Crystals, Volume 8, Issue 3 (March 2018) – 34 articles

The charge transfer salts α-DT-TTF[Au(dcdmp)₂] (1), BET-TTF[Au(dcdmp)₂] (2M and 2T), α-DT-TTF[Cu(dcdmp)₂] (3), ET[Cu(dcdmp)₂] (4), (BET-TTF)₂[Cu(dcdmp)₂] (5), (ET)₂[Ni(dcdmp)₂] (6), and α-mtdt[Cu(dcdmp)₂] (7) were obtained by electrocrystallization of different electron donor molecules derived from TTF (α-DT-TTF = alpha-dithiophene-tetrathiafulvalene; BET-TTF = (bis(ethylenethio)tetrathiafulvalene; ET = bis(ethylenedithio)-tetrathiafulvalene; α-mtdt = alpha-methylthiophenetetrathiafulvalene) in the presence of transition metal complex [M(dcdmp)₂] (M = Au (III), Cu (III) and Ni (II)) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 2 (2M and 2T) have a similar packing pattern composed of mixed stacks of alternating donor-acceptor molecules. For (BET-TTF)[Au(dcdmp)₂] two different crystal structures (2M and 2T) were obtained indicating polymorphism. Compounds 3 and 4 are isostructural being composed of zigzag chains of alternating donor and acceptor molecules. The salts with a 2:1 stoichiometry, (BET-TTF)₂[Cu(dcdmp)₂] (5), and (ET)₂[Ni(dcdmp)₂] (6) present the donor molecules fully oxidized and [M(dcdmp)₂] (M = Ni and Cu) in a dianionic state. The salt of the dissymmetric donor α-mtdt with [Cu(dcdmp)₂], α-mtdt[Cu(dcdmp)₂] (7) has a crystal structure composed of segregated donor stacks that are positioned in a head-to-head fashion and alternate with the anion stacks. All charge transfer salts (1–7) are modest semiconductors with conductivities in the range 10⁻¹–10⁻⁵ S/cm, with the highest values obtained in α-DT-TTF salts, compounds 1 and 3. Full article

The opposing effects of high pressure (in the GPa range) and the Jahn-Teller distortion led to many intriguing phenomena which are still not well understood. Here we report a combined experimental-theoretical study on the high-pressure behavior of an archetypical Jahn-Teller system, copper difluoride (CuF₂). At ambient conditions this compound adopts a distorted rutile structure of P2₁/c symmetry. Raman scattering measurements performed up to 29 GPa indicate that CuF₂ undergoes a phase transition at 9 GPa. We assign the novel high-pressure phase to a distorted fluorite structure of Pbca symmetry, iso-structural with the ambient-pressure structure of AgF₂. Density functional theory calculations indicate that the Pbca structure should transform to a non-centrosymmetric Pca2₁ polymorph above 30 GPa, which, in turn, should be replaced by a cotunnite phase (Pnma symmetry) at 72 GPa. The elongated octahedral coordination of the Cu²⁺ cation persists up to the Pca2₁–Pnma transition upon which it is replaced by a capped trigonal prism geometry, still bearing signs of a Jahn-Teller distortion. The high-pressure phase transitions of CuF₂ resembles those found for difluorides of transition metals of similar radius (MgF₂, ZnF₂, CoF₂), although with a much wider stability range of the fluorite-type structures, and lower dimensionality of the high-pressure polymorphs. Our calculations indicate no region of stability of a nanotubular polymorph observed for the related AgF₂ system. Full article

Four new solvent-induced Co(II) complexes with chemical formulae [{CoL(μ₂-OAc)(MeOH)}₂Co] (1), [{CoL(μ₂-OAc)(EtOH)}₂Co] (2), [{CoL(μ₂-OAc)(Py)}₂Co] (3) and [{CoL(μ₂-OAc)(DMF)}₂Co] (4) (H₂L = 4-nitro-4′-chloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol) have been synthesized and characterized by elemental analyses, FT–IR, UV–Vis spectra and single-crystal X-ray diffraction. Each of the prepared complexes, crystallizing in the space groups P–1 (1 and 4), P2₁/n (2) and P2₁/c (3), consists of three Co(II) atoms, two completely deprotonated (L)²⁻ units, two μ₂-acetato ligands and two coordinated solvent molecules. Although the four complexes 1–4 were synthesized in different solvents, it is worthwhile that the Co(II) atoms in the four complexes 1–4 adopt hexa–coordinated with slightly distorted octahedral coordination geometries, and the ratio of the ligand H₂L to Co(II) atoms is 2:3. The complexes 2–4 possess a self-assembled infinite 1D, 2D and 1D supramolecular structures via the intermolecular hydrogen bonds, respectively. Magnetic measurement was performed in the complex 3. Full article

