HF Systems Research Articles

Phase Stability Diagrams of Ti–M–O–C (M = Zr, Hf, Nb, and Ta) Systems at 1800 K

Phase stability diagrams of Ti–M–O–C (M = Zr, Hf, Nb, and Ta) systems at 1800 K were constructed as a function of the carbon activity, oxygen partial pressure, and solution formation characteristics, in order to determine the optimum conditions for the formation of (Ti0.75M0.25)C via carbothermal reduction of oxide mixtures. The tendency to form (Ti0.75M0.25)C was predicted on the basis of the standard Gibbs free energies of formation $$ (\Delta {\text{G}}_{f}^{^\circ } ) $$ of (Ti0.75M0.25)C solid-solution carbides, calculated by first-principles simulations. It was concluded that at 1800 K, the (Ti0.75Nb0.25)C and (Ti0.75Ta0.25)C phases are more stable than the TiC–NbC and TiC–TaC mixtures, whereas the (Ti0.75Zr0.25)C and (Ti0.75Hf0.25)C phases are less stable than the corresponding TiC–ZrC and TiC–HfC mixtures. The phase stability diagrams of the Ti–M–O–C systems were then drawn using the calculated $$ \Delta {\text{G}}_{f}^{^\circ } $$ values and used to predict the tendencies to form solid-solution phases. The validity of the theoretical predictions was then verified using experimental results.

Special Issue on Wastewater Treatment and Reuse Technologies

Wastewater treatment allows for the safe disposal of municipal and industrial wastewater to protect public health and the ecosystem[...]

Decoupled Hf and Nd isotopes in suspended particles and in the dissolved load of Late Archean seawater

Abstract It is generally agreed that decoupling of the Hf and Nd isotope systems in modern aqueous systems is a result of incongruent release of Hf during terrestrial weathering of the continental crust, although the mechanism(s) behind this process are not yet fully understood. We here present Hf–Nd isotope data for the Neoarchean Krivoy Rog Banded Iron Formation (BIFs), Ukraine, and combine observations on modern aqueous environments with those of the early Earth to further evaluate the mechanism(s) behind Hf–Nd isotope decoupling in aqueous systems. The pure Late Archean Krivoy Rog chemical sediment endmember, representing the dissolved pool of ancient seawater, shows decoupled eNd2.60Ga-eHf2.60Ga values of −2.3 and +9.48, respectively, and suggests that decoupled Hf–Nd isotopes had been a global rather than a local phenomenon in Neoarchean seawater. This further reveals that incongruent Hf release via terrestrial weathering and erosion of emerged and evolved continental landmasses were widespread geological processes by Late Archean time. Impure Krivoy Rog BIF samples, composed of a mixture of seawater-derived and detrital Nd and Hf, show systematically more positive eNd2.60Ga values, but still reveal decoupled eNd-eHf values relative to an associated schist that plots slightly below the “terrestrial array”. This suggests that mineral sorting between a zircon-bearing sand-sized fraction and fine-grained sediment particles occurred on/in Late Archean continents, rivers and oceans, and had significant impact on the chemical compositions of the suspended and dissolved element loads of Late Archean seawater. Less radiogenic Hf isotope compositions in the Krivoy Rog seawater relative to detritus-contaminated BIFs further suggest a pathway for high-temperature hydrothermal Hf into anoxic Archean seawater, that diluted the even more radiogenic Hf isotopic composition of continental run-off, created by the mineralogical composition of the continental hinterland and the “zircon effect”. Alternatively, the less pronounced decoupling of eHf-eNd in Late Archean seawater may be related to a shorter residence time of Hf relative to Nd. Furthermore, systematically more positive initial eNd values in detritus-contaminated Archean BIFs relative to respective dissolved seawater loads suggest that weathered and eroded material of (ultra)mafic rock suites had significant impact on the suspended and dissolved fractions in Archean seawater.

Generalized stacking fault energies and ideal strengths of MC systems (M = Ti, Zr, Hf) doped with Si/Al using first principles calculations

The IVB transition metal carbides, MC, (M = Ti, Zr and Hf, respectively) and the synthesis of M3(Si/Al)C2 have been extensively studied due to their excellent mechanical, thermal and electrical properties. In this work, the effects of solute atoms (Si/Al) on the deformation mechanism and ideal strengths in various MC (M = Ti, Zr, Hf) systems are investigated systematically using first principle calculations. The deformation mechanisms of MC may vary from the glide of perfect dislocation to twinning once Si/Al solute atom concentration (η) in the glide plane reaches some critical value, indicating that the stacking faults and twin structures may appear in the region with high solute concentration, such as grain boundary, which agrees with the experimental results. Compared with MC, the ideal tensile/shear strengths of M3(Si/Al)C2 decreases obviously, which can be attributed to weak M–(Si/Al) bonds in contrast to M–C bonds.

