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1.
Single crystals of two niobates, KBa2Nb5O15 and LaK2Nb5O15, were synthesized by high-temperature reaction and the crystal structures were determined by single crystal X-ray diffraction data. Although the space groups for these compounds were different (the non-centrosymmetrical space group P4bm (#100) for KBa2Nb5O15 and the centrosymmetrical one P4/mbm (#127) for LaK2Nb5O15), both compounds had the same tetragonal tungsten bronze-type (hereafter TTB-type) structure. The lattice parameters and R-factors of KBa2Nb5O15 (LaK2Nb5O15) were a = 12.533(2) (12.563(2)) and c = 4.0074(9) (3.9179(9)) Å, and R1 = 0.040 (0.047) and wR2=0.131 (0.120), respectively. From the crystal structural analysis, it was clarified that distribution of two large cations was different from each other in the way that K and Ba atoms in KBa2Nb5O15 were distributed statistically at two crystallographic sites and K and La atoms in LaK2Nb5O15 were ordered. 相似文献
2.
Hualong Song Xiangang Xu Xiaobo Hu Xiufeng Cheng Jiyang Wang Minhua Jiang 《Materials Research Bulletin》2005,40(4):643-649
Calcium barium niobate Ca0.28Ba0.72Nb2O6 (CBN-28) crystals were successfully grown by the Czochralski method. X-ray powder diffraction experiments indicated that CBN single crystals are tetragonal with a = 12.432(±0.002) Å and c = 3.957(±0.001) Å, which have almost the same structure as the Sr0.50Ba0.50Nb2O6 (SBN-50) crystal. The thermal expansion coefficient perpendicular to Z-direction had been measured to be 1.25 × 10−5 K−1 between 293.15 and 572.15 K, and along Z-axis was negative between 298.15 and 543.15 K. The specific heat of the crystal had been measured by the differential scanning calorimetric experiments. The transmittance spectra from 200 to 3200 nm were also measured. The measured temperature dependence of dielectric constants showed that the Curie temperature of the CBN-28 crystals is 260 °C, which is about 200 °C higher than that of the (SBN) crystal. 相似文献
3.
The crystal structure of Ca0.28Ba0.72Nb2O6 (CBN-28) crystal with Nd-doping has been determined from X-ray single crystal diffraction data, in the tetragonal system with space group P4bm and the following parameters: a = b = 12.458 Å, c = 3.954 Å, V = 613.688 Å3, and Z = 5. X-ray diffraction results on a Nd-doped CBN-28 single crystal also have demonstrated that Nd3+ and Ca2+ occupy the same site in the crystal structure. Dielectric and ferroelectric measurements have been performed. Transition from ferroelectric to paraelectric at around 223 °C has been observed. The Nd-doped crystal has a lower Curie temperature (Tm) than that of undoped CBN-28 crystal. The spontaneous polarization (Ps) and coercive electric field (Ec) also decrease compared with their values in the undoped CBN-28 crystal. 相似文献
4.
The crystal structures of two PbSb2O6-type compounds containing titanium, CdTi2O4(OH)2 and LaTiSbO6 were refined by X-ray powder diffraction data. For both compounds structure refinements with the space group were successful and the R-factors were RWP = 6.46% and RP = 4.90% for CdTi2O4(OH)2 and RWP = 9.55% and RP = 7.17% for LaTiSbO6. These crystal structures were the same as that of the typical PbSb2O6-type compound in spite of the existence of protons in the interlayer or two different metal ions in the layer. 相似文献
5.
Qingbiao Zhao 《Materials Research Bulletin》2011,46(2):166-169
Crystals of K2Hf2O5 and K4Hf5O12 were grown from molten potassium hydroxide flux. The crystal structures were determined by single-crystal X-ray diffraction. K2Hf2O5 crystallizes in the space group Pnna of the orthorhombic system, with unit cell dimensions of a = 5.780(1) Å, b = 10.640(2) Å, and c = 8.666(2) Å. This compound contains infinite chains of HfO6 octahedra that form a channel structure. K4Hf5O12 crystallizes in the space group of the trigonal system, with unit cell dimensions of a = 5.7877(2) Å and c = 10.3693(7) Å. This compound possesses a layered structure with six-coordinate Hf in three different coordination environments (trigonal prismatic, distorted octahedral, and regular octahedral). 相似文献
6.
