopant ion. Several new single crystals were identified including two new apatites as well as a new europium borosilicate. The apatites crystallize in space group P63/m with a = 9.4619(13) A and c = 7.0054(14) A for Eu10(SiO4)6O2, and a = 9.4413(13) A and c = 6.9087(14) A for NaEu9(SiO4)6O2. The new borosilicate, Eu2SiB2O8, crystallizes in space group Pbcn with a = 13.310(3) A, b = 4.4247(9) A and c = 9.2394(18) A. The investigation of Eu-doped borosilicates demonstrated the strong blue emission generated from 370 nm excitation that was expected for the Eu2+ doped materials, as well as the less intense orange-red emission expected for the Eu3+ dopants. The hydrothermal reactions naturally facilitated a degree of europium reduction in Eu:Ba3Si2B6O16. It was found that the oxidation states of europium in the final product could be further controlled by using hydrazine as a reducing reagent.

The structural variations of several alkali metal rare earth fluoride single crystals are summarized. Two different stoichiometric formulations are considered, namely those of ARE2F7 and ARE3F10 (A = K, Rb, Cs; RE = Y, La–Lu), over a wide range of ionic radii of both the alkali and rare earth (RE) ions. Previously reported and several new single-crystal structures are considered. The new single crystals are grown using hydrothermal methods and the structures are compared with literature reports of structures grown from both melts and hydrothermal fluids. The data reported here are combined with the literature data to gain a greater understanding of structural subtleties surrounding these systems. The work underscores the importance of the size of the cations to the observed structure type and also introduces synthetic technique as a contributor to the same. New insights based on single-crystal structure analysis in the work introduce a new disordered structure type in the case of ARE2F7, and examine the trends and boundaries of the ARE3F10 stoichiometry. Such fundamental structural information is useful in understanding the potential applications of these compounds as optical materials.

The study of Ce4+ as a building block using CeF4 as a reagent in hydrothermal synthesis has resulted in several new cerium oxyfluorides that have been structurally characterized by single crystal X-ray diffraction. Two families of compounds are represented: ACe3OF11 (A = K, Rb, NH4), and A2Ce3OF12 (A = Cs). The ACe3OF11 compounds represent a new structure type crystallizing in space group P-6m2 with a = 7.9794(11) A and c = 8.2513(17) A for KCe3OF11, a = 8.0351(11) A and c = 8.3077(17) A for RbCe3OF11, and a = 8.0457(11) A and c = 8.2918(17) A for (NH4)Ce3OF11. The structure of Cs2Ce3OF12 conforms to the same structure type as several other A2M3OF12 (A = K, Rb, Tl; M = Hf, Zr) compounds in space group R-3m, and has unit cell parameters of a = 8.2663(12) A and c = 31.851(6) A. The two structures form different cerium oxyfluoride frameworks to accommodate the monovalent cations in different ways. Formation of the different oxyfluoride phases is thus sensitive to the size ratio of the monovalent and tetravalent cations. Synthesis of the ACe3OF11 phases has enabled a comparative analysis of the crystal chemistry across these two families of compounds, and several trends and limitations of the two structure types are identified. The hydrothermal synthesis of oxyfluorides having compositions ACe3OF11 (A = K, Rb, NH4) and A2Ce3OF12 (A = Cs) is described. Structural comparisons are made between the two structure types, and crystal chemical relationships pertaining to their preferential formation are identified based on a broader examination of their constituent monovalent and tetravalent cations. The ACe3OF11 structure type is a new structure type enabled by the size of the Ce4+ cation.

A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

An investigation into the crystal chemistry of the alkali thorium silicates resulted in the formation of five novel materials by hydrothermal synthesis. Of these, Rb4Th2Si12O30, and K2ThSi4O10F2 are new structure types crystallizing in space groups P1 and Pnma, respectively. The structure of Rb4Th2Si12O30 reveals a silicate sheet structure with eight-, six-, five-, and four-membered silicate rings. Crystals of a related composition, Cs2ThSi6O15, were also synthesized. They crystallize in space group Cmc21 and have a silicate sheet containing eight-, six-, and four-membered silicate rings. The structure of K2ThSi4O10F2 consists of a tubular silicate column comprised of eight-, six-, and four-membered silicate rings and features chains of fluorine-bridged Th atoms. Two new wadeite analogues Cs2ThSi3O9 and Rb2ThSi3O9 were also discovered and constitute the first actinide representatives in this mineral family. All products were crystallized from reactions of ThO2 and silica with alkali fluorides or hydroxid...

