Hexagonal Lattice Parameters Research Articles

Microstructural investigation of Cu2+ doped nanohydroxyapatites

Pure and Cu2+ doped nanohydroxyapatites were synthesised by a precipitation method to investigate the effect of Cu2+ ions on the structure of hydroxyapatite (HA) and its thermal stability after the air sintering at 1100°C. A small amount of CaO was observed in the Cu2+ doped HAs after the X-ray diffraction results. The addition of Cu2+ changed the hexagonal lattice parameters of the HA and resulted in smaller grain size after sintering at 1100°C. The addition of Cu2+ ions into HA resulted in smaller grain sizes (between 282 and 248 nm).

Synthesis and properties of colored copper-containing alkaline-earth phosphates with an apatite structure

Colored compounds A5(PO4)3Cu0.1OHz, where A = Ba1-xSrx (x=0,0.5,0.8), Sr1-y Cay (y=0,0.2, 0.5, 1), and Ba1/3Sr1/3Ca1/3 with an apatite structure containing copper ions in the hexagonal channels have been synthesized by the thermal treatment of the corresponding carbonates, oxides, and ammonium hydrophosphate at 1150°C. The use of the composition with A = Ba0.5Ca0.5 gives a multiphase product containing apatite (Ba1-xCax)5(PO4)3CuyOHz with x ∼ 0.2 as the major phase. The hexagonal lattice parameters of apatite depend linearly on the content of solid solution in the alkaline-earth metals. In the series of A = Ba, Ba-Sr, Sr, Sr-Ca, and Ca, the color of the samples changes smoothly from blue through violet to pink, whereas the samples with A = Ba0.5Ca0.5 and Ba1-3Sr1-3Ca1-3 are light gray. The diffuse reflectance electronic spectra exhibit two absorption bands characteristic of the copper ions in the hexagonal channels. Their positions depend on the alkaline-earth metal content of the compound. The third characteristic band appears in the spectrum of calcium apatite. Its relative intensity increases when calcium is gradually replaced by strontium and especially by barium, which results in worsening and even loss of the sample color. These spectral changes are presumably due to the transition of some copper ions from the hexagonal channels to other positions of the crystal lattice.

Understanding the hcp anisotropy in Cd and Zn: the role of electron correlation in determining the potential energy surface

Cadmium crystallises in the hcp structure, but with an anomalously large c/a ratio, indicating a strong distortion away from ideal packing. Coupled cluster calculations within the framework of the method of increments with an embedding scheme for metals were performed to explore the potential energy surface of cadmium with respect to the hexagonal lattice parameters. This potential energy surface is compared to density functional theory based surfaces, as calculated with various functionals. The overall flatness of the potential energy surface over a wide range of values of the lattice parameter c is analogous for both treatments, however only within the method of increments do we quantitatively describe the cohesion. The overall behaviour of the method of increments for cadmium is consistent with previous results for zinc, emphasising the dominant role of electronic correlation in achieving a sufficiently accurate description of bonding properties for the two elements; however, a detailed analysis shows differences. We discuss this in detail in terms of the correlation contributions of the s- and d-electrons.