The subsolidus phase equilibria of the Li2O-Ta2O5-B2O3, K2O-Ta2O5-B2O3 and Li2O-WO3-B2O3 systems have been investigated mainly by means of the powder X-ray diffraction method. Two ternary compounds, KTaB2O6 and K3Ta3B2O12 were confirmed in the system K2O-Ta2O5-B2O3. Crystal structure of compound KTaB2O6 has been refined from X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pmn21 (No. 31), with lattice parameters a = 7.3253(4) Å, b = 3.8402(2) Å, c = 9.3040(5) Å, z = 2 and Dcalc = 4.283 g/cm3. The powder second harmonic generation (SHG) coefficients of KTaB2O6 and K3Ta3B2O12 were five times and two times as large as that of KH2PO4 (KDP), respectively. 相似文献
7.
M ThirumalI.N Jawahar K.P SurendiranP Mohanan A.K Ganguli 《Materials Research Bulletin》2002,37(14):2321-2334
Oxides belonging to the families Ba3ZnTa2−xNbxO9 and Ba3MgTa2−xNbxO9 were synthesized by the solid state reaction route. Sintering temperatures of 1300°C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425°C hexagonally ordered structures were obtained for Ba3MgTa2−xNbxO9 over the entire range (0≤x≤1) of composition, while for Ba3ZnTa2−xNbxO9 the ordered structure exists in a limited range (0≤x≤0.5). The dielectric constant is close to 30 for the Ba3ZnTa2−xNbxO9 family of oxides while the Mg analogues have lower dielectric constant of ∼18 in the range 50 Hz to 500 kHz. At microwave frequencies (5-7 GHz) dielectric constant increases with increase in niobium concentration (22-26) for Ba3ZnTa2−xNbxO9; for Ba3MgTa2−xNbxO9 it varies between 12 and 14. The “Zn” compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the “Mg” analogues. 相似文献
8.
Crystals of RbPrHP3O10 have been grown by the flux technique and characterized by single-crystal X-ray diffraction. RbPrHP3O10 crystallizes in the triclinic space group with lattice parameters: a = 7.0655(5), b = 7.7791(4), c = 8.6828(6) Å, α = 74.074(3), β = 74.270(3), γ = 82.865(2)°, V = 441.09(5) Å3, Z = 2. The crystal structure has been solved yielding a final R(F2) = 0.0443 and Rw(F2) = 0.1426 for 1955 independent reflections (Fo2 ≥ 2σ(Fo2)). The structure of RbPrHP3O10 consists of PrO8 polyhedra and P3O105− groups sharing oxygen atoms to form a two-dimensional framework; the PrO8 polyhedra form infinite chains by edge-sharing. Each Rb+ ion is bonded to 10 oxygen atoms, these ions are located between chains formed of (HP3O10)4−. The energies of the vibrational modes of the crystal were obtained from measurements of the infrared spectrum. 相似文献
9.
Single crystals of a new niobium oxide, Cs3Fe0.44Nb5.56O16 were prepared at 1200°C under an Ar atmosphere. This compound has the orthorhombic space group Pbcm and Z=4. The lattice parameters were a=10.470(3), b=7.514(4) and c=21.312(3) Å, and the final R-factors were R=0.027 and Rw=0.033 for 1085 unique reflections. The crystal structure is a three-dimensional tunnel structure built up by edge- and corner-sharing NbO6 octahedra and (Fe,Nb)O4 tetrahedra and cesium atoms are located in two types of tunnels. The Cs+ ion in the tunnels was ion-exchanged partially with Rb+ ion. 相似文献
10.
N. Kumada T. Takei Y. Yonesaki N. Kinomura Y. Kameshima 《Materials Research Bulletin》2011,46(6):962-965
Single crystals of a new bismuth vanadate, Bi3.33(VO4)2O2 was prepared by hydrothermal reaction using a hydrated sodium bismuthate, NaBiO3·nH2O as one of the starting compounds. The crystal structure was determined by using single crystal X-ray diffraction data. This compound crystallizes in the triclinic space group (#2) with a = 7.114(1), b = 7.844(2), c = 9.372(2) Å, α = 106.090(7), β = 94.468(7) and γ = 112.506(8)°, Z = 2 and the final R factors are R1 = 0.052 and wR2 = 0.14 for 2085 unique reflections. The crystal structure is composed by four bismuth atoms with the coordination number of 6 or 8 and two VO4 tetrahedra, and one of four bismuth atoms is statistically distributed in the splitting sites with the distance of 0.83 Å. This compound exhibited photocatalytic behavior for decomposition of phenol under visible light irradiation and its activity was less than that of monoclinic BiVO4. 相似文献
11.