Single crystals of LiKTmF 5 were grown hydrothermally. Its crystal structure was studied with single-crystal X-ray diffraction to 8.6 GPa. The material is monoclinic (P2 1 /c, Z = 4) and does not undergo any phase transition in the pressure range studied here. The analysis of its pseudosymmetry with respect to the minimal k -supergroup C2/m reveals that the deviations of the individual atoms from the respective higher symmetrical positions in C2/m are increasing on compression, i.e., due to the reduction of the unit-cell volume. Such a behaviour is the opposite of the effect of incorporation of various M cations in the LiKMF 5 materials (M:Y and rare earths) at atmospheric conditions, since LiKYbF 5 and LiKLuF 5 with the smallest unit cells crystallize in space group C2/m, while LiLYF 5 with a larger unit cell has P2 1 /c symmetry.

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V2O7]4– groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl2/Ba(OH)2 mineralizer, and the third compound was prepared from BaCl2 mineralizer. An interesting structural similarity exists between two of the compounds, Ba2Mn(V2O7)(OH)Cl and Ba4Mn2(V2O7)(VO4)2O(OH)Cl. These two compounds crystallize in the orthorhombic space group Pnma, Z = 4, and are structurally related by a nearly doubled a axis. The first structure, Ba2Mn(V2O7)(OH)Cl (I) (a = 15.097(3) A, b = 6.1087(12) A, c = 9.5599(19) A), consists of octahedral manganese(II) edge-sharing chains linked by pyrovanadate [V2O7] groups, generating a three-dimensional structure. Compound II, Ba4Mn2(V2O7)(VO4)2O(OH)Cl (a = 29.0814(11) A, b = 6.2089(2) A, c = 9.5219(4) A), is composed of manganese(III) edge-sharing chains that are coordinated to one another through pyrovanadat...

Two new monovalent metal thorium fluorides and three new monovalent metal cerium fluorides have been synthesized hydrothermally and structurally characterized. The structures of the five compounds are described in space group $${\text{R}}\bar{3}$$ : Tl7Th6F31 with a = 15.598(2) and c = 10.893(2), (NH4)7Th6F31 with a = 15.5979(2) and c = 10.952(2), K7Ce6F31 with a = 15.013(2) and c = 10.295(2), (NH4)7Ce6F31 with a = 15.232(2) and c = 10.749(2), and Na7Ce6F31 with a = 14.567(2) and c = 9.6921(19). Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be largely dependent upon the concentration of the monovalent fluoride mineralizer solution and thus, the ratio of monovalent ions to thorium or cerium in the system. The crystal chemistry of the A7B6F31 (A = Na+, K+, Rb+, Tl+, NH4 +; B = Zr4+, Ce4+, Th4+) structure type is described by examining the title compounds alongside other isomorphs to gain a broader understanding of the crystallization of complex fluorides. Structural subtleties are also discussed, including substitutional disorder of Na+ and Ce4+ cations in Na7Ce6F31. The hydrothermal synthesis of fluorides having compositions A7B6F31 (A = Na, K, NH4, Tl; B = Ce, Th) is described. Structural comparisons are made to discuss the crystal chemistry within this family of compounds in terms of the combinations of A and B cations supported by the structure type. The study introduces Tl+ and NH4 + as new A-site building blocks, and Ce4+ as a new B-site building block for this structure type.

We have investigated the hydrothermal growth of, and spectrally characterized, the lutetium based laser materials Nd:LuAG, Yb:LuAG, and Yb:Lu2O3. Absorption cross-section data are presented for Nd:LuAG at 83, 175, and 295 K. Absorption cross-section data was also obtained for Yb:LuAG at 83, 175, and 295 K; the 295 K data was used to generate emission cross-sections using the method of reciprocity. For Yb:Lu2O3, we present absorption cross-sections at 295 K as well as emission cross-sections derived using reciprocity.

Single crystals of thorium dioxide ThO2, grown by the hydrothermal growth technique, have been investigated by ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), and L3, M3, M4, and M5 X-ray absorption near edge spectroscopy (XANES). The experimental band gap for large single crystals has been determined to be 6 eV to 7 eV, from UPS and IPES, in line with expectations. The combined UPS and IPES, place the Fermi level near the conduction band minimum, making these crystals n-type, with extensive band tailing, suggesting an optical gap in the region of 4.8 eV for excitations from occupied to unoccupied edge states. Hybridization between the Th 6d/5f bands with O 2p is strongly implicated. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Potassium yttrium double vanadates (K3Y(VO4)2) doped with Bi3+ or Dy3+ and codoped with Bi3+ and Dy3+ have been synthesized by solid state reactions at 1000 °C for 48 h and their photoluminescence properties investigated. Efficient energy transfer from the vanadate (VO43−) group or bismuth ions to the rare earth ion has been established by photoluminescence investigation upon UV excitation and results in blue and yellow emissions at 480–489 nm and 572–580 nm respectively. The codoping of Bi3+ and Dy3+ into K3Y(VO4)2 results in enhanced yellow emission band while the blue emission band remains relatively unchanged. The intensities of emission for the studied materials were investigated as a function of different Bi3+ and Dy3+ ion concentrations. The presented results show K3Y(VO4)2 phosphors as potential candidates W-LEDs applications.

