New Series of Red-Light Phosphor Ca9-xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0-1).

In this study, a new series of phosphors, Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0.00−1.00, step dx 0.05), was synthesized, consisting of centro- and non-centrosymmetric phases with ß-Ca3(PO4)2-type structure. Crystal structures with space groups R3c (0.00 ≤ x < 0.35) and R3¯c (x > 0.8) were determined using X-ray powder diffraction and the method of optical second harmonic generation. In the region 0.35 ≤ x ≤ 0.75, phases R3c and R3¯c were present simultaneously. Refinement of the Ca8ZnGd(PO4)7 crystal structure with the Rietveld method showed that 71% of Gd3+ ions are in M3 sites and 29% are in M1 sites. A luminescent spectroscopy study of Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ indicated the energy transfer from the crystalline host to the Gd3+ and Eu3+ luminescent centers. The maximum Eu3+ luminescence intensity corresponds to the composition with x = 1.

Coordination Properties of Hydroxyisophthalic Acids: Topological Correlations, Synthesis, Structural Analysis, and Properties of New Complexes.

Hydroxyisophthalic acids are valuable polytopic ligands for the design of functional materials based on coordination polymers due to the variety of charges and coordination modes they possess. Herein, we describe the synthesis, thermal stability, nonlinear optical (NLO) and spectroscopic properties of five novel coordination compounds, [K2 L(H2 O)2 ], [MgL(H2 O)2 ] ⋅ 3H2 O, [CaL(H2 O)3 ], [SrL(H2 O)3 ] ⋅ H2 O, [BaL(H2 O)(H2 O)5 ], and one salt, (NH4 )2 L ⋅ 2H2 O, with 4,5,6-trihydroxyisophthalic acid (H2 L), which has not been tested in assembling crystalline coordination networks before. The peculiarities of the structural organization of the compounds were analyzed and compared with those for other hydroxyisophthalates. The coordination properties of hydroxyisophthalic acids were studied from the topological point of view, and a comparative topological analysis of coordination and H-bonded networks was performed. Structural correlations revealed in this study could be useful for the design of hydroxyisophthalate-based coordination networks, including porous metal-organic frameworks, proton conductors, and NLO materials.

Pb6O5(NO3)2: A Nonlinear Optical Oxynitrate Structurally Based on Lead Oxide Framework.

A high second harmonic generation response is demonstrated by a Pb6O5(NO3)2 lead oxynitrate whose identity was verified upon reinvestigation of the PbO-Pb(NO3)2 system. Its crystal structure exhibits a unique cationic [Pb6O5]2+ framework hosting orientationally ordered NO3- triangles in the channels. Easy preparation and high thermal stability (until ∼500 °C in air) suggest it to be a new promising NLO material.

Bridging the Salt-Inclusion and Open-Framework Structures: The Case of Acentric Ag4B4O7X2 (X = Br, I) Borate Halides.

An acentric borate family, Ag4B4O7X2 (X = Br, I), has been prepared by slow cooling stoichiometric melts in evacuated silica ampules. Their crystal structure is comprised of two porous interpenetrating frameworks and demonstrates a further development of the "salt-inclusion" architecture toward a "covalent-inclusion" structure. The (Ag2X)+ sublattice shows strong anharmonic vibrations. Thermal expansion is strongly anisotropic because of the presence of condensed rigid kernite boron-oxygen chains aligned perpendicular to the c axes.

Iodide-Iodates M3[IO3]12·Ag4I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response.

Single crystals of two new iodide-iodates, Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO3 umbrella-like groups and large Bi(Tb)-O polyhedra similar to those previously found in La3[IO3]12[IO3](Pb3O). Broad channels along the c-axis contain compensators: (Ag3I)2+ umbrella-like groups and additional Ag+ ions which form Ag44+ tetrahedral clusters augmented with I- halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE3[IO3]12[IO3](Pb3O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag3I)2+ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag4I]3+ polar clusters in the channels.

Complex Structural Behavior of BiMn7O12 Quadruple Perovskite.