U–Pb SHRIMP II age and origin of zircon from lhertzolite of the bug Paleoarchean complex, Ukrainian Shield

Complex study of the U–Pb and Lu–Hf systems of zircon from a lhertzolite lens of Archean gneiss enderbites of the Bug complex, Ukrainian Shield, showed that ultramafic magma was contaminated by the material of the country gneiss enderbites. The age of the zircons of 2.81 ± 0.05 Ga corresponds to the period of ultramafic magmatism within the Bug complex. Previously, this peak of endogenic activity was considered the stage of manifestation of metamorphism and magmatism of mafic composition.

Interaction of Components in Cu–Fe Glass-Forming Melts with Titanium, Zirconium, and Hafnium. III. Modeling of Metastable Phase Transformations with Participation of Liquid Phase

Theoretical bases for calculation of metastable phase transformations with participation of supercooled melts, such as immiscibility and glass formation, are considered. A dataset of the model parameters for the thermodynamic properties of phases in the Cu–Fe–(Ti, Zr, Hf) systems is presented for performing corresponding calculations in the framework of the CALPHAD method. The diagrams of metastable phase transformations with participation of supercooled liquid alloys and terminal solid solutions are calculated. The composition regions of metastable immiscibility of supercooled ternary liquid alloys are presented. The composition regions for producing rapidly quenched amorphous Cu–Fe–(Ti, Zr, Hf) alloys are theoretically estimated. The production of ternary immiscible rapidly quenched amorphous alloys in the composition region with x Me ≈ 0.1–0.2 is predicted. Bulk amorphous alloys are expected to be produced in the composition region with x Me ≈ 0.3–0.6.

Interaction of Components in Cu–Fe Glass-Forming Melts with Titanium, Zirconium, and Hafnium. II. Temperature–Concentration Dependence of Thermodynamic Mixing Functions

The formalism of the associated solution model for ternary melts with both strongly interacting components and components exhibiting repulsion is described. A set of model parameters that adequately describe the thermodynamic properties of melts of three-component Cu–Fe–(Ti, Zr, Hf) systems and boundary two-component systems is established. The thermodynamic mixing functions of ternary melts are calculated in the entire range of compositions and over a wide range of temperatures. In most of the concentration triangle, the thermodynamic properties of melts are characterized by negative deviations from ideal behavior. The thermodynamic properties of melts adjacent to the copper–iron side of the concentration triangle are characterized by positive deviations from the Raoult law. The range of values and topology of the excess thermodynamic mixing functions of Cu–Fe–(Ti, Zr, Hf) melts are determined by pair interactions of the components.

Hafnium and neodymium isotopes and REY distribution in the truly dissolved, nanoparticulate/colloidal and suspended loads of rivers in the Amazon Basin, Brazil