Crystal Structure Of Magnesium Iridoboride, MglrB

BIrMg, hexagonal, P6222 (no. 180), a = 5.2752(7) A, c = 9.439(2) A, V = 227.5 A, Z = 6, Rgt(F) = 0.017, wRref(F) = 0.019, T = 295 K. Source of material The MgIrB compound was prepared using powders of Mg (99.8 %), Ir (99.9%) and crystalline B (99.999%) as startingmaterials. The elements mixture was ground, pressed into pellets, embedded in Ta ampoules and sealed under argon. The annealing was performed at 1293 K for 14 days and at 1333 K for 15 days with intermediate re-grinding. Experimental details The single phase samplewas obtained from the samplewith nominal composition Mg1.1IrB1.1. The X-ray powder diffraction patternwas indexedwith a hexagonal unit cell and lattice parameters a = 5.2736(3)A and c = 9.4358(7)A.When changing initial mixture compostition to Mg0.96IrB0.94 a slight lattice parameters reduction to a = 5.2702(2) A, c = 9.429(1) A was observed. The largest lattice parameters (cf. Abstract) were found for theMgIrB single crystal obtained from the sample with nominal composition Mg1.38IrB1.46 by annealing at 1273 K for 18 days. Analogously to the Mg RhB 1.x phase [1] we assume a small homogeneity range for Mg IrB 1.x with the minimum x close to 0 observed in the single crystal used for the structure determination. The Flack parameter value of 0.0 reveals correctness of the absolute structure. Discussion The synthesis of numerous ternary magnesium rhodium borides [1-4] initiated us to study the Mg-Ir-B system with iridium as the electron analogue of rhodiumwith the aim to investigate the platinummetal nature influence on the crystal structure and chemical bonding of ternary borides. The crystal structure of MgIrB is similar to Mg RhB 1.x [1]. It can be described as a framework of the distorted trigonal prisms [BIr4(Mg2)2], sharing the bases and side edges. The distorted hexagonal channels of the framework directed along c axis are occupied by Mg1 atoms. Each boron atom forms a short distance of 1.87(1) A to the next boron atom and, in addition, short distances of 2.203(3) and 2.210(7)A to the next iridium atoms. On this way a 2D [IrB] network is formed. In Mg RhB 1.x [1] the 2D [RhB] network was shown to be anionic. In analogy, we suppose the same character for 2D [IrB]. For theMg RhB 1.x compound the vacancies inMg1 site were experimentally observed and then interpreted using the results of chemical bonding analysis. The single crystal diffraction data for theMgIrB show the full occupation of theMg1 positions (99.8(2) %) and yield the composition MgIrB (x = 0). It agrees with the maximum lattice parameters found for the single crystal data. Z. Kristallogr. NCS 224 (2009) 17-18 / DOI 10.1524/ncrs.2009.0010 17 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: black prism, size 0.050 × 0.020 × 0.020 mm Wavelength: Mo K0 radiation (0.7107 A) %: 930.5 cm Diffractometer, scan mode: Rigaku AFC7, )/2 2max: 63.01° N(hkl)measured, N(hkl)unique: 2830, 244 Criterion for Iobs, N(hkl)gt: Iobs > 2 !(Iobs), 227 N(param)refined: 15 Programs: WinCSD [5], ATOMS [6], SHELXS-97 [7] Table 1. Data collection and handling. B 6j 0.602(2) 2x$1 1⁄2 0.006(2) Table 2. Atomic coordinates and displacement parameters (in A). Atom Site x y z Uiso

A new Kondo antiferromagnet Ce(Ni0.25In1.75)

We find that Ce(Ni0.25In1.75) crystallizes inthe hexagonal AlB2-type structurewith lattice parameters a = 0.4850(5) nm and c = 0.3908(5) nm. Magnetic susceptibility, electrical resistivity and low-temperaturespecific heat data reveal that the bulk phase transition at3.7 ± 0.2 Kin Ce(Ni0.25In1.75) is to an antiferromagnetic state. The magnetic contribution to the resistivityρmag ofCe(Ni0.25In1.75) increasesas ln(T) when temperature is lowered from room temperature and reaches a plateau at9 K, followed by a rapid decrease around 4 K. These results associated witha reduction of the Ce magnetic moment and of the magnetic entropy atTN suggestthat Ce(Ni0.25In1.75) could be a Kondo antiferromagnet. The Kondo temperature is estimated to be of order 6 K.

Multiple Minima on the Energy Landscape of Elemental Zinc: A Wave Function BasedAb InitioStudy

Zinc crystallizes in the hcp structure, but with an anomalously large c/a ratio, indicating a strong distortion away from ideal packing. Coupled cluster calculations within the framework of the method of increments, improved by an embedding scheme for metals, were performed to explore the potential energy surface of zinc with respect to the hexagonal lattice parameters. The inclusion of the filled d shell in the correlation treatment proved to be essential. From the exceptional shape of the potential energy surface the existence of a zinc modification with a nearly ideal c/a ratio can be deduced.