In an isostructural series of anion radical salts β′-(Me_4-xEt_xZ)[Pd(dmit)₂]₂ (Z = P, As, Sb; x = 0, 1, 2), [Pd(dmit)₂]₂⁻ units form a two-dimensional Mott insulator layer with a quasi-isosceles triangular lattice. The anisotropy of the triangular lattice is characterized by a ratio of interdimer transfer integrals, t′/t. The crystal structures of EtMe₃Sb, Me₄Sb, Me₄As, and Et₂Me₂As salts were determined in the range of 5–295 K by the single crystal X-ray diffraction technique. Interdimer transfer integrals, Fermi surface, and band structures at low temperatures were calculated by the tight binding method and the first-principles density-functional theory (DFT) method based on experimentally obtained crystal structures. Interdimer transfer integrals increased with lowering temperature. At 5 K, the ratio t′/t decreased by about 15% from the room temperature value in every salt. The relationship between the transfer integrals and interdimer S⋯S distances indicated that the change of the t′/t value with temperature was due to a thermal contraction, rather than the arch-shaped molecular distortion of the Pd(dmit)₂ molecule associated with the cation dependence of t′/t. Full article

The optical conductivity in the charge order phase is calculated in the two-dimensional extended Hubbard model describing an organic Dirac electron system $\alpha$ -(BEDT-TTF) ${}_2$ I ${}_3$ using the mean field theory and the Nakano-Kubo formula. Because the interband excitation is characteristic in a two-dimensional Dirac electron system, a peak structure is found above the charge order gap. It is shown that the peak structure originates from the Van Hove singularities of the conduction and valence bands, where those singularities are located at a saddle point between two Dirac cones in momentum space. The frequency of the peak structure exhibits drastic change in the vicinity of the charge order transition. Full article

In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba_0.9La_0.1Zr_0.25Sn_0.25In_0.5O_3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This can be correlated with an appearance of the electronic hole component of the conductivity at high temperatures. The collected electrical conductivity relaxation data allowed to calculate chemical diffusion coefficient D and surface exchange reaction coefficient k, as well as respective activation energies of their changes on temperature. Presented results are supplemented with a systematic characterization of the structural properties of materials synthesized at different temperatures, amount of incorporated water after hydration in different conditions, influence of water content on the crystal structure, as well as electrical conductivity in dry, H₂O- and D₂O-containing air, which enabled to evaluate proton (deuterium) conductivity. Full article

In this paper, a method to obtain the CuInGaSe₂ (CIGS) absorber layer with an appropriate selenium content is put forward, in which a Se-rich target is used to deposit a CIGS thin-film and this film is annealed in a Se-free inert atmosphere. The key issue of this method is the preparation of a Se-rich target with a homogeneous composition and a high-density. The formation mechanism of CuInSe₂ and CuGaSe₂ is investigated and the results point to the intermediate phase Cu_2−xSe playing a role of a nucleation core. The sintering densification trajectory of the target with the addition of extra selenium is researched. Additionally, an effective way to avoid the sintering defects is proposed. Finally, a conversion efficiency of 11.2% for the CIGS solar cell is reached by sputtering from the obtained Se-rich target. Full article

Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with La-doped Strontium Titanate (LST). This particular cermet has very interesting properties that can be used in different fields of application, namely: mechanical robustness provided by the metal foam; and chemical stability in harsh conditions of temperature and atmosphere by promotion of a thin protective layer of alumina (Al₂O₃); high electronic conductivity given by a percolating ceramic conducting phase, i.e., La-doped Strontium Titanate. In this paper, its application as a current collector in a metal-supported Solid Oxide Fuel Cells (SOFC) was studied. Firstly, the electronic properties of different compositions, stoichiometric and under stoichiometric, of LST were analyzed to choose the best one in terms of conductivity and phase purity. Then, LST chemical stability was studied in the presence of Al₂O₃ at different temperatures, gas compositions and aging times. Finally, stability and conductivity of LST-impregnated NiCrAl foam composite materials were measured, and LST was found to be fully compatible with the NiCrAl foam, as no reactions were detected in oxidizing and reducing atmosphere after up to 300 h operation at 750 °C and 900 °C between the Al₂O₃ layer and LST. Results showed that the composite is suitable as a current collector in innovative designs of metal-supported SOFC, like the Evolve cell, in which the metallic part is supposed not only to provide the structural stability to the cell, but also to play the role of current collector due to the impregnation of ceramic material. Full article