The ceramics with 0.90Pb(Zr0.50Ti0.50)O3-0.07Pb(Mn1/3Nb2/3)O3-0.03Pb(Ni1/2W1/2)O3 were prepared by adding Cr2O3. The effects of Cr2O3 doping on the phase structure, the microstructure and the electrical properties of ceramics were investigated. Meanwhile, the temperature stabilities of the resonant frequency (fr) and the electromechanical coupling factor (Kp) were studied. The results showed that the better temperature stability could be obtained at x = 0.2 wt.% when the calcining temperature was 800 °C and the sintering temperature was 1150 °C. The parameters were Δfr/fr25 °C = −0.17% and ΔKp/Kp25 °C = −1.39%. Moreover, the optimized electrical properties were also achieved, which were KP = 0.54, Qm = 1730, d33 = 330 pC/N, ?r = 2078 and tan δ = 0.0052. The optimized properties make the ceramics with this composition to be a good candidate for high power piezoelectric transformers applications. 相似文献
12.
Cu5Sb2O8SiO4 is orthorhombic, space group Pcca, with a = 19.031 (2), b = 9.3944 (6), c = 9.602 (2) Å, and z = 8. Its crystal structure was determined using single crystal X-ray diffraction (R1 = 0.0432 and wR2 = 0.1146). The compound presents a parwelite-like structure. Its anionic three-dimensional framework is built up of corner-sharing SbO6 octahedra and SiO4 tetrahedra, delimiting interconnected channels wherein Cu2+ with different coordination modes, are located. The χM and χMT product versus T plots, showed the Cu5Sb2O8SiO4 material to exhibit an anti-ferromagnetic character with a Neel temperature of about 27 K. 相似文献
13.
Toru Okada 《Materials Research Bulletin》2010,45(10):1443-9624
Glasses with the compositions of xLi2O-(70 − x)Nb2O5-30P2O5, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li+ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li+ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li2O content, and the glass of 60Li2O-10Nb2O5-30P2O5 shows the value of σ = 2.35 × 10−6 S/cm at room temperature and the activation energy (Ea) of 0.48 eV for Li+ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li3PO4 and NbPO5 are formed in the crystallization of the glasses and the crystallization results in the decrease in Li+ ion conductivity in all samples, indicating that any high Li+ ion conducting crystalline phases have not been formed in the present glasses. 60Li2O-10Nb2O5-30P2O5 glass shows a bulk nanocrystallization (Li3PO4 nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10−7 S/cm at room temperature and Ea = 0.49 eV. 相似文献
14.
The crystal structure of Pb3BiV3O12 was solved using single-crystal X-ray diffraction technique. The compound crystallizes in the cubic system (No. 220) with eulytite structure with a = 10.7490(7) Å, V = 1241.95(14) Å3 and Z = 4. The final R1 value of 0.0198 (wR2=0.0384) was achieved for 359 independent reflections during the structure refinement. The Pb2+ and Bi3+ cations occupy the special position (16c) while the oxygen anions occupy the general position (48e) in the crystal structure. Unlike many other eulytite compounds, all the crystallographic positions are fully occupied. The structure consists of edge-shared Pb/Bi octahedra linked at the corners to independent [VO4]3− tetrahedra units, generating a eulytite-type network in the crystal lattice. 相似文献
15.
Jasmine N. Millican Satoru Nakatsuji Yo Machida Julia Y. Chan 《Materials Research Bulletin》2007,42(5):928-934
Single crystals of R2Ir2O7 (R = Pr, Eu) have been synthesized using molten KF at 1373 K. The pyrochlore compounds crystallize in a cubic space group (No. 227, origin choice 2), with Z = 8. At room temperature, the lattice parameters are a = 10.3940(4) Å, V = 1122.92(7) Å3 and a = 10.274(3) Å, V = 1084.5(6) Å3 for Pr2Ir2O7 and Eu2Ir2O7, respectively. In this paper, we report the crystal growth of R2Ir2O7 (R = Pr, Eu) and their structure determinations from single crystal X-ray diffraction experiments at temperatures of 110, 115, and 298 K. 相似文献
16.
