Accurate thermochronologic interpretation of zircon (U-Th)/He dates requires a realistic and practically useful understanding of He diffusion kinetics in natural zircon, ideally across the range of ...variation that characterize typically dated specimens. Here we present a series of date and diffusion measurements that document the importance of alpha dose, which we interpret to be correlated with accumulated radiation damage, on He diffusivity. This effect is manifest in both date-effective uranium (eU) correlations among zircon grains from single hand samples and in diffusion experiments on pairs of crystallographically oriented slabs of zircon with alpha doses ranging from ~10... to 10... α/g. We interpret these results as due to two contrasting effects of radiation damage in zircon, both of which have much larger effects on He diffusivity and thermal sensitivity of the zircon (U-Th)/He system than crystallographic anisotropy. Between 1.2 x 10... α/g and 1.4 x 10... α/g, the frequency factor, D0, measured in the c-axis parallel direction decreases by roughly four orders of magnitude, causing He diffusivity to decrease dramatically (for example by three orders of magnitude at temperatures between 140 and 220 ...C). Above ~2 x 10... α/g, however, activation energy decreases by a factor of roughly two, and diffusivity increases by about nine orders of magnitude by 8.2 x 10... α/g. We interpret these two trends with a model that describes the increasing tortuosity of diffusion pathways with progressive damage accumulation, which in turn causes decreases in He diffusivity at low damage. At high damage, increasing diffusivity results from damage zone interconnection and consequential shrinking of the effective diffusion domain size. Our model predicts that the bulk zircon (U-Th)/He closure temperature (Tc) increases from about 140 to 220 ...C between alpha doses of 10... to 10... α/g, followed by a dramatic decrease in Tc above this dose. Linking this parameterization to one describing damage annealing as a function of time and temperature, we can model the coevolution of damage, He diffusivity, and (U-Th)/He date of zircon. This model generates positive or negative date-eU correlations depending on the extent of damage in each grain and the date-eU sample's time-temperature history. (ProQuest: ... denotes formulae/symbols omitted.)
The new compounds
M
2+
Zr(SeO
4
)
3
(
M
2+
= Mg, Mn, Co, Ni, Zn, Cd) and Li
2
Zr(
X
O
4
)
3
(
X
= S, Se) were synthesized at 220 °C by reaction of Zr
2
O
2
(CO
3
)(OH)
2
with hydroxides or ...carbonates of
M
/ Li and the respective acids H
2
SeO
4
/H
2
SO
4
. They form crystals up to several tenths of a mm and were investigated by single crystal X-ray diffraction. The framework structures of these selenates can be deduced from that of monoclinic Fe
2
(SO
4
)
3
in space group
P
2
1
/n
, which is characterized by two types of isolated Fe
3+
O
6
octahedra, corner-linked with three different sulfate groups: ferric iron is substituted in 1:1 ratio by Zr
4+
and
M
2+
as already known for isotypic
M
Zr(SO
4
)
3
representatives. In the case of Li
2
Zr(
X
O
4
)
3
members, one additional lithium atom occupies a tetrahedral vacancy of the Fe
2
(SO
4
)
3
architecture.