Radiogenic isotopes in river sediments and river waters have been widely used in provenance studies, as these samples naturally integrate the geology/chemistry of the entire catchment. While the Hf and Nd isotope systems are coupled during igneous processes, they are decoupled during supergene processes at the Earth’s surface, which is reflected by the isotope composition of riverine sediments. We present the first data for both Hf and Nd isotope compositions of the dissolved (0.2μm-filtrates rich in nanoparticles and colloids, NPCs) and the truly dissolved (1kDa-ultrafiltrates) load of rivers. Hafnium and Nd isotope compositions and concentrations of the Rare Earths and Yttrium (REY) and Hf were determined for suspended particles (>0.2μm) as well as for the dissolved and the truly dissolved load of the Rio Solimões, the Amazon’s largest tributary draining the Andes, and of the Rio Negro, an organic NPC- and particle-rich river draining the rainforest of northern Amazonia. We also analyzed the Nd isotope compositions of suspended sediments and 0.2μm-filtered water samples from the Amazon River and its tributaries Rio Tapajos, Rio Xingu and Rio Jari.Our novel results clearly show that the decoupling of the Hf and Nd isotope systems is related to incongruent weathering processes on the continent, as this decoupling can already be observed in the different Hf and Nd pools, i.e. in the particulate, the NPC-dominated dissolved and the truly dissolved load of rivers. In the Rio Negro and Rio Solimões, a strong particle size-dependent difference in Hf isotope composition is observed. Values of εHf become more radiogenic as filter poresize decreases, which can be related to the density- and size-dependent distribution of Hf-rich minerals, e.g. zircons, and their absence from the truly dissolved pool. In contrast, the Nd isotope composition of Amazonian river waters reflects that of their catchment geology. Tributaries draining the Precambrian Brazilian and Guyana shields show very unradiogenic εNd values of −19 to −25 in their dissolved load, whereas the Rio Solimões draining the Andes yields a more radiogenic εNd signal of only −7. The dissolved Nd isotope composition of the Amazon is dominated by its Andean tributaries and averages at −8. Although Nd isotope compositions are thought to not being fractionated by Earth surface processes, significant differences of 1.3–1.9 ε-units can be observed between the dissolved and suspended loads in the Amazon River and its main tributary, the Rio Solimões. In these rivers, the dissolved load is more radiogenic than the suspended sediment, which is likely due to incongruent weathering and related mineral sorting in the Andean headwaters. In contrast, the organic-rich and mineral-poor shield rivers do not show a difference between the truly dissolved, dissolved and suspended load, as the Nd in all these pools is controlled by surface- and solution-complexation and hence isotopically homogenized by continuous exchange and re-equilibration.

Interaction of Components in Cu–Fe Glass-Forming Melts with Titanium, Zirconium, and Hafnium. I. Calorimetric Study of Mixing Enthalpies

The partial mixing enthalpies of titanium, zirconium, and hafnium with liquid copper and iron alloys are studied by high-temperature calorimetry. The studies are carried out at a temperature of 1873 K along the sections with constant ratios x Cu/x Fe = 3, 1, and 1/3. Along all the studied sections, these functions are negative. The integral mixing enthalpies of components in the Cu–Fe–(Ti, Zr, Hf) systems along the studied sections are calculated by integrating the Gibbs–Duhem equation. The ΔH functions for ternary Cu–Fe–(Ti, Zr, Hf) melts are characterized by positive values in the vicinity of the binary Cu–Fe system and show negative values in a range of compositions with x Me > 0.1 (Me = = Ti, Zr, Hf).

Thermodynamic Properties of Iron Melts with Titanium, Zirconium, and Hafnium

The literature data on the enthalpies of mixing and thermodynamic activities of Fe–Ti, Fe–Zr, and Fe–Hf liquid alloys are summarized. It is shown that the thermodynamic properties of these systems are characterized by significant negative deviations from the ideal behavior. In the framework of the associated solution model, the composition and temperature dependences of the thermodynamic functions of mixing for the Fe–Ti, Fe–Zr, and Fe–Hf systems are described. The temperature dependence of the thermodynamic properties of the considered systems is characterized by increase in negative deviations from the ideality with decreasing temperature and increasing thermodynamic stability of supercooled melts. Analysis of the degree of short-range order in the system melts, estimated as the total mole fraction of associates Σxass at the glass transition temperature, allows us to successfully interpret the known composition ranges of glass transition for the Fe–Zr and Fe–Hf melts and predict the composition range of glass transition for the Fe–Ti melts.

Accurate Prediction of Copolymerization Statistics in Molecular Olefin Polymerization Catalysis: The Role of Entropic, Electronic, and Steric Effects in Catalyst Comonomer Affinity

Accurate in silico prediction of copolymerization performance of olefin polymerization catalysts is demonstrated. It is shown by the example of 19 metallocene and post-metallocene group IV metal (Ti, Zr, Hf) systems that DFT (M06-2X(PCM)/TZ//TPSSTPSS/DZ) can accurately describe the copolymerization factor re: i.e., the competition of ethene and propene for insertion in metal n-alkyl bonds. Experimental re values were computationally reproduced with a mean average deviation (MAD) and maximum deviation of only 0.2 and 0.5 kcal/mol, respectively. Both dispersion and solvent corrections play a crucial role in achieving this accuracy. Ethene insertion is found to be entropically favored for all catalysts due to a combination of symmetry factors and less congested insertion geometries. The enthalpic preference for either ethene or propene is catalyst dependent. The predictions are based on straightforward calculation of relevant insertion transition state energies; there are no indications for a shift in rate-l...