Volker Kahlenberg 《Materials Research Bulletin》2002,37(4):715-726
Sr10Al6O19 is monoclinic, space group C12/c1, a=34.5823(21) Å, b=7.8460(6) Å, c=15.7485(9) Å, β=103.68(1)°, V=4151.9(7) Å3, Z=8. The structure has been solved from a single crystal diffraction dataset by direct methods and subsequently refined by a full-matrix least-squares process to a residual index of R(|F|)=0.038 for 2537 observed reflections with I>2σ(I). The compound is an oligoaluminate containing highly puckered [Al6O19]-groups of corner-sharing tetrahedra; it is the first purely aluminate cluster of this type, but it resembles the [□6O19]-group recently found in α-Sr10□6O19. Linkage between the hexamers is provided by 11 crystallographically different strontium atoms located in planes parallel (1 0 0). They are coordinated by six-eight next oxygen neighbours. The structure can be derived from perovskite, ABO3, by introducing ordered vacancies into the substructure of the oxygen atoms. The A-sites in Sr10Al6O19 are exclusively occupied by Sr atoms, whereas strontium and aluminum atoms reside on the B-positions in the ratio 1:3. The relationship with perovskite can be expressed in the crystal chemical formula Sr(Al3/4Sr1/4)(O19/8□5/8). 相似文献
17.
Karima Horchani Mokhtar FeridJean-Claude Gacon Sylvain LecocqMalika Trabelsi-Ayedi Ivan Gregora 《Materials Research Bulletin》2002,37(7):1259-1267
Crystals of KDyP4O12 have been grown by the flux technique and characterized by single-crystal X-ray diffraction. KDyP4O12 crystallizes in the monoclinic C2/c space group with lattice parameters: a=7.8158(3), b=12.3401(5), c=10.4382(3) Å, β=111.053°(2), V=939.6(4) Å3, Z=4. The crystal structure has been refined yielding a final R(F2)=0.034 and Rw(F2)=0.082 for 902 independent reflections (Fo2≥2σ(Fo2)). The structure of KDyP4O12 consists of DyO8 polyhedra and cyclotetraphosphate P4O12 groups sharing oxygen atoms to form a three-dimensional framework, delimiting intersecting tunnels in which the potassium ion is located. Each K+ ion is bonded to 10 oxygen atoms. The energies of the vibrational modes of the crystal were obtained from measurements of the infrared and Raman spectra. 相似文献
18.
Alexander A. Tsirlin Roman V. Shpanchenko Evgeny V. Antipov 《Materials Research Bulletin》2005,40(5):800-809
The new complex vanadium oxide K2SrV3O9 has been synthesized and investigated by means of X-ray powder diffraction (XPD), electron microscopy and magnetic susceptibility measurements. The oxide has an orthorhombic unit cell with lattice parameters a = 10.1922(2) Å, b = 5.4171(1) Å, c = 16.1425(3) Å, space group Pnma and Z = 4. The crystal structure of K2SrV3O9 has been refined by Rietveld method using X-ray powder diffraction data. The structure contains infinite chains built by V4+O5 square pyramids linked to each other via VO4 tetrahedra. The chains form layers and potassium and strontium cations orderly occupy structural interstices between these layers. Electron diffraction as well as high resolution electron microscopy confirmed the structure solution. Magnetic susceptibility measurements revealed an antiferromagnetic interaction with J of the order of 100 K inside the chains and no long-range magnetic order above 2 K. The origin of the magnetic exchange is likely a result of super-exchange interaction through the two VO4 tetrahedra linking the polyhedra with the magnetic V4+ cations. 相似文献
19.
(5 − x)BaO-xMgO-2Nb2O5 (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO3, MgO, and Nb2O5 was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)5Nb4O15 was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg1/3Nb2/3)O3 was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?r = 36.69, Qf = 20,097 GHz, and τf = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?r = 39.2, Qf = 43,878 GHz, and τf = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb2O5 ceramics for applications in microwave dielectric resonators. 相似文献
20.
Mamata Tripathy 《Materials Research Bulletin》2007,42(5):950-960
We investigated isomorphous substitution of several metal atoms in the Aurivillius structures, Bi5TiNbWO15 and Bi4Ti3O12, in an effort to understand structure-property correlations. Our investigations have led to the synthesis of new derivatives, Bi4LnTiMWO15 (Ln = La, Pr; M = Nb, Ta), as well as Bi4PbNb2WO15 and Bi3LaPbNb2WO15, that largely retain the Aurivillius (n = 1) + (n = 2) intergrowth structure of the parent oxide Bi5TiNbWO15, but characteristically tend toward a centrosymmetric/tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2TiIV → MV + FeIII in Bi4Ti3O12, yields new Aurivillius phases, Bi4Ti3−2xNbxFexO12 (x = 0.25, 0.50) and Bi4Ti3−2xTaxFexO12 (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi4Ti3O12. Two new members of this family, Bi2Sr2Nb2RuO12 and Bi2SrNaNb2RuO12 that are analogous to Bi2Sr2Nb2TiO12, possessing tetragonal (I4/mmm) Aurivillius structure have also been synthesized. 相似文献