Charge Compensation in Trivalent Doped Ca3(SiO4)Cl2

2015 ◽  
Vol 1744 ◽  
pp. 113-118 ◽  
Author(s):  
M. R. Gilbert
Keyword(s):  
Charge Compensation ◽  
Monovalent Cation ◽  
Ionic Radii ◽  
Substitution Process ◽  
Solution Energy ◽  
Site Selectivity ◽  
Trivalent Cations ◽  
Charge Balancing ◽  
Pyrochemical Reprocessing ◽  
Static Lattice

ABSTRACTCalcium chlorosilicate (Ca3(SiO4)Cl2) is seen as a potential host phase for the immobilization of Cl-rich wastes arising from pyrochemical reprocessing, a waste stream often containing a mix of both di- and trivalent cations. Substitution of trivalent cations into the lattice requires some form of charge compensation to ensure the lattice remains charge neutral overall. Whilst previous work has only examined this through the formation of Ca vacancies, this study investigates the feasibility of charge-balancing via the substitution of a monovalent cation onto the Ca sites of the lattice. To that end, a series of static lattice calculations were performed to determine the site selectivity of monovalent cations of differing size when substituted onto the Ca sites of the calcium chlorosilicate lattice and the solution energies for the overall substitution processes compared with those for charge compensation via vacancy formation. In all cases the monovalent charge-balancing species shows a clear preference for substitution onto the Ca1 site in the calcium chlorosilicate lattice. The solution energy of the substitution process increases with the increasing ionic radii of both the mono- and trivalent species as the steric stresses associated with substitution of larger cations than the Ca2+ host increase. As such, only charge-balancing using Li+, Na+ or K+ is more favourable than via formation of a Ca vacancy.

Effect of Charge-balancing Species on Sm3+ Incorporation in Calcium Vanadinite

2015 ◽  
Vol 1744 ◽  
pp. 119-124
Author(s):  
M. R. Gilbert
Keyword(s):  
Experimental Approach ◽  
Secondary Phase ◽  
Monovalent Cation ◽  
Phase System ◽  
Secondary Phases ◽  
Good Potential ◽  
Phase Systems ◽  
Multi Phase ◽  
Charge Balancing ◽  
Static Lattice

ABSTRACTApatites are often seen as good potential candidates for the immobilization of halide-rich wastes. In particular, phosphate apatites have received much attention in recent years, however, their synthesis often produces complicated multi-phase systems, with a number of secondary phases forming [1.2]. Calcium vanadinite (Ca5(VO4)3Cl) demonstrates a much simpler phase system, with only a single Ca2V2O7 secondary phase which can easily be retarded by the addition of excess CaCl2. However, when doping with SmCl3 (as an inactive analogue for AnCl3) the Sm forms a wakefieldite (SmVO4) phase rather than being immobilized within the vanadinite, a result of having to form an energetically unfavourable Ca vacancy in order for the lattice to remain neutral overall. It has been postulated that charge-balancing the lattice via co-substitution of a monovalent cation will be less disfavoured and therefore help stabilise formation of a (Ca5-2xSmxAx)(VO4)3Cl solid solution (A = monovalent cation). This has been investigated using a combined modelling and experimental approach. Static lattice calculations performed using Li+, Na+ and K+ as charge-balancing species have shown the energy cost to be less than half that of charge-balancing via formation of a Ca vacancy. As a result, solid state synthesis of (Ca5-2xSmxLix)(VO4)3Cl, (Ca5−2xSmxNax)(VO4)3Cl and (Ca5-2xSmxKx)(VO4)3Cl solid solutions have been trialled, and analysis of the resulting products has shown a significant reduction in both the SmVO4 and Ca2V2O7 secondary phases across all dopant levels.

Synthesis and Characterization of Brannerite Compositions for MOX Residue Disposal

MRS Advances ◽  
2016 ◽  
Vol 2 (10) ◽  
pp. 557-562 ◽  
Author(s):  
D.J. Bailey ◽  
M.C. Stennett ◽  
N.C. Hyatt
Keyword(s):  
Powder Diffraction ◽  
Microstructural Analysis ◽  
Charge Compensation ◽  
Phase Assemblage ◽  
Secondary Phases ◽  
Host Matrix ◽  
Neutron Absorber ◽  
X Ray ◽  
Valence States ◽  
Trivalent Cations

ABSTRACTDue to their high actinide content MOX residues require immobilization within a robust host matrix. Although it is possible to immobilize actinides in vitreous wasteforms; ceramic phases, such as brannerite (UTi2O6), are attractive due to their high waste loading capacity and relative insolubility. Brannerites Gd0.1U0.9Ti2O6, Ce0.1U0.9Ti2O6and Gd0.1U0.81Ce0.09Ti2O6were prepared using an oxide route. Charge compensation of trivalent cations was expected to occur via the oxidation of U (IV) to higher valence states (U (V) or U (VI)). Gd was added to act as a neutron absorber in the final Pu bearing wasteform and Ce was used as a structural surrogate for Pu. X-ray absorption spectroscopy showed that Ce (IV) was reduced to Ce (III) in all cases. X-ray powder diffraction of synthesized specimens found that the final phase assemblage was strongly affected by processing atmosphere (air or argon). Prototypical brannerite was formed in all compositions, secondary phases observed were found to vary according to processing atmosphere and stoichiometry. Microstructural analysis (SEM) of the sintered samples confirmed the results of the X-ray powder diffraction.

