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Materials Research Bulletin, 2013
Recently, researchers are focussing on the mixed metal oxide materials which are widely used in multifunctional devices such as multiferroics and spintronics. In this perspective, ABO 3 based compounds are widely investigated because of their potential applications in various cutting edge technologies [1-5]. Generally, ABO 3 compounds exhibit different crystal structures such as perovskite, ilmenite, corundum and LiNbO 3 structure which is differentiated according to their cations ionic radii, cationic arrangement, coordination number and synthetic parameter (e.g., pressure and temperature) [6]. In ABO 3 perovskite structure, A-site cation (A = Alkaline earth metal, alkaline metals and rare earth metals) in 12-fold coordination is surrounded by eight BO 6 octahedrons and B-site cation (transition metals) is coordinated by six oxygen anions and it forms BO 6 octahedron [7]. In ilmenite, corundum and LiNbO 3 structures are similar through 6-fold coordination in A and B-site cation but it can be classified under their cation arrangements. In ilmenite structure, cation arrangement along the c-axis is A-B-Vac-B-A-Vac-A-B.. . (Vac = Vacancy) and similar cation arrangement also occur along the plane perpendicular to the c-axis. In corundum type structure cations are randomly arranged. In LiNbO 3 structure, cation arrangement along the c-axis is A-B-Vac-A-B-Vac-A-B.. . [8,9]. NiTiO 3 belongs to the ilmenite type structure with both Ni and Ti possessing octahedral coordination and the alternating cation layers occupied by Ni 2+ and Ti 4+ alone [10]. NiTiO 3 is an n-type semiconducting material whose band gap value is 2.12 eV, possess high electrical resistivity and high permittivity. Owing to its superior properties they are widely used in the application of sensors, photo catalyst, memory storage devices and microwave dielectric properties etc [11-13]. Survey on the reports of NiTiO 3 tells that these materials possess semiconducting and antiferromagnetic behaviour. Among them, Heller et al. [14] studied the magnetic properties of NiTiO 3 and found the antiferromagnetic nature at 23 K. Boysen and Lerch [15] reported that NiTiO 3 undergoes a second order phase transition from ilmenite structure with space group R3 to corundum structure with space group R3c at T c = 1570 K which is due to Ni and Ti order-disorder transition. Singh et al. [11] reported the activation energy of single crystal NiTiO 3 is 1.06 eV. Fennie [16] has been reported that high pressure LiNbO 3 phase of FeTiO 3 and NiTiO 3 exhibit the multiferroics nature. NiTiO 3 particles and thin films have been synthesized by different methods such as solution combustion [17], polymeric precursor [18], sol-gel spin coating [19], sol-gel [20,21], modified pechini [22], flux [11], stearic acid gel [23], co-precipitation [24]
Ab initio determination and Rietveld refinement of the crystal structure of Ni0.50TiO(PO4)
Powder Diffraction, 1999
The structure of the oxyphosphate Ni0.50TiO(PO4) has been determined ab initio from conventional X-ray powder diffraction data by the “heavy atom” method. The cell is monoclinic (space group P21/c, Z=4) with a=7.3830(5) Å, b=7.3226(5) Å, c=7.3444(5) Å, and β=120.233(6)°. Refinement of 46 parameters by the Rietveld method, using 645 reflexions, leads to cRwp=0.152, cRp=0.120, and RB=0.043. The structure of Ni0.50TiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing TiO6 octahedra running parallel to the c axis, crosslinked by phosphate tetrahedra and in which one-half of octahedral cavities created are occupied by Ni atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.231) and short (1.703 Å) Ti–O bonds along chains.
Journal of Alloys and Compounds, 2018
In this study, we investigated the changes of the structural and optical properties of NiTiO materials modified by transition metal doping. Cobalt (Co) or tungsten (W)-doped NiTiO 3 materials were successfully prepared by a modified Pechini method via solvothermal treatment. Raman, FTIR, and XRD spectroscopic analyses showed that the Co 2+ ions were selectively doped into Ni 2+ sites in the NiTiO 3 lattice while maintaining an ilmenite structure, resulting in a solid solution of triple transition metal oxides. The size similarity between Co and Ni induced the formation of a solid solution, Co x Ni 1-x TiO 3 , in the ilmenite structure. In contrast, W doping into the NiTiO 3 ilmenite structure resulted in an irregularity of the materials due to the characteristics of the heavy transition metal dopant. Along with increasing the W content, the crystallite size in the ilmenite structure decreased from 90.2 to 74.5 nm and new Raman bands at 831 and 892 cm-1 for WO x appeared at high W contents. However, the PL emission intensities gradually decreased with increasing doping content, implying that the recombination process was inhibited in the NiTiO 3 materials by the dopants.