Preparation of Aluminum Oxynitride by Nitridation of a Precursor Derived from Aluminum–Glycine Gel and the Effects of the Presence of Europium

Spinel‐type AlON, Al2.75□0.25O3.74N0.26, was obtained by ammonia nitridation of an oxide precursor prepared by peptizing a glycine gel with aluminum nitrate. To achieve crystallization, the nitrided product had to be annealed at 1500°C for 10 min in flowing nitrogen. The use of glycine instead of citric acid was important for obtaining a white product without residual carbon. A similar preparation method was used for adding small amounts of europium below 10 mol%. A strong blue emission was observed for products ranging from 0.5 to 3.0 mol% Eu doping. The product with 0.5 mol% doping had a maximum emission intensity at 400 nm for an excitation of 254 nm. The products with 1 and 3 mol% doping showed double maxima at 475 and 520 nm. These three emissions were due to the presence of divalent europium in the EuAl12O19 magnetoplumbite‐like aluminum oxynitride impurity mixed with the AlON spinel major phase. The 1 mol% Eu‐doped product exhibited expanded hexagonal lattice parameters (a=0.5591 and c=2.236 nm) compared with the values for EuAl12O19 magnetoplumbite itself, observed in the 7.7 mol%‐doped product without any strong emission. The above spectrum change was discussed in relation to the coordination around Eu2+.

Effect of AlF3, CaF2 and MgF2 on hot-pressed hydroxyapatite–nanophase alpha-alumina composites

Nanophase alpha-alumina and hydroxyapatite composites (with and without 5wt% AlF3, CaF2 or MgF2, added separately) were hot pressed at 1100°C and 1200°C to investigate their mechanical properties and phase stability. Hydroxyapatite slightly decomposed to tri-calcium-phosphate when there was no F− present. With the addition of AlF3, CaF2 or MgF2 into the composite, it improved its thermal stability and mechanical properties. Substitution of OH− by F− ions in hydroxyapatite was verified by the change in hydroxyapatite's hexagonal lattice parameters and unit cell volume. A fracture toughness of 2.8MPam and μ-hardness of 8.25GPa were calculated for the composite containing CaF2 after the hot pressing at 1200°C.

Effect of MgF2 on hot pressed hydroxylapatite and monoclinic zirconia composites

Hydroxylapatite (HA) has been widely used in biomedical applications because of its excellent biocompatibility in the human body. A total of 25 wt% monoclinic (m) zirconia–HA composites (with and without 5 wt% MgF2) were synthesized to investigate their mechanical properties and phase stability. In HA–m-ZrO2 composites, HA and m-ZrO2 reacted to form CaZrO3 when there was no F− present in the composite and m-ZrO2 partially transformed to tetragonal ZrO2. When MgF2 was added into the system, it improved the thermal stability of the phases, densification, hardness, and fracture toughness of the composites and it caused the m-ZrO2 to transform completely to t-ZrO2 by incorporating the Mg2+ ions present in MgF2 in the ZrO2. Moreover, the stability of HA was improved by incorporating the F− ions from MgF2 in place of OH− ions in HA. Substitution of OH− by F− ions was verified by the change in HA’s hexagonal lattice parameters. A fracture toughness of 2.0 MPa√m was calculated for the composite containing MgF2.

Effect of YF 3 on hot-pressed hydroxyapatite and monoclinic zirconia composites

Monoclinic zirconia and hydroxyapatite (HA) composites with or without 5 wt% YF 3 were synthesized to investigate their mechanical properties and phase stability. HA decomposed to tri-calcium-phosphate and CaZrO 3 in the 25 wt% ZrO 2–75 wt% HA composite. However, thermal stability of the phases, densification, hardness and fracture toughness were improved when 5 wt% YF 3 was added into the system. Five weight percent YF 3 increased the transformation of monoclinic-ZrO 2 into tetragonal/cubic-ZrO 2 by incorporating the Y 3+ ions present in YF 3 when the hot pressing temperature was increased from 1100 to 1200 °C. Moreover, the stability of HA was also improved by incorporating the F − ions from YF 3 in the place of OH − ions in HA. Substitution of OH − by F − ions was verified by the change in HA's hexagonal lattice parameters. A fracture toughness of 1.93 MPa√m was calculated for the same composite.

Synthesis and magnetic properties of Mn doped ZnO nanowires

Mn doped ZnO nanowires have been synthesized using a simple autocombustion method. The as-synthesized Mn doped ZnO nanowires were characterized by X-ray diffraction and transmission electron microscopy. An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Mn concentration. Optical absorption studies show an increment in the band gap with increasing Mn content, and also give evidence for the presence of Mn 2+ ions in tetrahedral sites. All Zn 1− x Mn x O ( 0 ≤ x ≤ 0.25 ) samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of the Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicate ferrimagnetic behavior. The origin of ferrimagnetism is likely to be either the intrinsic characteristics of the Mn doped samples, or due to some spinel-type impurity phases present in the samples that could not be detected.