Alumina (α-Al₂O₃) is one of the representative high-temperature structural materials. Dislocations in alumina play an important role in its plastic deformation, and they have attracted much attention for many years. However, little is known about their core atomic structures, with a few exceptions, because of lack of experimental observations at the atomic level. Low-angle grain boundaries are known to consist of an array of dislocations, and they are useful to compose dislocation structures. So far, we have systematically fabricated several types of alumina bicrystals with a low-angle grain boundary and characterized the dislocation structures by transmission electron microscopy (TEM). Here, we review the dislocation structures in $\left\{11\overline{2}0\right\}/\left[0001\right]$ , $\left\{11\overline{2}0\right\}/\langle 1\overline{1}00\rangle$ , $\left\{1\overline{1}00\right\}/\langle 11\overline{2}0\rangle$ , $\left(0001\right)/\langle 1\overline{1}00\rangle$ , $\left\{\overline{1}104\right\}/\langle 11\overline{2}0\rangle$ , and $\left(0001\right)/\left[0001\right]$ low-angle grain boundaries of alumina. Our observations revealed the core atomic structures of b = $1/3\langle 11\overline{2}0\rangle$ edge and screw dislocations, $\langle 1\overline{1}00\rangle$ edge dislocation, and $1/3\langle \overline{1}101\rangle$ edge and mixed dislocations. Moreover, the stacking faults on $\left\{11\overline{2}0\right\}$ , $\left\{1\overline{1}00\right\}$ , and $\left(0001\right)$ planes formed due to the dissociation reaction of the dislocations are discussed, focusing on their atomic structure and formation energy. Full article

Experimental determination of electron density distribution in crystals by means of high-resolution X-ray diffraction allows, among others, for studying the details of intra- and inter-molecular interactions. In case of co-crystals, this method may help in finding the conditions of creating such species. The results of such analysis for two co-crystals containing betaines, namely trigonelline (TRG: nicotinic acid N-methylbetaine, IUPAC name: 1-methylpyridinium-3-carboxylate) and N-methylpiperidine betaine (MPB: 1-methylpiperidinium-1-yl-carboxylate) with p-hydroxybenzoic acid (HBA) are reported. TRG-HBA crystallizes as a hydrate. For both of the co-crystals, high-quality diffraction data were collected up to sinθ/λ = 1.13 Å⁻¹. Hansen-Coppens multipolar model was then applied for modelling the electron density distribution and Atoms-In-Molecules approach was used for detailed analysis of interactions in crystals. A number of intermolecular interactions was identified, ranging from strong O-H···O hydrogen bonds through C-H···O to C-H···π and π···π interactions. Correlations between the geometrical characteristics of the contacts and the features of their critical points were analyzed in detail. Atomic charges show that in zwitterionic species there are regions of opposite charges, rather than charges that are localized on certain atoms. In case of MPB-HBA, a significant charge transfer between the components of co-crystal (0.5 e) was found, as opposed to TRG-HBA, where all of the components are almost neutral. Full article

Li₂B₁₂H₁₂ is commonly considered as a boron sink hindering the reversible hydrogen sorption of LiBH₄. Recently, in the dehydrogenation process of LiBH₄ an amorphous H-deficient Li₂B₁₂H_12−x phase was observed. In the present study, we investigate the rehydrogenation properties of Li₂B₁₂H_12−x to form LiBH₄. With addition of nanostructured cobalt boride in a 1:1 mass ratio, the rehydrogenation properties of Li₂B₁₂H_12−x are improved, where LiBH₄ forms under milder conditions (e.g., 400 °C, 100 bar H₂) with a yield of 68%. The active catalytic species in the reversible sorption reaction is suggested to be nonmetallic Co_xB (x = 1) based on ¹¹B MAS NMR experiments and its role has been discussed. Full article