Electronic structures, magnetic properties and spin-orbital coupling effects of aluminum nitride monolayers doped by 5d transition metal atoms: possible two-dimensional long-range magnetic orders

The magnetism of two-dimensional material is an important research topic. In particular, the long-range magnetic order of two-dimensional material is of great significance in theoretical research and practical application. According to the Mermin-Wagner theory, the isotropic Heisenberg model in a two-dimensional system cannot produce long-range magnetic orders at non-vanishing temperatures. Considering the existence of strong magnetic anisotropy, possible two-dimensional long-range magnetic orders may exist in 5d atom doped two-dimensional aluminum nitride (AlN) monolayer. This research is performed by first-principles calculations based on the density functional theory. Geometries, electronic structures, magnetic properties, and magnetic anisotropy energies from spin-orbital coupling effects in AlN monolayers doped by 5d transition metal atoms (Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg) are calculated. Four kinds of supercells are used in the calculation, i.e, 22, 33, 44, and 55, with one aluminum atom substituted by one 5d atom. Projection augmented wave method is used to describe the interaction between the valence electrons and the ions. The plane wave is used to expand the wave function of the valence electron. For an optimized geometry, the bond length between the 5d metal atom and the nearest N atom is the largest in Hg-doped supercells, which is 2.093 , followed by the Au, Hf, Pt, Ta, and Ir according to the order of bond length magnitude. For the densities of states (DOSs), obvious impurity energy levels appear in the forbidden bands. For all the supercells, spin-up and spin-down DOSs of Ta and Ir doped systems are symmetric, indicating non-magnetic states. DOSs of Hf, W, Re, and Os doped systems are asymmetric, indicating magnetic states. For Pt, Au, and Hg, DOSs are symmetric in 22 supercells, but asymmetric in the 33, 44, and 55 supercells. Total magnetic moments and the spin densities are also given. In 55 supercells, they are 1.00, 0.00, 0.39, 1.99, 1.17, 0.00, 1.00, 2.00, and 1.00 for Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg, respectively. The magnetic moment is mainly concentrated in the vicinity of the 5d atoms. The energy differences between ferromagnetic and antiferromagnetic states are calculated. For Hf, Re, Pt and Au systems, the differences in 48 supercells reach the maximum values of -187.2563 meV, 286.2320 meV, -48.0637 meV and -61.7889 meV, respectively. The results indicate that there is a strong interaction between the magnetic centers. Magnetic anisotropy energy originating from spin-orbital effect is calculated in the 44 supercells. For the Re system, it is the highest, reaching 11.622 meV. For W, Os, and Au, the values are larger than 1 meV, showing strong magnetic anisotropies. The magnetic anisotropy can produce a spin wave energy gap, resulting in long-range magnetic orders. Based on the results above, it is predicted that with appropriate 5d atoms and suitable doping concentration, two-dimensional long-range magnetic orders may exist in 5d transition metal atom doped AlN monolayers.

Structural Transformations and Thermal Expansion in Aluminum Alloys of the Al–Ni–Zr and Al–Ni–Hf Systems

We study the structural transformations in Al–Ni–Zr and Al–Ni–Hf alloys in the concentration regions with high contents of Al. The eutectoid transformation of the Zr6Ni8Al15 phase into a microscopic mixture of compounds NiAl + ZrNi0.5Al1.5 and the peritectic formation of HfNi0.35Al1.65 from a mixture of HfNi2Al5 and Hf6Ni8Al15 are discovered. The temperature dependence of the structural parameters is analyzed and the thermal expansion coefficient for the HfNi0.35Al1.65 phase is found within the range 393–723°K.

Whole-rock Nd–Hf isotopic study of I-type and peraluminous granitic rocks from the Chinese Altai: Constraints on the nature of the lower crust and tectonic setting