Structural properties of a quadruple perovskite BiMn7O12 were investigated by laboratory and synchrotron X-ray powder diffraction between 10 and 650 K, single-crystal X-ray diffraction at room temperature, differential scanning calorimetry (DSC), second-harmonic generation, and first-principles calculations. Three structural transitions were found. Above T1 = 608 K, BiMn7O12 crystallizes in a parent cubic structure with space group Im3̅. Between 460 and 608 K, BiMn7O12 adopts a monoclinic symmetry with pseudo-orthorhombic metrics (denoted as I2/m(o)), and orbital order appears below T1. Below T2 = 460 K, BiMn7O12 is likely to exhibit a transition to space group Im. Finally, below about T3 = 290 K, a triclinic distortion takes place to space group P1. Structural analyses of BiMn7O12 are very challenging because of severe twinning in single crystals and anisotropic broadening and diffuse scattering in powder. First-principles calculations confirm that noncentrosymmetric structures are more stable than centrosymmetric ones. The energy difference between the Im and P1 models is very small, and this fact can explain why the Im to P1 transition is very gradual, and there are no DSC anomalies associated with this transition. The structural behavior of BiMn7O12 is in striking contrast with that of LaMn7O12 and could be caused by effects of the Bi3+ lone electron pair.

Syntheses, Crystal Structures, and Nonlinear Optical Activity of Cs2Ba[AnO2(C2H5COO)3]4 (An = U, Np, Pu) and Unprecedented Octanuclear Complex Units in KR2(H2O)8[UO2(C2H5COO)3]5 (R = Sr, Ba).

X-ray diffraction was applied to the elucidation of crystal structures of single crystals of Cs2Ba[AnO2(C2H5COO)3]4, where An = U(I), Np(II), Pu(III), and KR2(H2O)8[UO2(C2H5COO)3]5, where R = Sr(IV), Ba (polymorphs V-a and V-b). FTIR spectra were analyzed for the uranium-containing crystals I, IV, and V-b. Isostructural cubic crystals I-III are constructed of typical mononuclear anionic complex units [AnO2(C2H5COO)3]- and charge-balancing Cs and Ba cations. Features of actinide contraction in the six U-Np-Pu isostructural series known to date are analyzed. In crystal structures of IV and V two typical complexes [UO2(C2H5COO)3]- bind with a hydrated Sr or Ba cation to form the rare trinuclear neutral complex unit {R(H2O)4[UO2(C2H5COO)3]2}, where R = Sr, Ba. Two such trinuclear units and one typical mononuclear unit further bind with a K cation to form the unprecedented octanuclear neutral complex unit K[UO2(C2H5COO)3]{R(H2O)4[UO2(C2H5COO)3]2}2. As the derived polynuclear complexes of uranyl ion with carboxylate ligands in the crystal structures of IV and V are not the first but are rare examples, the equilibrium between mono and polynuclear complex units in aqueous solutions is discussed. The two polymorphic modifications V-a and V-b were studied at 100 K and at room temperature, respectively. Peculiarities of noncovalent interactions in crystal structures of the two polymorphs are revealed using Voronoi-Dirichlet tessellation. The nonlinear optical activity of noncentrosymmetric crystals I was estimated by its ability for second harmonic generation.

New iodate fluoride Rb2Ce(IO3)5F with nonlinear optical properties.

New noncentrosymmetric cerium(IV) iodate fluoride Rb2Ce(IO3)5F was prepared employing a hydrothermal technique. The compound crystallizes in the Cmc21 space group (#36) with cell parameters a = 11.1518(6) Å, b = 8.1187(4) Å and c = 17.1581(10) Å. The crystal structure of Rb2Ce(IO3)5F consists of layers composed of 8-vertex CeO7F and 7-vertex Rb(1)O7 and Rb(2)O6F polyhedra interconnected by I(2)O3 groups. These layers are stitched by trigonal pyramidal I(1)O3 and I(3)O3 groups into a 3D framework. Synthesized iodate fluoride is thermally stable in air up to 430 °C. According to DFT calculations, Rb2Ce(IO3)5F is a direct-gap semiconductor with a band gap of ca. 2.33 eV. This value is in good agreement with an estimated optical gap value of 2.35 eV. The important feature of Rb2Ce(IO3)5F is the ability to generate a second optical harmonic signal comparable to that of KH2PO4.

Sr9In(VO4)7 as a model ferroelectric in the structural family of ß-Ca3(PO4)2-type phosphates and vanadates.