Molecular complexation is a strategy used to modify the physicochemical or biopharmaceutical properties of an active pharmaceutical ingredient. Solvent assisted grinding is a common method used to obtain solid complexes in the form of cocrystals. Lidocaine is a drug used as an anesthetic and for the treatment of chronic pain, which bears in its chemical structure an amide functional group able to form hydrogen bonds. Polyphenols are used as cocrystal coformers due to their ability to form O–H···X (X = O, N) hydrogen bond interactions. The objective of this study was to exploit the ability of phloroglucinol to form molecular complexes with lidocaine by liquid assisted grinding. The formation of the complex was confirmed by the shift of the O–H and C=O stretching bands in the IR spectra of the polycrystalline ground powders, suggesting the formation of O–H···O=C hydrogen bonds. Hydration of the complexes also was confirmed by IR spectroscopy and by powder X-ray diffraction. The molecular structure was determined by single crystal X-ray diffraction. Full article

The influence of vibration on friction at the nanoscale was studied via molecular dynamics (MD) simulations. The results show that average friction increases in a high-frequency range. This can be attributed to the vibration of the tip following vibration excitation, which results in peaks of repulsive interaction between tip and substrate and leads to higher friction. However, when the frequency is lower than a certain value, friction decreases. This is because vibration excitation results not in an obvious vibration of the tip but in a slightly larger interface distance, which leads to a decrease in friction. Full article

The strain rate sensitivity (SRS) and dislocation activation volume are two inter-related material properties for understanding thermally-activated plastic deformation, such as creep. For face-centered-cubic metals, SRS normally increases with decreasing grain size, whereas the opposite holds for body-center-cubic metals. However, these findings are applicable to metals with average grain sizes greater than tens of nanometers. Recent studies on mechanical behaviors presented distinct deformation mechanisms in multilayers with individual layer thickness of 20 nanometers or less. It is necessary to estimate the SRS and plastic deformation mechanisms in this regime. Here, we review a new nanoindentation test method that renders reliable hardness measurement insensitive to thermal drift, and its application on SRS of Cu/amorphous-CuNb nanolayers. The new technique is applied to Cu films and returns expected SRS values when compared to conventional tensile test results. The SRS of Cu/amorphous-CuNb nanolayers demonstrates two distinct deformation mechanisms depending on layer thickness: dislocation pileup-dominated and interface-mediated deformation mechanisms. Full article

Basal dislocations having a Burgers vector of 1/3<2 $\overline{1}$ $\overline{1}$ 0> in zinc oxide (ZnO) with the wurtzite structure are known to strongly affect physical properties in bulk. However, the core structure of the basal dislocation remains unclear. In the present study, ZnO bicrystals with a {2 $\overline{1}$ $\overline{1}$ 0}/<01 $\overline{1}$ 0> 2° low-angle tilt grain boundary were fabricated by diffusion bonding. The resultant dislocation core structure was observed by using scanning transmission electron microscopy (STEM) at an atomic resolution. It was found that a basal edge dislocation in α-type is dissociated into two partial dislocations on the (0001) plane with a separation distance of 1.5 nm, indicating the glide dissociation. The Burgers vectors of the two partial dislocations were 1/3<1 $\overline{1}$ 00> and 1/3<10 $\overline{1}$ 0>, and the stacking fault between the two partials on the (0001) plane has a formation energy of 0.14 J/m². Although the bicrystals have a boundary plane of {2 $\overline{1}$ $\overline{1}$ 0}, the boundary basal dislocations do not exhibit dissociation along the boundary plane, but along the (0001) plane perpendicular to the boundary plane. From DFT calculations, the stacking fault on the (0001) plane was found to be much more stable than that on {2 $\overline{1}$ $\overline{1}$ 0}. Such an extremely low energy of the (0001) stacking fault can realize transverse dissociation of the basal dislocation of ZnO. Full article

A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)₂I₃ under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. Moreover, the Dirac cones are highly tilted in a k-space. This system, thus, provides a testing ground for the investigation of physical phenomena in the multilayered, massless Dirac electron system with anisotropic Fermi velocity. Recently, the carrier injection into this system has been succeeded. Thus, the investigations in this system have expanded. The recent developments are remarkable. This effect exhibits peculiar (quantum) transport phenomena characteristic of electrons on the Dirac cone type energy structure. Full article