The nature of the lower crust and tectonic setting of the Chinese Altai in the early to middle Paleozoic are still hotly debated. Decoupling between zircon Hf and whole-rock Nd isotopic systems for granites results in different interpretations for the above issues. In order to solve the problem, whole-rock Nd–Hf isotopic analyses were conducted on representative early to middle Paleozoic I-type granite and strongly peraluminous granites and rhyolites from the Chinese Altai. The I-type granites show metaluminous to weakly peraluminous feature and have εNd(t) values ranging from −2.2 to +0.8 and εHf(t) from +3.9 to +12.9, respectively. The strongly peraluminous granites and rhyolites have similar εNd(t) and εHf(t) values ranging from −3.0 to +1.7 and from +2.1 to +10.4, respectively. All samples plot above the Terrestrial Array on Nd–Hf isotopic diagram, indicating significant Nd–Hf isotopic decoupling in the magma sources. These samples show flatten HREE pattern and have Lu/Hf ratios similar to the average crust, suggesting that Nd–Hf isotopic decoupling was not originated from an ancient basement with elevated Lu/Hf ratios. The observed isotopic decoupling is similar to those modern island arcs, such as the Lesser Antilles and Sunda, where Nd selectively enriched over Hf due to metasomatism in the mantle wedge and consequently resulted in decoupling between the Sm–Nd and Lu–Hf isotopic systems. Our results, combined with the available data, show that prolonged subduction and crust–mantle interaction caused the Nd–Hf isotopic decoupling in the lithospheric mantle beneath the Chinese Altai. The crust of the Chinese Altai was extracted from the lithospheric mantle and inherited the Nd–Hf isotopic decoupling feature. Therefore, the Hf, rather than Nd, isotopic data more faithfully reflect the nature of the lower crust that was quite juvenile in the Paleozoic, and the Chinese Altai represents an early Paleozoic magmatic arc possibly built near western Mongolia.

Multicomponent diffusion in aluminosilicate garnet: coupling effects due to charge compensation

ABSTRACTThree kinds of multicomponent diffusion effects, arising from three distinct physical mechanisms, are evident in stranded diffusion profiles at the rims of partially resorbed garnets from the contact aureole of the Makhavinekh Lake Pluton, northern Labrador. Profiles that display a subtle maximum in Ca concentration are explained by the prevailing ideal mean-field theory of multicomponent diffusion, but models implementing that theory cannot replicate inverted profiles for Li and internal maxima for Nd, Sm, and Eu. The anomalous profiles are quantitatively reproduced, however, by numerical simulations employing a model based on coupled movement of charge-compensating groups during diffusional transport of yttrium and the rare-earth elements (Y+REEs). An alkali-type charge-compensation mechanism for the heterovalent substitution of Y+REEs on dodecahedral sites in garnet produces direct charge coupling between Li+ and (Y+REE)3+ and leads to co-diffusion of Li+-(Y+REE)3+ pairs, with the result that Li profiles closely mimic those for Y+REEs. A menzerite-type charge-compensation mechanism produces indirect charge coupling among all Y+REE components, with the result that the fluxes of low-abundance REEs become partly dependent on the fluxes of Y+REEs present in higher abundance. These findings have implications for the robustness of Li profiles in garnet as monitors of fluid–rock interaction, for geochronology based on the Sm–Nd and Lu–Hf systems, and for future experimental attempts to quantify rates of diffusion in garnet.

Impact of HF-based cleaning solutions on via resistance for sub-10 nm BEOL structures

In this work, ultra-dilute HF systems with the addition of functional hydrocarbon as an additive at elevated temperatures were evaluated to remove the post reactive ion etching (RIE) residues in a controlled chamber with ambient O2 concentration <30ppb. Controlling the HF and additive concentration was critical to achieve minimum dielectric loss (<2Å) and to suppress the formation of copper oxides while effectively removing post etch residues (PER). Cu 2p XPS peaks confirmed the removal of residues from the Cu and ULK sidewalls. An oxide free Ta/TaN liner and Cu surface was achieved and confirmed using time of flight secondary ion mass spectroscopy (TOF-SIMS). In addition, the impact of HF solution was electrically evaluated by measuring via resistance and yield. A clear trend in via resistance reduction and yield improvement (40%) was observed with applying the optimized cleaning conditions when compared to the control samples.

Metallic glass formation in Cu–Ni–Ti (Zr, Hf) systems studied by thermodynamic calculations

The glass formation regions for the family of Cu–Ni–Ti (Zr, Hf) systems have been calculated. The composition dependence of the glass forming ability was predicted and discussed in terms of the mixing enthalpy and atomic size effect.