scholarly journals CERTAIN EFFECTS OF SALTS ON THE PENETRATION OF BRILLIANT CRESYL BLUE INTO NITELLA

1927 ◽  
Vol 10 (3) ◽  
pp. 425-436 ◽  
Author(s):  
Marian Irwin
Keyword(s):  
Ph Value ◽  
Monovalent Cation ◽  
Borate Buffer ◽  
Brilliant Cresyl Blue ◽  
Rate Of Penetration ◽  
Basic Dye ◽  
Cresyl Blue ◽  
Inhibiting Effect ◽  
Buffer Mixture ◽  
Trivalent Cations

The effect of various substances on living cells may be advantageously studied by exposing them to such substances and observing their subsequent behavior in solutions of a basic dye, brilliant cresyl blue. The rate of penetration of the basic dye, brilliant cresyl blue, is decreased when cells are exposed to salts with monovalent cations before they are placed in the dye solution (made up with borate buffer mixture). This inhibiting effect is assumed to be due to the effect of the salts on the protoplasm. This effect is not readily reversible when cells are transferred to distilled water, but it is removed by salts with bivalent or trivalent cations. In some cases it disappears in dye made up with phosphate buffer mixture, or with borate buffer mixture at the pH value in which the borax predominates, and in the case of NaCl it disappears in dye containing NaCl. No inhibiting effect is seen when cells are exposed to NaCl solution containing MgCl2 before they are placed in the dye solution. The rate of penetration of dye is not decreased when cells are previously exposed to salts with bivalent and trivalent cations. The rate is slightly increased when cells are placed in the dye solution containing a salt with monovalent cation and probably with bivalent or trivalent cations. In the case of the bivalent and trivalent salts the increase is so slight that it may be negligible.

Defects in orthorhombic LaMnO3 – ionic versus electronic compensation

2018 ◽  
Vol 20 (28) ◽  
pp. 19257-19267 ◽  
Author(s):  
Ailbhe L. Gavin ◽  
Graeme W. Watson
Keyword(s):  
Alkaline Earth ◽  
Charge Compensation ◽  
Compensation Mechanism ◽  
Site Selectivity ◽  
Electronic Compensation ◽  
Comprehensive Study

The findings of this work represent a comprehensive study of alkaline earth doping of bulk orthorhombic LaMnO3 to determine site selectivity and the charge compensation mechanism for the dopants.

Structure determination of KScS2, RbScS2and KLnS2(Ln = Nd, Sm, Tb, Dy, Ho, Er, Tm and Yb) and crystal–chemical discussion

2015 ◽  
Vol 71 (7) ◽  
pp. 623-630 ◽  
Author(s):  
Lubomír Havlák ◽  
Jan Fábry ◽  
Margarida Henriques ◽  
Michal Dušek
Keyword(s):  
Rare Earth ◽  
Structure Determination ◽  
Structure Type ◽  
Trivalent Cation ◽  
Crystal Chemical ◽  
Ionic Radii ◽  
Structural Family ◽  
Trivalent Cations ◽  
Ytterbium Sulfide

The title structures of KScS2(potassium scandium sulfide), RbScS2(rubidium scandium sulfide) and KLnS2[Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS2, RbScS2and KTbS2) or redetermined. All of them belong to the α-NaFeO2structure type in agreement with the ratio of the ionic radiir3+/r+. KScS2, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared arec,aandc/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinatesz(S2−) and the bond-valence sums.

scholarly journals Low-temperature infrared spectrum and atomic-scale structure of hydrous defects in diopside

2020 ◽  
Vol 32 (5) ◽  
pp. 505-520
Author(s):  
Etienne Balan ◽  
Lorenzo Paulatto ◽  
Jia Liu ◽  
Jannick Ingrin
Keyword(s):  
Low Temperature ◽  
Infrared Spectra ◽  
Density Functional ◽  
Charge Compensation ◽  
Atomic Scale ◽  
Absorption Bands ◽  
Major Mechanism ◽  
Bearing Defects ◽  
The Density Functional Theory ◽  
Trivalent Cations