The geometries of the enol (E) and keto (K) forms of a crystalline salicylideneaniline molecular switch, (E)-2-methoxy-6-(pyridine-3-yliminomethyl)phenol (PYV3), have been determined using periodic density functional theory (DFT) calculations with a variety of exchange-correlation functionals (XCFs). They are compared to X-ray diffraction (XRD) data as well as to geometries obtained using empirical dispersion energy in the form of the second iteration of Grimme’s scheme, either with its original parameters (DFT-D2) or with parameters revised for the solid state (DFT-D*). Using DFT, a good agreement with experiment on the unit cell parameters is obtained with the PBEsol, PBEsol0, and ωB97X XCFs. DFT-D2 contracts the unit cell too much with all considered XCFs, whereas DFT-D* lessens this effect thus allowing B3LYP, PBE, and PBE0 to achieve reasonable agreement with respect to XRD data. When considering molecular geometries, both DFT and DFT-D* have a similar effect on the bond lengths, both systematically underestimating (overestimating) the length of the single (double) bonds (within 0.003 Å), as well as on valence angles attaining differences of 2° with respect to XRD data. The errors on the torsion angles are less spread out with DFT-D* (averaging 1°) than DFT for which only PBEsol, PBEsol0, and ωB97X perform well. Finally, the relative keto–enol energies, ΔE_KE, have been calculated, showing that the inclusion of dispersion energy stabilizes the keto form more than it does the enol form. This results in the PBE and PBEsol XCFs wrongly predicting the keto form as the most stable form. Full article

Organic-inorganic hybrid perovskite has attracted intensive attention from researchers as the gain medium in lasing devices. However, achieving electrically driven lasing remains a significant challenge. Modifying the devices’ structure to enhance the optically pumped amplified spontaneous emission (ASE) is the key issue. In this work, gold nanoparticles (Au NPs) are first doped into PEDOT: PSS buffer layer in a slab waveguide device structure: Quartz/PEDOT: PSS (with or w/o Au NPs)/CH₃NH₃PbBr₃. As a result, the facile device shows a significantly enhanced ASE intensity and a narrowed full width at half maximum. Based on experiments and theoretical simulation data, the improvement is mainly a result of the compound surface plasmon resonance, including simultaneous near- and far-field effects, both of which could increase the density of excitons excited state and accelerate the radiative decay process. This method is highly significant for the design and development and fabrication of high-performance organic-inorganic hybrid perovskite lasing diodes. Full article

Lithium niobate (LiNbO₃) is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. Doping LiNbO₃ with hafnium (Hf) has been shown to improve the resistance of the material to optical damage. Computer modelling provides a useful means of determining the properties of doped and undoped LiNbO₃, including its defect chemistry, and the effect of doping on the structure. In this paper, Hf-doped LiNbO₃ has been modelled, and the final defect configurations are found to be consistent with experimental results. Full article

Nanostructured materials have already become an integral part of our daily life. In many applications, ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics, aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y ${}^{3+}$ ions into the cubic structure of SrF ${}_2$ . As compared to pure nanocrystalline SrF ${}_2$ the ionic conductivity of Sr ${}_{1-x}$ Y ${}_x$ F ${}_{2+x}$ with $x=0.3$ increased by 4 orders of magnitude reaching $0.8\times {10}^{-5}\mathrm{S}{\mathrm{cm}}^{-1}$ at 450 K. We discuss the effect of YF ${}_3$ incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5. Full article

Comprehensive measurements of the pressure- and temperature-dependent dc-transport are combined with dielectric spectroscopy and structural considerations in order to elucidate the charge and anion orderings in the quasi-one-dimensional charge-transfer salts (TMTTF) ${}_{2}X$ with non-centrosymmetric anions X = BF ${}_4$ , ClO ${}_4$ and ReO ${}_4$ . Upon applying hydrostatic pressure, the charge-order transition is suppressed in all three compounds, whereas the influence on the anion order clearly depends on the particular compound. A review of the structural properties paves the way for understanding the effect of the anions in their methyl cavities on the ordering. By determining the complex dielectric constant $\widehat{ϵ}(\omega ,T)$ in different directions we obtain valuable information on the contribution of the anions to the dielectric properties. For (TMTTF) ${}_2$ ClO ${}_4$ and (TMTTF) ${}_2$ ReO ${}_4$ , ${ϵ}_{b^{\prime }}$ exhibits an activated behavior of the relaxation time with activation energies similar to the gap measured in transport, indicating that the relaxation dynamics are determined by free charge carriers. Full article