Structural characterization of NiTiO 3 nanopowders prepared by stearic acid gel method
Pure nickel titanate nanopowders were successfully prepared in wet-chemistry synthesis method, using nickel stearate and tetra-n-butyl titanate as Ni, Ti sources and stearic acid as complexing reagent. The gel was calcined at different temperatures in air ranging from 500 to 750 °C. Results of thermal analysis are given, including both DTG and TG. Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the crystallization process, the particle size and morphology of the calcined powders. The results indicated that nickel titanate nanopowders with particle size between 30 and 65 nm could be obtained after calcinations of the dried gel at 750 °C for 2 h.
Thermogravimetric study on preparation of NiTiO 3 in different reaction times
The thermodynamic properties of the fabrication of NiTiO 3 material in different reaction times are reported. The design of this material is accessible through a new efficient sol–gel methods, utilizing Ni(Ac) 2 Á4H 2 O and Ti(O i Pr) 4 as starting materials for the formation of NiTiO 3 final product through thermal decomposition. The ther-mogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to analyze the reaction of Ni(Ac) 2 Á4H 2 O and Ti(O i Pr) 4 , which produces precursor materials at 0.5, 1, 2, 24, 48 and 72 h of reaction times, as well as the thermal stability of these precursors and the final product. The DSC data show an exothermic phenomenon of releasing large amount of energy of-1393 J/g at T Peak 655 K due to the first event of decomposition started at T Onset 607 K and finished at T Endset 663 K for the precursor materials obtained at 0.5 h of reaction, showing the presence of starting materials in this precursor. A similar exothermic behavior was observed in the sample of 1 h of reaction time and was vanished in the materials obtained at 2–72 h of reaction, indicating the influence of the time on the completion of reaction and formation of NiTiO 3 crystalline phase as final product of thermal decomposition. In addition, using the information obtained from the TG/DSC, XRD and FTIR analyses, the optimum temperature for the thermal decomposition of the precursor materials to NiTiO 3 with fairly high crystallinity was also determined and discussed.
Crystal Structure and Properties of Nd4Co3O10+δ and Nd4Ni3O10−δ
Journal of Solid State Chemistry, 2000
The crystal structures of Nd 4 M 3 O 10 (M ؍ Co, Ni) correspond to the n ؍ 3 members of the Ruddlesden+Popper series of A n؉1 B n O 3n؉1 . Rietveld-type analyses of high-resolution powder synchrotron X-ray and powder neutron di4raction (PND) data of Nd 4 Co 3 O 10؉ and Nd 4 Ni 3 O 10؊ reveal their crystal structures to be slightly monoclinically distorted. The symmetry lowering to space group P2 1 /a is caused by tilting of the MO 6 octahedra within the (NdMO 3 ) 3 layers. Long apical M+O distances are observed in the octahedra pointing toward the NdO layers. Magnetic susceptibility data for Nd 4 Co 3 O 10.00 indicate longrange antiferromagnetic ordering below 15 K. The ordered moment is too low to be detected by PND at 8 K. Above 60 K, two nearly Curie+Weiss paramagnetic regions are observed: 60+560 K and 650+920 K. Thermal analysis data for Nd 4 Co 3 O 10؉ in atmospheres of oxygen and nitrogen shows a complex behavior, with respect to both possible phase transitions and redox properties.
2018
Nanostructured As2Ni3O8 samples were synthesized via facile solid-state reactions at 850 and 950 °C for 8h using As2O3, Ni(CH3COO)2.2H2O and Ni(NO3)2.6H2O raw materials. The synthesized nanomaterials were characterized by powder X-ray diffraction (PXRD) technique and fourier-transform infrared (FTIR) spectroscopy. The rietveld analyses showed that the obtained materials were crystallized well in monoclinic crystal structure with the space group P121/c1. The lattice parameters of the targets were about a = 5.76 Å, b = 9.54 Å and c = 10.18 Å with β = 92.95 °. It was found that nickel nitrate created a highly crystalline and pure As2Ni3O8 structure. However, nickel acetate created the target with lower purity and crystal phase growth; it produced the samples with smaller crystallite sizes. Reaction temperature changing showed that the parameter affected on the crystal growth of the obtained materials. The morphologies of the synthesized materials were studied by field emission scanning...
Quantitative determination of the crystal structure of Ni4Ti3 precipitates
Materials Science and Engineering: A, 2006
The structure of Ni 4 Ti 3 , which occurs as a precipitate in Ni-rich NiTi, has already been determined of having the R-3 space group. This was done using basic electron diffraction by Tadaki et al. also providing an approximation of the atomic coordinates. In the present work a least squares refinement method based on quantitative electron diffraction is used to optimise the structure of the Ni 4 Ti 3 unit cell. This method, in combination with Density Functional Theory (DFT) calculations, results in a structure for which the composition and R-3 space group of the Tadaki model is maintained but the atom positions are clearly shuffled. The R-factor (similar to the one used in X-ray diffraction refinement) drops from 12.5% for the original Tadaki structure to 8.2% for the newly refined one, and moreover the change of atomic coordinates explains in a better manner the shrinking of the Ni 4 Ti 3 unit cell in reference to the NiTi matrix.