Abstract. Hydrous defects in diopside (CaMgSi2O6) play an important role in the water budget of the Earth's mantle. Related OH-stretching modes lead to a variety of infrared absorption bands observed in natural or experimental samples. In the present study, we report new low-temperature infrared spectra of reference natural diopside samples in the OH-stretching range. In parallel, the structure and vibrational properties of a series of OH-bearing defects in diopside are theoretically determined at the density functional theory level. The infrared spectra make it possible to resolve additional bands in the region above 3600 cm−1 and reveal that their anharmonic behavior differs from that of the bands at lower frequency. A comparison of theoretical results with experimental data makes it possible to propose atomic-scale geometries corresponding to observed OH-stretching bands. It confirms that the bands observed at 3620–3651 cm−1 are related to M3+ ions substituted for Si in tetrahedral sites, while the 3420 cm−1 band is associated with the Na+ for Ca2+ substitution. In both cases, H+ incorporation compensates the charge deficit due to the heterovalent substitution. The other major mechanism of water incorporation in diopside relates to the charge compensation of cationic vacancies, among which Ca vacancies play a central role. The 3357 cm−1 band corresponds to doubly protonated Ca vacancies in pure diopside. In experimental diopside-bearing trivalent cations, the bands at 3432–3460 cm−1 correspond to singly protonated Ca vacancies with a nearby octahedral M3+ ion, while the 3310 cm−1 band likely involves a more remote charge compensation by M3+ ions. More complex defects associating Ca vacancies with tetrahedral M3+ and octahedral Ti4+ ions are proposed for the bands observed between 3500 and 3600 cm−1 in natural diopside. The Fe2+ for Mg2+ and Fe2+ for Ca2+ substitutions are also found to affect nearby OH-bearing defects, causing a shift and broadening of OH stretching bands in chemically more complex diopside samples.

scholarly journals Effects of Charge Compensation on the Thermoelectric Properties of (La1-zCez)0.8Fe4-xCoxSb12 Skutterudites

2021 ◽  
Vol 59 (4) ◽  
pp. 239-246
Author(s):  
Kyung-Wook Jang ◽  
Ye-Eun Cha ◽  
Deok-Yeong Choi ◽  
Sunuk Kim ◽  
Won-Seon Seo ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Properties ◽  
Secondary Phase ◽  
Negative Temperature ◽  
Charge Compensation ◽  
Filling Ratio ◽  
Ionic Radii ◽  
Co Substitution ◽  
The Matrix

La/Ce-partially double-filled and Co-charge-compensated (La<sub>1−z</sub>Ce<sub>z</sub>)<sub>0.8</sub>Fe<sub>4−x</sub>Co<sub>x</sub>Sb<sub>12</sub> skutterudites were synthesized, and their thermoelectric properties were studied by varying the filling ratio and charge compensation. X-ray diffraction analysis revealed that the matrix phase was skutterudite and a secondary phase was determined to the marcasite FeSb<sub>2</sub>. However, the formation of marcasite could be inhibited by increasing the Co content. Rare-earth antimonides, including LaSb<sub>2</sub> and CeSb<sub>2</sub>, which were formed in fully filled La<sub>1−z</sub>Ce<sub>z</sub>Fe<sub>4−x</sub>Co<sub>x</sub>Sb<sub>12</sub>, were not found after La/Ce partial filling. La/Ce filling and Co substitution were confirmed by the decrease in lattice constants, from 0.9137 to 0.9099 nm, with increasing Ce and Co contents. Electrical conductivity showed negative temperature dependence, indicating metallic or degenerate semiconductor characteristics. Intrinsic conduction resulted in the maximum Seebeck coefficient at temperatures between 723 and 823 K. As the Co-substitution and Ce-filling contents increased, the Seebeck coefficient increased, while electrical and thermal conductivities decreased. This was considered to be due to difference in the valences of La<sup>3+</sup> and Ce<sup>3+/4+</sup> and the increase in carrier concentration caused by Co charge compensation. However, because they had similar atomic masses and ionic radii, the effects of the La/Ce filling ratio were not significant. Instead, Co charge compensation had the dominant effect on thermoelectric properties. The maximum Seebeck coefficient of 165.4 µVK<sup>-1</sup> was obtained for (La<sub>0.25</sub>Ce<sub>0.75</sub>)<sub>0.8</sub>Fe<sub>3</sub>CoSb<sub>12</sub> at 823 K, and the highest electrical conductivity of 2.27 × 10<sup>5</sup> S m<sup>-1</sup> was achieved for (La<sub>0.75</sub>Ce<sub>0.25</sub>)<sub>0.8</sub>Fe<sub>4</sub>Sb<sub>12</sub>. (La<sub>0.25</sub>Ce<sub>0.75</sub>)<sub>0.8</sub>Fe<sub>3</sub>CoSb<sub>12</sub> exhibited the lowest thermal conductivity of 2.15 W m<sup>-1</sup>K<sup>-1</sup> at 523 K and (La<sub>0.75</sub>Ce<sub>0.25</sub>)<sub>0.8</sub>Fe<sub>3.5</sub>Co<sub>0.5</sub>Sb<sub>12</sub> showed the highest power factor of 2.53 mW m<sup>-1</sup> K<sup>-2</sup> at 723 K. The maximum dimensionless figure of merit, ZT<sub>max</sub> = 0.71, was achieved at 723 K for (La<sub>0.75</sub>Ce<sub>0.25</sub>)<sub>0.8</sub>Fe<sub>3</sub>CoSb<sub>12</sub>.

Sign in / Sign up

Export Citation Format

Share Document