Several new borate compounds, Ba11B26O44(PO4)2(OH)6 (1), Li9BaB15O27(CO3) (2), and Ba3Si2B6O16 (3) were synthesized containing other hetero-oxyanion building blocks in addition to the borate frameworks. They were all prepared under hydrothermal conditions and characterized by single crystal and powder X-ray diffraction, and IR spectroscopy. Crystal data: For 1; space group P21/c, a=6.8909 (14) A, b=13.629 (3) A, c=25.851 (5) A, β=90.04 (3)°; For 2; space group P-31c, a=8.8599 (13) A, c=15.148 (3) A; For 3; space group P-1, a=5.0414 (10) A, b=7.5602 (15) A, c=8.5374 (17) A, α=77.15 (3)°, β=77.84 (3)°, γ=87.41 (3)° for 3. Compounds 1 and 2 contain isolated oxyanions [PO4]3− and [CO3]2− respectively, sitting in channels created by the borate framework, while structure 3 has the [SiO4]4− groups directly bonded to the borate groups creating a B–O–Si framework.

K2ThF6 and K7Th6F31 were prepared hydrothermally as single crystals. Their structures were investigated with single-crystal X-ray diffraction at ambient conditions and at high pressures using diamond anvil cells. The results of this study indicate that the two materials, with chains of face-sharing tricapped trigonal prisms ThF9 and with layers of square antiprisms ThF8 sharing their edges in Th2F14 doublets, respectively, are structurally stable at least to about 9 GPa at room temperature. This observation suggests that, in general, moderate high pressure has no effect on the coordination polyhedra around the Th atoms and the topology of the structure of complex thorium fluorides. The bulk compressibility of the thorium fluorides entirely depends on the alkali metal present in the structure.

The hydrothermal synthesis and crystal growth of LiLuF 4 were investigated. Small crystals of LiLuF 4 were produced but while investigating various alkali fluoride mineralizers, a new series of alkali lithium lutetium fluorides, including, LiKLuF 5 and LiNaLu 2 F 8 , were synthesized under hydrothermal conditions (570 °C at 12.5 kpsi). The mineralizer KF leads to formation of a new compound LiKLuF 5 crystallized in the space group C 2/ m with the lattice parameters a = 6.2328(12), b = 11.709(2), c = 6.3986(13), β = 113.87(3). Tm and Yb analogs were also synthesized using the same conditions. Use of NaF as mineralizer leads to a new compound LiNaLu 2 F 8 , crystallized in space group Cmcm , a = 10.3181(21), b = 8.2393(16), c = 6.9565(14). Several doped compounds were also isolated and electronic spectra were obtained.

Single crystals of (Li5.5Fe0.5)FeCaB12O24 (1), (Li5.5Fe0.5)FeSrB12O24 (2) and (Li5.5Fe0.5)FeBaB12O24 (3) were hydrothermally prepared and structurally characterized by single crystal X-ray diffraction, powder X-ray diffraction, infrared and UV-visible diffuse reflectance spectroscopy. These compounds crystallize in space group R-3 with cell parameters of a = 14.705(2) A and c = 6.4633(13) A for 1, a = 14.679(2) A and c = 6.5320(13) A for 2, and a = 14.662(2) A and c = 6.6224(13) A for 3. The structures are built of helical chains consisting of BO4 tetrahedra and BO3 triangles linked via common vertices. The title compounds are isostructural with a known lithium lead iron hexaborate, (Li5.5Fe0.5)FePbB12O24 and structural comparisons are made within this family of compounds. The hydrothermal synthesis and characterization of three new iron hexaborates, (Li5.5Fe0.5)FeCaB12O24, (Li5.5Fe0.5)FeSrB12O24 and (Li5.5Fe0.5)FeBaB12O24 are discussed. Structural comparisons are made between these new structures and a previously reported lithium lead iron hexaborate, (Li5.5Fe0.5)FePbB12O24.

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) A, b = 9.5627(9) A, c = 5.4139(6) A, β = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) A, b = 6.4678(8) A, c = 10.4478(13) A, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn–O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal...