ABSTRACT
[This corrects the article DOI: 10.1016/j.heliyon.2019.e01628.].
ABSTRACT
Defect pyrochlore oxide powders ABi2Ta5O16, in the pseudo-binary systems BiTaO4-ATa3O8 (A = Na, Tl), were prepared by solid state method. The structural study showed that all oxides crystallize in a cubic system with the space group Fd3m, the lattice parameter "a" were determined using Rietveld refinement method. For systematic study on densification from powders, the samples were pressed with a uniaxial pressure into pellets; sintering temperature, holding time and heating rate were optimized. Techniques, including X-ray diffraction, IR-Raman, MEB, dilatometry, were employed to investigate the structure and the morphology of the synthesized powders and sintered materials. The dielectric characteristics, relative permittivity and dielectric losses (tgδ), determined at room temperature are comparable to those of other pyrochlores.
ABSTRACT
In this paper, we report a synthesis of a new lacunar apatite, KCdPb3(PO4)3, using solid state method, and its application as modifier of carbon paste electrode (KLA-CPE) to determine mercury (II). Sodium replacement with potassium induced a linear variation of the crystallographic parameters a and c according to Vegard's law and led to amplify the electrical signal of the working electrode. The peak currents of mercury (II) increased linearly with their concentration at the range from 2.0×10(-7)molL(-1) to 1.0×10(-4)molL(-1) using differential pulse anodic stripping voltammetry. The detection limit was found to be 1.11×10(-8)molL(-1). The use of this electrochemical sensor has been successfully implemented for the determination of Hg (II) in seawater and fish samples. The obtained results were found to be very satisfactory.
ABSTRACT
In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1-xAsxO4 (0⩽x⩽1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x=0.7 and x=0.8. Furthermore, increasing temperature for the compositions (0.8⩽x⩽1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x=0.7 and 0.8.
ABSTRACT
Synthesis of apatites, Na1-xKxCaPb3(PO4)3 0 ⩽ x ⩽ 1, with anion vacancy were carried out using solid state reactions. The solid solution of apatite-type structure crystallize in the hexagonal system, space group P63/m (No. 176). Rietveld refinements showed that around 90% of Pb(2+) cations are located in the (6h) sites, the left amount of Pb(2+) cations are located in the (4f) sites; 27-31% of Ca(2+) cations are located in the (6h) sites, the left amount of Ca(2+) cations are located in the (4f) sites. The ninefold coordination sites (4f) are also occupied by the K(+) and Na(+) monovalent ions. The structure can be described as built up from [PO4](3-) tetrahedra and Pb(2+)/Ca(2+) of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [001]. These tunnels are connected by cations of mixed sites (4f) which are half occupied by Pb(2+)/Ca(2+) and half by Na(+)/K(+) mixed cations. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit cell group analysis and by comparison with other apatites. Vibrational spectra of all the compositions are similar and show some linear shifts of the frequencies as a function of the composition toward lower values due the substitutions of Na(+) by K(+) with a larger radius.
Subject(s)
Apatites/chemistry , Spectrum Analysis, Raman , Vibration , Cations , Crystallography, X-Ray , Lead/chemistry , Potassium/chemistry , Powders , Spectrophotometry, InfraredABSTRACT
Raman spectra of a series of orthophosphates M(0.50)TiO(PO(4)) (M=Mg, Zn, Ni, Co, Fe, and Cu) have been recorded in crystalline state. Factor group analysis has been performed for space group P2(1)/c and assignments of the internal modes of the [PO(4)] tetrahedra and [TiO(6)] octahedra have been made.