Solid-State Chemistry and Electrochemistry of LiCo1 ∕ 3Ni1 ∕ 3Mn1 ∕ 3O2 for Advanced Lithium-Ion Batteries: III. Rechargeable Capacity and Cycleability

Reaction mechanism of was examined by ex situ X-ray diffraction (XRD) and electrochemical methods. According to XRD results, the change in hexagonal lattice parameters was quite similar to that of , i.e., the unit cell volume was almost constant at in , indicating homogeneous phase reaction over an entire range. Reversible-potential measurements on against a lithium electrode were also carried out and the solid-state redox reactions were described by applying the concept of electrochemical density of states (EDS). Gibbs free-energy change for the reaction of was obtained to be , which was slightly higher than that for . Rechargeable capacity as a function of charge-end voltage was examined for cells and the relation between in and in V was given to be . From these results, rechargeable capacity and cycleability as a function of charge-end voltage are discussed in relation to the reaction mechanism of .

Structural investigation of thin films of Ti 1− xAl xN ternary nitrides using Ti K-edge X-ray absorption fine structure

Thin films of Ti 1− x Al x N nitrides were prepared over a large range of composition (0 ≤ x < 1) on Si substrates using nitrogen reactive magnetron sputtering from composite metallic targets. Ti K-edge X-ray Absorption Spectroscopy experiments were carried for a better understanding of the local structure. The evolution of the intensity of Ti K-edge pre-edge peak gives evidence of the incorporation of Ti in hexagonal lattice of AlN for Al-rich films and in cubic lattice of TiN for Ti-rich films. An attempt to determine their atomic structure by combining X-ray diffraction and Ti K-edge Extended X-ray Absorption Fine Structure is presented. The evolution of the nearest neighbour and next-nearest neighbour distances depending on the composition is presented and discussed together the cubic and hexagonal lattice parameters. A possible contribution of amorphous nitrides is suggested.

Structure and electron density analysis of electrochemically and chemically delithiated LiCoO 2 single crystals

Single crystals of Li 0.68CoO 2, Li 0.48CoO 2, and Li 0.35CoO 2 were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO 2 single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the hexagonal lattice parameters a=2.8107(5) Å, c=14.2235(6) Å, and c/ a=5.060 for Li 0.68CoO 2; a=2.8090(15) Å, c=14.3890(17) Å, and c/ a=5.122 for Li 0.48CoO 2; and a=2.8070(12) Å, c=14.4359(14) Å, and c/ a=5.143 for Li 0.35CoO 2. The crystal structures were refined to the conventional values R=1.99% and w R=1.88% for Li 0.68CoO 2; R=2.40% and w R=2.58% for Li 0.48CoO 2; and R=2.63% and w R=2.56% for Li 0.35CoO 2. The oxygen–oxygen contact distance in the CoO 6 octahedron was determined to be shortened by the delithiation from 2.6180(9) Å in LiCoO 2 to 2.5385(15) Å in Li 0.35CoO 2. The electron density distributions of these Li x CoO 2 crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed.

Effect of ZrF 4 on hot-pressed hydroxyapatite/monoclinic zirconia composites

Composites of 25 wt.% monoclinic zirconia and 75 wt.% hydroxyapatite (HA) (with and without 5 wt.% ZrF4) were hot pressed to investigate their mechanical properties and phase stability. HA decomposed to tricalcium phosphate when there was no ZrF4 present. Addition of ZrF4 into the composite improved its thermal stability and mechanical properties. Substitution of OH− by F− ions was verified by the change in HA’s hexagonal lattice parameters. A fracture toughness of 2.1 MPa √m and microhardness of 6.9 GPa were calculated for the composite containing ZrF4.

Electronic Structure of Intercalation Compounds of CoxNbS2

Cobalt intercalation into niobium disulfide with layered structure is presented. Powder X-ray diffraction study reveals that single-phase CoxNbS2 forms in the compositional range of 0.15 ≤ x ≤ 0.55. The hexagonal lattice parameters a and c monotonically increase with cobalt content up to x ∼ 0.5, while a and c are constant and decreasing from x = 0.5 to 0.55, respectively. The temperature dependence of electric resistivity shows metallic behavior at 0.15 ≤ x < 0.49 whereas semiconducting behavior is seen at 0.49 ≤ x ≤ 0.55, so that metal−semiconductor transition occurs at the composition x = 0.49. The temperature dependence of magnetic susceptibility obeys a Curie−Weiss law in the whole compositional range, suggesting localized electronic behavior around Co ions. The valance state of Co in CoxNbS2 was evaluated as divalent from effective Bohr magneton. The ab initio computation based on density functional theory was performed for NbS2 and Co1/3NbS2. The dz2 band arising from the NbS6 trigonal-prism crysta...