Graphical abstract
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Recently, we have discovered a new class of amino acids salts containing different amino acids. In the present paper, we report crystal structures of three isostructural salts:
l
-argininium( +) ...sarcosine chloride (I),
l
-argininium( +) sarcosine bromide (II), and
l
-argininium( +) sarcosine iodide (III), formed by slow evaporation at room temperature from aqueous solutions containing stoichiometric ratios of components. The compounds crystallize in the polar space group
P
2
1
with two formula units in the asymmetric unit. The structures are stabilized due to N–H···O and N–H···X (X = Cl, Br, I) hydrogen bonds. Infrared spectra of all three crystals are shown and discussed.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Recently, we have discovered a new class of salts containing different amino acids. In the present paper, we report crystal structures of four types (A(1)HA(2)HY, A(1)HA(2)H···A(2)Y, ...A(1)HA(1)H···A(2)Y and A(1)H···A(2)
2
Y) of salts containing a hexafluorosilicate anion (Y is SiF
6
2−
) and amino acids glycine, sarcosine, dimethylglycine, betaine,
β
-alanine, and
l
-proline: (
β
-AlaH)(BetH)SiF
6
·H
2
O (I), (
β
-AlaH)(
l
-ProH)SiF
6
(II), (
β
-AlaH)(
l
-ProH···
l
-Pro)SiF
6
(III), (BetH)(BetH···Sar)SiF
6
·H
2
O (IV), (GlyH···DMG)
2
SiF
6
(V), and (DMGH···Sar)
2
SiF
6
(VI). The O⋅⋅⋅O distances in dimeric cations (
l
-ProH···
l
-Pro), (BetH···Sar), (GlyH···DMG), and (DMGH···Sar) are 2.439 (3), 2.5310 (12), 2.4979 (9), and 2.4612 (19) Å in (III), (IV), (V), and (VI), respectively.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Tetrahedrite compounds Cu(12-x)Mn(x)Sb4S13 (0 ≤x≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6Mn1.4Sb4S13 was performed by single crystal X-ray ...diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I4combining macron3m) of a tetrahedrite. The large atomic displacement parameter of the Cu2 atoms was described by splitting the 12e site into a partially and randomly occupied 24g site (Cu22) in addition to the regular 12e site (Cu21), suggesting a mix of dynamic and static off-plane Cu2 atom disorder. Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn(2+) at the Cu(1+) site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit ZT decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum ZT = 0.76 at 623 K is obtained for Cu12Sb4S13. The coefficient of thermal expansion 13.5 ± 0.1 × 10(-6) K(-1) is obtained in the temperature range from 460 K to 670 K for Cu10.2Mn1.8Sb4S13. The Debye temperature, Θ(D) = 244 K for Cu10.2Mn1.8Sb4S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μB/f.u. for Cu10.2Mn1.8Sb4S13 is fairly consistent with a high spin 3d(5) ground state of Mn.
Zr
2
(OH)
2
(
X
O
4
)
3
·4H
2
O (
X
= S, Se), Zr(SO
4
)
2
·4H
2
O, and Zr(SeO
3
)
2
were synthesized at low-hydrothermal conditions from mixtures of Zr
2
O
2
(CO
3
)(OH)
2
, the respective acids, ...and minor amounts of water. While Zr
2
(OH)
2
(
X
O
4
)
3
·4H
2
O (
X
= S, Se) and Zr(SO
4
)
2
·4H
2
O form crystals up to several tenths of a mm, Zr(SeO
3
)
2
was mainly obtained as microcrystalline powder, single crystals rarely exceeded 10 μm in size. Samples were investigated by single-crystal X-ray techniques and in the case of Zr(SeO
3
)
2
also by X-ray powder diffraction. The compounds Zr
2
(OH)
2
(
X
O
4
)
3
·4H
2
O (
X
= S, Se) crystallize in the Ce
2
(OH)
2
(SO
4
)
3
·4H
2
O structure type (
C
2
/c
,
Z
= 4,
a
= 13.034(2) / 13.308(3),
b
= 6.500(1) / 6.683(2),
c
= 15.056(3) / 15.383(4) Å,
β
= 96.27(1) / 96.81(1)°,
V
= 1267.9(4) / 1358.5(6) Å
3
for
X
= S / Se, respectively). Tetragonal aniprisms Zr
8
O
8
are edge-connected to dimers that share corners with
X
O
4
tetrahedra forming a three-dimensional network. Zr(SO
4
)
2
·4H
2
O (
Fddd
,
Z
= 8,
a
= 5.498(1),
b
= 11.618(3),
c
= 25.893(6) Å,
V
= 1653.9(6) Å
3
) is isotypic with the respective selenate compound. Occasionally, pseudomerohedral twinning is observed, simulating a larger monoclinic
C
-centered unit cell. Again, tetragonal antiprisms Zr
8
O
8
are formed; however, they are corner-linked with SO
4
tetrahedra to Zr(SO
4
)
2
layers interconnected solely by hydrogen bonds. Zr(SeO
3
)
2
crystallizes in
P
2
1
/
c
, Z = 2;
a
= 4.9724(3),
b
= 8.5992(5),
c
= 6.9447(3) Å,
β
= 110.128(3)°,
V
= 278.81(3) Å
3
(unit cell from powder data) and belongs to the β-Sn(SeO
3
)
2
structure type established further for Ti(SeO
3
)
2
and Pb(SeO
3
)
2
. Isolated ZrO
6
octahedra share corners with the selenite groups forming a three-dimensional network.