Sr9In(VO4)7 was prepared by a solid-state method at 1270 K in air. This vanadate has the ß-Ca3(PO4)2-type structure and crystallizes in polar space group R3c. The structural parameters of Sr9In(VO4)7 were refined by the Rietveld method from laboratory powder X-ray diffraction data (XRD): the lattice parameters are a = 11.18016(9) Å and c = 39.6170(3) Å with Z = 6. In3+ cations occupy the octahedral M5 site, Sr2+ cations occupy the M1, M2, and M3 sites of the ß-Ca3(PO4)2-type structure, and the M4 site remains vacant. Sr9In(VO4)7 was characterized by differential thermal analysis (DTA), optical second-harmonic generation (SHG), high-temperature XRD, and dielectric measurements. All these methods prove the existence of a ferroelectric-paraelectric phase transition at T c = 974 K. This transition is compared with a similar transition in Ca9In(PO4)7 with lower T c = 902 K. The polar-to-centrosymmetric phase transition in such compounds has a quite unique mechanism of the order-disorder type. The structural transition involves slight shifts of the M1, M2, M3 cations and the E2O4, E3O4 tetrahedra, while half of the E1O4 tetrahedra (E = P or V) statistically reverse their orientation along the three-fold axis, so that the centre of symmetry appears in the structure as a whole. To invert the E1O4 tetrahedron, one oxygen anion should pass a large neighbouring cation (Sr2+ or Ca2+) that is only possible when intense rotational vibrations of the tetrahedra are excited at high temperatures. The lower Curie temperature in Ca9In(PO4)7 corresponds to the smaller rotational vibration amplitude of the P1O4 tetrahedron required to reverse this tetrahedra at T c in comparison with V1O4 in Sr9In(VO4)7.

Rb9-xAg3+xSc2(WO4)9: a new glaserite-related structure type, rubidium disorder, ionic conductivity.

A new triple tungstate Rb9-xAg3+xSc2(WO4)9 (0 ≤ x ≤ 0.15) synthesized by solid state reactions and spontaneous crystallization from melts presents a new structure type related to those of Cs7Na5Yb2(MoO4)9 and Na13Sr2Ta2(PO4)9. The title compound in centrosymmetric space group Cmcm contains dimers of two ScO6 octahedra sharing corners with three bridging WO4 tetrahedra. Three pairs of opposite terminal WO4 tetrahedra are additionally linked by AgO2 dumbbells to form {Ag3[Sc2(WO4)9]}9- groups, which together with some rubidium ions are packed in pseudohexagonal glaserite-like layers parallel to (001), but stacking of the layers is different in these three structures. In the title structure, the layers stack with a shift along the b axis and their interlayer space contains disordered Rb+ cations partially substituted by Ag+ ions. Almost linear chains of incompletely filled close Rb3a-Rb3d positions (the shortest distances Rb-Rb are 0.46 to 0.64 Å) are found to locate approximately along the b axis. This positional disorder and the presence of wide common quadrangular faces of Rb2 and Rb3a-Rb3d coordination polyhedra favor two-dimensional ionic conductivity in the (001) plane with Rb+ and Ag+ carriers, which was confirmed with bond valence sum (BVS) maps. Electrical conductivity measurements on Rb9Ag3Sc2(WO4)9 ceramics revealed a first-order superionic phase transition at 570 K with a sharp increase in the electrical conductivity. The conductivity σi = 1.8 × 10-3 S cm-1 at 690 K is comparable with the value of 1.0 × 10-3 S cm-1 (500 K) observed earlier for rubidium-ion transport in pyrochlore-like ferroelectric RbNbWO6.

New triple molybdate Rb2AgIn(MoO4)3: synthesis, framework crystal structure and ion-transport behaviour.

A new triple molybdate, Rb2Ag1+3xIn1-x(MoO4)3 (0 ≤ x ≤ 0.02), was found in the course of a study of the system Rb2MoO4-Ag2MoO4-In2(MoO4)3 and was synthesized as both powders and single crystals by solid-state reactions and spontaneous crystallization from melts. The structure of Rb2Ag1+3xIn1-x(MoO4)3 (x ≉ 0.004) is of a new type crystallizing in the centrosymmetric space group R-3c [a = 10.3982 (9), c = 38.858 (4) Å, Z = 12 and R = 0.0225] and contains (In,Ag)O6 octahedra and distorted Ag1O6 trigonal prisms linked by common faces to form [Ag(In,Ag)O9] dimers connected to each other via MoO4 tetrahedra into an open three-dimensional (3D) framework. Between two adjacent [Ag(In,Ag)O9] dimers along the c axis, an extra Ag2O6 trigonal prism with about 1% occupancy was found. The Ag1O6 and Ag2O6 prisms are located at levels of z ≉ 1/12, 1/4, 5/12, 7/12, 3/4 and 11/12, and can facilitate two-dimensional ionic conductivity. The 12-coordinate Rb atoms are in the framework cavities. The structure of Rb2AgIn(MoO4)3 is a member of the series of rhombohedral 3D framework molybdate structure types with a ≉ 9-10 Šand long c axes, which contain rods of face-shared filled and empty coordination polyhedra around threefold axes. Electrical conductivity of ceramics is measured by impedance spectroscopy. Rb2AgIn(MoO4)3 undergoes a `blurred' first-order phase transition at 535 K with increasing electrical conductivity up to 1.1 × 10-2 S cm-1 at 720 K. Thus, the compound may be of interest for developing new materials with high ionic conductivity at elevated temperatures.