Hf and Nd isotope systematics of early Archean komatiites from surface sampling and ICDP drilling in the Barberton Greenstone Belt, South Africa

![][1] To constrain the origin of komatiites from the Barberton Greenstone Belt, South Africa, we measured 147Sm-143Nd and 176Lu-176Hf compositions for 18 komatiites from core obtained during the International Continental Drilling Program in the Komati Formation of the Barberton Belt, as well as 33 komatiites from surface outcrops of the Komati, Hooggenoeg, and Weltevreden Formations, these latter for purposes of comparison between core and surface samples. Magmatic clinopyroxene from surface samples near the drill site was also analyzed. For the Lu-Hf isotope system, the Komati Formation core and surface samples including the clinopyroxene define a linear array whose slope corresponds to an age of 3426 ± 16 Ma (MSWD = 118; ɛHf(T) = +2.2), which is slightly younger than the accepted age of the rocks (3.48 Ga). The Sm-Nd isotope data for the same set of samples likewise fall along a linear array also yielding a younger age of 3339 ± 12 Ma (MSWD = 42; ɛNd(T) = +2.8). The high MSWD for both isotope systems indicate substantial scatter at variance with normal magmatic processes, likely implying element mobility disturbing even these relatively robust isotopic systems shortly after eruption of the lavas. The average initial ɛNd and ɛHf of the core samples at 3.48 Ga are +0.45 and +1.4, respectively, in overall accordance with the positive errorchron intercepts and a depleted mantle source at 3.5 Ga. In contrast, the clinopyroxene and their host rocks have strongly positive ɛHf(T) of about +5 and negative ɛNd(T) of about −2. Given the overall scatter of the whole-rock data, the most robust constraint on the composition of the komatiite source comes from the clinopyroxene. Their positive ɛHf(T) is in line with, though somewhat higher than other results from komatiites from the Komati Formation, but their negative ɛNd(T) is unexpected in that it indicates a source with long-term low Sm/Nd, which is at odds with its long-term high Lu/Hf. This signature is also found in the trace element compositions of some of the komatiites, such as moderately enriched LREE, negative Hf anomalies, and low Hf/Sm ratios. The origin of these features is uncertain but one possibility is that the discordance between the Hf and Nd isotope systems reflects the presence of deep-sea sediments in the source of some of the Barberton komatiites. The possible presence of a surface component in an ancient deep mantle source has wide-ranging implications for mantle-crust interaction and dynamics in the early Earth and for constraining a minimum age for the onset of plate tectonics. [1]: /embed/graphic-1.gif

The DFT and MP2 based computational scrutiny on blue-shifted H–F stretching vibrational frequencies in hydrogen-fluoride complexes with nitriles: Insights into the decisive role of intermolecular hydrogen bonding (IMHB) in ground and electronic excited states

In the current study, the RCN⋯HF (R=H, F, Cl, Br, CN, OH, SH, NH2, NO2 and CH3) systems are studied as the interest sample for the consideration of different measures of H-bond strength. The calculations are conducted by means of DFT (B3LYP) and MP2 methods in conjunction with the 6-311++G∗∗ and aug-cc-pVTZ basis sets for geometry optimization of complexes and monomers and also evaluation of the intermolecular interaction energies. It is found that a blue-shifted hydrogen bonding (HB) in RCN⋯HF complexes in that N atom of the nitrile molecules acts as a proton-acceptor. The nature of intermolecular hydrogen bond has been investigated by means of the Bader theory of Atoms In Molecules (AIM) and Natural Bond Orbital (NBO) analysis. The calculated highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO, respectively) energies show that charge transfer occurs within the studied complexes. The results obtained from molecular orbital interactions play an important role toward characterization of the chemical reactivity and kinetic stability of the H-bonded systems. Likewise, the strengthening of the intermolecular hydrogen bond and moving the 1H chemical shift of participating H atom in the hydrogen bridge to up fields are associated with each other. The obtained results indicate a strong influence of the R substituent on the hydrogen bond strength. Moreover, the excited-state properties of intermolecular hydrogen bonding in the RCN⋯HF systems have been investigated theoretically using the time-dependent density functional theory (TD-DFT) method. Besides, numerous correlations between topological, geometrical and energetic parameters are also found.

Geochronology and Thermochronology Using Apatite: Time and Temperature, Lower Crust to Surface

Apatite can provide geologists with an exceptionally wide range of ages and temperatures to investigate processes that operate from Earth's surface right down to the lower crust. Apatite is a widespread accessory mineral in igneous, metamorphic, and clastic sedimentary rocks and can be dated using four radioactive decay schemes, each with a different temperature window for isotopic closure: Lu–Hf (675–750 °C); U–Pb (350–550 °C); apatite fission track (60–110 °C); (U–Th)/He (40–80 °C). The fission-track and (U–Th)/He methods are popular for studying upper-crustal and near-surface processes, whereas the U–Pb and Lu–Hf systems are used to investigate the thermal, tectonic, and magmatic histories of the deeper crust.