Graphical abstract
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Intermetallic type-I clathrates continue to attract attention as promising thermoelectric materials. Here we present structural and thermoelectric properties of single crystalline Ba
8
(Cu,Ga,Ge, )
...46
, where denotes a vacancy. By single crystal X-ray diffraction on crystals without Ga we find clear evidence for the presence of vacancies at the 6c site in the structure. With increasing Ga content, vacancies are successively filled. This increases the charge carrier mobility strongly, even within a small range of Ga substitution, leading to reduced electrical resistivity and enhanced thermoelectric performance. The largest figure of merit
ZT
= 0.9 at 900 K is found for a single crystal of approximate composition Ba
8
Cu
4.6
Ga
1.0
Ge
40.4
. This value, that may further increase at higher temperatures, is one of the largest to date found in transition metal element-based clathrates.
Vacancy filling by Ga substitution enhances the TE performance of type-I clathrates
via
improving charge carrier mobility.
The continuous deposition of hazardous metalliferous wastes derived from industrial steelmaking processes will lead to space shortages while valuable raw metals are being depleted. Currently, these ...landfilled waste products pose a rich resource for microbial thermoacidophilic bioleaching processes. Six thermoacidophilic archaea (
, and
) were cultivated on metal waste product derived from a steelmaking process to assess microbial proliferation and bioleaching potential. While all six strains were capable of growth and bioleaching of different elements,
outperformed other strains and its bioleaching potential was further studied in detail. The ability of
cells to break down and solubilize the mineral matrix of the metal waste product was observed
scanning and transmission electron microscopy. Refinement of bioleaching operation parameters shows that changes in pH influence the solubilization of certain elements, which might be considered for element-specific solubilization processes. Slight temperature shifts did not influence the release of metals from the metal waste product, but an increase in dust load in the bioreactors leads to increased element solubilization. The formation of gypsum crystals in course of
cultivation on dust was observed and clarified using single-crystal X-ray diffraction analysis. The results obtained from this study highlight the importance of thermoacidophilic archaea for future small-scale as well as large-scale bioleaching operations and metal recycling processes in regard to circular economies and waste management. A thorough understanding of the bioleaching performance of thermoacidophilic archaea facilitates further environmental biotechnological advancements.
1‐(3‐Halopropyl)‐1H‐tetrazoles and their corresponding FeII spin‐crossover complexes have been investigated in a combined experimental and theoretical study. Halogen substitution was found to ...positively influence the spin transition, shifting the transition temperature about 70 K towards room temperature. Halogens located at the ω position were found to be too far away from the coordinating tetrazole moiety to have an electronic impact on the spin transition. The subtle variation of the steric demand of the ligand in a highly comparable series was found to have a comparatively large impact on the spin‐transition behavior, which highlights the sensitivity of the effect to subtle structural changes.
Steric fine‐tuning: 1‐(3‐Halopropyl)‐1H‐tetrazoles and their corresponding FeII spin‐crossover complexes have been investigated in a combined experimental and theoretical study. Halogen substitution of 1‐(propyl)‐1H‐tetrazole has been found to shift the spin‐transition temperature by about 70 K towards room temperature (see figure). The reason for this impact was found to lie in the steric fine‐tuning of the ligand backbone.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