Thermoreactivity of Sol-Gel Precursor for ZnO-Based Thin Films

The thermoreactivity of a zinc acetate non-alkoxide solution used for the preparation of ZnO-based thin films was investigated in the temperature range 20-600°C by TG-DTA, XRD and SEM data. We found that the formation in air of ZnO crystallites from the sol-gel precursor occurs above 150°C simultaneously with the decomposition of an intermediary compound, most probably carbonate hydroxide (sclarite and/or hydrozincite). At 200 °C, the crystalline structure is well defined in terms of ZnO hexagonal lattice parameters, although residual organic compounds and water were not yet fully removed and an amorphous phase coexists. A kinetic investigation on the thermal decomposition of sol-gel precursor from DTA data using Kissinger differential equation is also presented. Apparent activation energy values of about. 100 kJ mol-1 corresponding to the nonisothermal decomposition of solid precursors in the temperature range 170-250oC have been found.

Al3+ Doped Nano-Hydroxyapatites and their Sintering Characteristics

Pure and Al3+ doped nano-hydroxyapatites (HA) were synthesized by a precipitation method to investigate their densification and thermal stability after the air sintering at 1100°C and 1300°C. Second phases were formed after increasing the Al3+ content from 2.5% to 7.5% in HA and increasing the sintering temperature from 1100°C to 1300°C. Al3+ addition into HA resulted in change in the hexagonal lattice parameters from the pure HA. When the sintering temperature was increased from 1100°C to 1300°C, densification was improved, which was verified by SEM micrographs. Al3+ addition resulted in smaller grain size after the sintering at 1300°C.

Quantitative TEM analysis of a hexagonal mesoporous silicate structure

TEM analysis of mesoporous materials is generally undertaken to give qualitative results. Accurate quantitative analysis is demonstrated in this study. A systematic image analysis of a powder form of a hexagonal mesoporous material known as KIT-6 is conducted using a transmission electron microscope (TEM). Three types of image contrast typically appear in this material (a hexagonal honeycomb structure, wide and narrow parallel lines). The honeycomb face is used to characterise this material in terms of a conventional 2-D hexagonal structure and the d-spacings for the (100) and (110) planes are experimentally measured in varying focus conditions. A tilting experiment is conducted to determine how the angle of tilt affects the line spacing and their visibility. Tilting has very little effect on the line spacing, whereas it affects the visibility of both the wide and narrow lines by limiting an angle range of visibility. The hexagonal lattice structure parameter determined by TEM method is found to be approximately 7% lower than that calculated by low-angle X-ray diffraction. Thus we conclude that TEM data can be used to determine the geometry and dimensions of hexagonal mesoporous silica materials, with a small error in the hexagonal lattice parameter.

Thin ZnO films prepared by chemical solution deposition on glass and flexible conducting substrate

Thin films of zinc oxide (ZnO) are deposited by a simple method of successive immersion of substrate in (NH4)2ZnO2(0.1 M) chemical solution and in boiling water. Films of a thickness ≈ 500 nm could be deposited on stainless steel and glass by 40 immersions. The composition, structure, optical bandgap and the charge transport mechanism were determined and the results are presented. Films are stoichiometric and have the same hexagonal lattice parameters as for powder samples. Films are formed from grains with a mean size of a few 100 nm. Grains consist of crystallites of mean size 20–30 nm. For films deposited on stainless steel, the crystallites are highly oriented along their c-axis perpendicular to the substrate. Films have a high optical transparency (above 80%) in the visible region and bandgap energy in the range 3.38–3.42 eV. Films are intrinsically n-type and the charge transport across the films is controlled by a shallow trapping level in accordance with the Poole–Frenkel mechanism. The doubly-ionized trapping level has a concentration of 4×1011 cm-3 and zero-field ionization energy of 110 meV. Adsorption of oxygen by annealing the films in air yields a singly-ionized trap.