In this work we show the influence of material preparation technology on the thermoluminescent properties of single crystalline films (SCFs) of Ce³⁺-doped Lu₂SiO₅ (LSO) and Y₂SiO₅ (YSO) orthosilicates. LSO:Ce and YSO:Ce SCFs were grown by the liquid phase epitaxy method from two different melt-solutions based on PbO-B₂O₃ and Bi₂O₃ fluxes. Absorption, cathodoluminescence, and thermoluminescent properties of LSO:Ce and YSO:Ce SCFs grown from the two previously mentioned types of fluxes were compared, and results of spectrally resolved thermoluminescence measurements and thermoluminescent glow curves of SCFs recorded in different spectral ranges were presented. We have found that the observed differences in thermoluminescent properties of the SCFs under study can be caused by the domination of Ce⁴⁺ and Pb²⁺ emission centers in LSO:Ce and YSO:Ce SCFs grown using PbO-B₂O₃ flux, and Ce³⁺ and Bi³⁺ emission centers in the SCFs grown from Bi₂O₃ flux. Full article

Spin-crossover clusters with iron(II) high nuclearity are rare. By using 3,5-bis(pyridin-2-yl)-1,2,4-triazole (bptH) as the ligand with two bidentate chelating sites, we successfully obtained three pentanuclear iron(II) cluster helicate compounds [{Fe^II(μ-bpt)₃}₂Fe^II₃(μ₃-O)][Fe^II₂(μ-Br)(μ-bpt)(NCS)₄(H₂O)]·2H₂O·C₂H₅OH (1), [{Fe^II(μ-bpt)₃}₂Fe^II₃(μ₃-O)][Fe^II₂(μ-bpt)₂(NCS)₄] (2), and [{Fe^II(μ-bpt)₃}₂Fe^II₃(μ₃-O)]I₂·2C₂H₅OH (3). Research on single-crystal structure and magnetism has indicated that tuning the spin state of two iron(II) ions in axial direction is successfully realized by regulating the different counter anions: one apical [Fe^II(bpt)₃]⁻ unit exhibits spin-crossover behavior while the other [Fe^II(bpt)₃]⁻ unit remains in low spin state in 1, both apical ions are of high spin states in 2, and are of low spin states in 3. Full article

We report the structures and the nonresonant Raman spectra of hybrid systems composed of carbon fullerenes ( $C_{60}$ and $C_{70}$ ) encased within single walled boron nitride nanotube. The optimal structure of these systems are derived from total energy minimization using a convenient Lennard-Jones expression of the van der Waals intermolecular potential. The Raman spectra have been calculated as a function of nanotube diameter and fullerene concentration using the bond polarizability model combined with the spectral moment method. These results should be useful for the interpretation of the experimental Raman spectra of boron nitride nanotubes encasing $C_{60}$ and $C_{70}$ fullerenes. Full article

This special issue looks at the potential applications of GaN-based crystals in both fields of nano-electronics and optoelectronics. The contents will focus on the fabrication and characterization of GaN-based thin films and nanostructures. It consists of six papers, indicating the current developments in GaN-related technology for high-efficiency sustainable electronic and optoelectronic devices, which include the role of the AlN layer in high-quality AlGaN/GaN heterostructures for advanced high-mobility electronic applications and simulation of GaN-based nanorod high-efficiency light-emitting diodes for optoelectronic applications. From the results, one can learn the information and experience available in the advanced fabrication of nanostructured GaN-based crystals for nano-electronic and optoelectronic devices. Full article

Atomistic simulations are performed to probe the anisotropic deformation in the compressions of face-centred-cubic metallic nanoparticles. In the elastic regime, the compressive load-depth behaviors can be characterized by the classical Hertzian model or flat punch model, depending on the surface configuration beneath indenter. On the onset of plasticity, atomic-scale surface steps serve as the source of heterogeneous dislocation in nanoparticle, which is distinct from indenting bulk materials. Under [111] compression, the gliding of jogged dislocation takes over the dominant plastic deformation. The plasticity is governed by nucleation and exhaustion of extended dislocation ribbons in [110] compression. Twin boundary migration mainly sustain the plastic deformation under [112] compression. This study is helpful to extract the mechanical properties of metallic nanoparticles and understand their anisotropic deformation behaviors. Full article