Synthesis, crystal structures and properties of the new compounds K7-xAg1+x(XO4)4 (X = Mo, W).

Two new isostructural compounds, namely heptapotassium silver tetrakis(tetraoxomolybdate), K7-xAg1+x(MoO4)4 (0 ≤ x ≤ 0.4), and heptapotassium silver tetrakis(tetraoxotungstate), K7-xAg1+x(WO4)4 (0 ≤ x ≤ 0.4), have been synthesized and found to crystallize in the polar space group P63mc (Z = 2) with the unit-cell dimensions a = 12.4188 (2) and c = 7.4338 (2) Šfor K6.68Ag1.32(MoO4)4 (single-crystal data), and a = 12.4912 (5) and c = 7.4526 (3) Šfor K7Ag(WO4)4 (Rietveld analysis data). Both structures represent a new structure type, with characteristic [K1(XO4)6] `pinwheels' of K1O6 octahedra and six XO4 tetrahedra (X = Mo, W) connected by common opposite faces into columns along the c axes. The octahedral columns are linked to each other through Ag1O4 tetrahedra along with the K2 and K3/Ag2 polyhedra, forming the polar rods (...Ag1O4-X1O4-empty octahedron-Ag1O4...). Ag1 is located almost at the centre of the largest face of its coordination tetrahedron and seems to have some mobility. The new structure type is related to the Ba6Nd2Al4O15 and CaBaSiO4 types, and to other structures of the α-K2SO4-glaserite family. The differential scanning calorimetry (DSC) and second harmonic generation (SHG) results show that both compounds undergo first-order phase transformations to high-temperature centrosymmetric phases.

Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4: different filled derivatives of the cation-deficient Cs6Zn5(MoO4)8 structure.

Two new compounds, namely cubic tricaesium lithium dizinc tetrakis(tetraoxotungstate), Cs3LiZn2(WO4)4, and tetragonal trirubidium dilithium gallium tetrakis(tetraoxomolybdate), Rb3Li2Ga(MoO4)4, belong to the structural family of Cs6Zn5(MoO4)8 (space group I-43d, Z = 4), with a partially incomplete (Zn5/6□1/6) position. In Cs3LiZn2(WO4)4, this position is fully statistically occupied by (Zn2/3Li1/3), and in Rb3Li2Ga(MoO4)4, the 2Li + Ga atoms are completely ordered in two distinct sites of the space group I-42d (Z = 4). In the same way, the crystallographically equivalent A+ cations (A = Cs, Rb) in Cs6Zn5(MoO4)8, Cs3LiZn2(WO4)4 and isostructural A3LiZn2(MoO4)4 and Cs3LiCo2(MoO4)4 are divided into two sites in Rb3Li2Ga(MoO4)4, as in other isostructural A3Li2R(MoO4)4 compounds (AR = TlAl, RbAl, CsAl, CsGa, CsFe). In the title structures, the WO4 and (Zn,Li)O4 or LiO4, GaO4 and MoO4 tetrahedra share corners to form open three-dimensional frameworks with the caesium or rubidium ions occupying cuboctahedral cavities. The tetrahedral frameworks are related to that of mayenite 12CaO·7Al2O3 and isotypic compounds. Comparison of isostructural Cs3MZn2(MoO4)4 (M = Li, Na, Ag) and Cs6Zn5(MoO4)8 shows a decrease of the cubic lattice parameter and an increase in thermal stability with the filling of the vacancies by Li+ in the Zn position of the Cs6Zn5(MoO4)8 structure, while filling of the cation vacancies by larger Na+ or Ag+ ions plays a destabilizing role. The series A3Li2R(MoO4)4 shows second harmonic generation effects compatible with that of ß'-Gd2(MoO4)3 and may be considered as nonlinear optical materials with a modest nonlinearity.

BiScO3: centrosymmetric BiMnO3-type oxide.

With neutron powder diffraction, electron diffraction, and second-harmonic generation, we have shown that BiScO3 has a structure closely related to that of multiferroic BiMnO3, but BiScO3 crystallizes in the centrosymmetric space group of C2/c. These results bring up a question about the origin of ferroelectricity in BiMnO3. BiScO3 may serve as a model system to understand the role of Mn3+ ions in the ferroelectricity of BiMnO3.