Spin-frustrated monomer-type Mott insulator C₆₀^•− solids are discussed in this review article. For the C₆₀^•− solids, the interfullerene center-to-center distance (r) is the key parameter that controls the competition between covalent bond-formation, itinerancy, and spin frustration. Eight C₆₀^•− salts with various compositions and dimensionalities are reviewed. In all of these C₆₀^•− salts except one, neither bond-formation nor long-range magnetic ordering was observed down to low temperatures. A plot of Weiss temperature (|Θ_CW|) against r shows that |Θ_CW| grows rapidly below r = 10.0 Å. Full article

One-dimensional metal–organic coordination polymers make up a class of compounds with potential towards the development of practical, new magnetic materials. Herein, a rare example of an ABBABB coupled linear chain comprised of alternating dicopper(II) tetraacetate units bridged to copper(II) acetate monomer units via axial η²:η¹:µ₂ coordinated acetate is reported. Examination of the structure, determined by small molecule X-ray crystallography, shows that each Cu(II) ion is in a d_x2–_y2 magnetic ground state. Magnetic susceptibility and magnetization data were collected and, consistent with the structural interpretation, demonstrate that the Cu(II) dimer (paddlewheel) exhibits classic antiferromagnetic exchange, while the S = 1/2 Cu(II) monomer is uncompensated in the ground state (low temperature regime.) Data were therefore fitted to a modified Bleaney-Bowers model, and results were consistent with the only other reported chain in this class for which magnetic data are available. Full article

High-quality Ta-doped La₂Ti₂O₇ (Ta-LTO) single crystal of about 40 mm in length and 5 mm in diameter was successfully prepared by the optical floating zone method. An X-ray rocking curve reveals that the crystal of LTO has excellent crystalline quality. As-grown crystals were transparent after annealing in air and the transmittance is up to 76% in the visible and near-infrared region. X-ray diffraction showed that this compound possessed a monoclinic structure with P2₁ space group. The dielectric properties were investigated as functions of temperature (0~300 °C) and frequency (10² Hz~10⁵ Hz). Dielectric spectra indicated an increase in the room-temperature dielectric constant accompanied by a drop in the loss tangent as a result of the Ta doping. One relaxation was observed in the spectra of electric modulus, which was ascribed to be related to the oxygen vacancy. The dielectric relaxation with activation energy of 1.16 eV is found to be the polaron hopping caused by the oxygen vacancies. Full article

The coupling of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with 4-phenylthiazol-2-amine in molar ratio 2:3 at RT in CH2Cl2 leads to binuclear (diaminocarbene)PdII complex 3c. The complex was characterized by HRESI+-MS, 1H NMR spectroscopy, and its structure was elucidated by single-crystal XRD. Inspection of the XRD data for 3c and for three relevant earlier obtained thiazole/thiadiazole derived binuclear diaminocarbene complexes (3a EYOVIZ; 3b: EYOWAS; 3d: EYOVOF) suggests that the structures of all these species exhibit intra-/intermolecular bifurcated chalcogen bonding (BCB). The obtained data indicate the presence of intramolecular S•••Cl chalcogen bonds in all of the structures, whereas varying of substituent in the 4th and 5th positions of the thiazaheterocyclic fragment leads to changes of the intermolecular chalcogen bonding type, viz. S•••π in 3a,b, S•••S in 3c, and S•••O in 3d. At the same time, the change of heterocyclic system (from 1,3-thiazole to 1,3,4-thiadiazole) does not affect the pattern of non-covalent interactions. Presence of such intermolecular chalcogen bonding leads to the formation of one-dimensional (1D) polymeric chains (for 3a,b), dimeric associates (for 3c), or the fixation of an acetone molecule in the hollow between two diaminocarbene complexes (for 3d) in the solid state. The Hirshfeld surface analysis for the studied X-ray structures estimated the contributions of intermolecular chalcogen bonds in crystal packing of 3a–d: S•••π (3a: 2.4%; 3b: 2.4%), S•••S (3c: less 1%), S•••O (3d: less 1%). The additionally performed DFT calculations, followed by the topological analysis of the electron density distribution within the framework of Bader’s theory (AIM method), confirm the presence of intra-/intermolecular BCB S•••Cl/S•••S in dimer of 3c taken as a model system (solid state geometry). The AIM analysis demonstrates the presence of appropriate bond critical points for these interactions and defines their strength from 0.9 to 2.8 kcal/mol indicating their attractive nature. Full article