Arrangement Of Cations Research Articles

Structure and cation ordering in La2UO6, Ce2UO6, LaUO4, and CeUO4 by first principles calculations

In the present work, we have used density functional theory (DFT) and DFT+U to investigate the crystal structure and phase stability of four model compounds in the Ln2O3-UO2-UO3 ternary oxide system: La2UO6, Ce2UO6, LaUO4, CeUO4, due to the highly-correlated nature of the f-electrons in uranium. We have considered both hypothetical ordered compounds and compounds in which the cations randomly occupy atomic sites in a fluorite-like lattice. We determined that ordered compounds are stable and are energetically favored compared to disordered configurations, though the ordering tendencies are weak. To model and analyze the structures of these complex oxides, we have used supercells based on a layered atomic model. In the layer model, the supercell is composed of alternating planes of anions and cations. We have considered two different ordering motifs for the cations, namely single species (isoatomic) cation layers versus mixed species cation layers. Energy differences between various ordered cationic arrangements were found to be small. This may have implications regarding radiation stability, since cationic arrangements should be able to change under irradiation with little cost in energy.

Effect of Metal Ions Doping on the Structural and Electrochemical Properties of Olivine LiFePO4

Li ion rechargeable batteries have better performance over the other competitive rechargeable batteries due to their higher operative voltage (around 3-4 v range), high-energy storage capacity, low self-discharge, and high cycleability. For the application in high power devices (various consumer electronic products such as laptop, camcorder, etc.) the discharge capacity of Li ion batteries at higher current rate required is to be improved. As diffusion of lithium ions inside the active material particles is the rate-limiting step of intercalation process, faster Li+ diffusion in the electrode materials could improve the rate capabilities of Li ion batteries. Olive LiFePO4 is a very promising cathode material used in lithium ion batteries, due to its environmental friendliness, high theoretical capacity (170 mAhg-1), low cost of precursors, high reversibility of Li+ insertion/extraction, good thermal stability, and lack of toxicity. In spite of these attractive features, LiFePO4 requires further modifications to overcome limitations such as poor electronic conductivity and slow lithium ion diffusion. In this work we have synthesized olivine LiFe1-xMxPO4 (M = Nb, Yb, Sb, Mg)(LFMPO) powders by chemical synthesis and co-precipitation method. The synthesized powders were used to prepare cathodes for Li ion coin cells. The structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared, Raman spectroscopy, cyclic voltammetry and charge-discharge studies, respectively. The phase pure and crystalline quality of the materials was studied from XRD peaks and their line widths respectively. 7Li magic angle spinning nuclear magnetic resonance were used to compare the cation arrangement in the undoped and doped powders. The cyclic voltammetry of both the cathodes revealed the reversible nature of Li-ion intercalation in the cell. The dopant induced structural and stoichiometric modifications were correlated with the voltage cycling and charge discharge characteristics of these cathode materials.

High temperature induced phase transitions in SrCaCoTeO6 and SrCaNiTeO6 ordered double perovskites

Two new double perovskites SrCaCoTeO6 and SrCaNiTeO6 have been successfully synthesized via the conventional solid state reaction method. The crystal structures and phase transitions of both materials have been investigated using conventional X-ray powder diffraction method at room- and high-temperatures. The Rietveld analysis has shown that both compounds crystallize at room temperature in a primitive monoclinic perovskite-type structure with P21/n (No. 14) space group and 1:1 ordered arrangement of the B-site cations (Co(Ni)/Te). The high temperature analysis has shown that these materials present temperature induced phase transitions following the next phase transition sequence: P21/n(a-a-c+)→I2/m(a-a-c0)→I4/m(a0a0c-)→Fm3¯m(a0a0a0).

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the νas(CH2), (∼2930–2920cm−1), νs(CH2) (∼2860–2850cm−1), 2νas(CH2) (∼5810–5785cm−1), (ν+δ)as(CH2) (∼4340–4330cm−1) and (ν+δ)s(CH2) (∼4270–4250cm−1) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2νas(CH2) (28cm−1) than for νas(CH2) (8cm−1) or νs(CH2) (10cm−1), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH2 bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.

Ammonia-assisted synthesis method for CoTiO3 nanoporous matrix

The theory of an “ammonia fountain” was developed to synthesize a CoTiO3 nanoporous matrix using a modified co-precipitation method at the interface of the aqueous solution and the saturated NH3 atmosphere. On the basis of this theory, for the first time, a new assumption was expanded to show the regular (re)arrangement of metal cations near to the surface of the solution. The morphology of the CoTiO3 phase was observed using SEM. The result indicates the nano-narrow formation of CoTiO3 particles. The size of the particles was calculated at about 27 nm. From the XRD patterns, the formation of cobalt titanate nanoparticles was confirmed.

Finding Rules Governing Layered Architectures of Trifluoroborate Potassium Salts in the Solid State

A set of 15 new crystal structures of aryltrifluoroborate potassium salts (ArBF3–K+), with various substituents at the aromatic ring, is reported. The considered substituents belong to one of three groups: CF3, halogen atoms (F, Cl, Br, I), and alkoxy functions (OMe, OEt, OiPr). All crystals were obtained via solvent evaporation, and the structural features were determined using single-crystal X-ray diffraction methods (including transferred aspherical atom model, TAAM). The resulting layered crystal structures were parametrized, whereas selected ones were additionally characterized computationally (using the periodic DFT approach). The data allowed for formulating basic rules characterizing a given layered structure of the parent phenyltrifluoroborate potassium salt derivative on the basis of the type and location of the aromatic ring substituents. These layered structures can be classified as single or double sheet depending on the mutual arrangement of the potassium cations. The double-sheet type of th...

Structural and spectroscopic studies of alkali-metal exchanged stilbites

The structural, infrared (IR) and Raman spectroscopic properties of alkali-metal exchanged (Na+, K+, Rb+, Cs+) zeolites with the stilbite (STI) framework have been studied by Rietveld analysis of high-resolution synchrotron X-ray powder diffraction data, micro-Raman and synchrotron IR spectroscopy at ambient conditions. Ordered arrangements of the extra-framework cations (EFCs) and H2O molecules were found at the intersection of the 10- and 8-ring channels as well as framework distortions and deformations of the channel system caused by the EFCs distributions. The T(5)–T(5) distances along the chains of the structural building units range from 8.921(1) to 8.979(5) Å and scale with the size of EFCs in Na-, K-, Rb-, Cs-STI. Furthermore, our spectroscopic studies show a systematic increase of characteristic band frequencies for the 4- and 5-ring breathing vibration modes in the far-IR spectral region with the size of the EFCs. The frequencies of the ring vibrational bands in the IR and Raman spectra are very sensitive to the presence of specific EFCS, and framework distortion.

Two in one: switchable ion conductivity and white light emission integrated in an iodoplumbate-based twin chain hybrid crystal.

An iodoplumbate-based hybrid, [C7-Apy][PbI3] (1), where C7-Apy(+) = 1-heptyl-4-aminopyridinium, was prepared using a simple solution process. Three sequential phase transitions occur in the range of 402-443 K. In both the lowest and highest temperature phases, hybrid crystal 1 is composed of discrete [Pb2I6]∞ twin chains surrounded by C7-Apy(+) cations. The connectivity between PbI6 octahedra within a [Pb2I6]∞ twin chain and the arrangement of cations are quite difference between the lowest and highest temperature phases. Hybrid crystal 1 shows switchable ion conductivity due to the structural phase transition and white light emission attributed to the broad band semiconductor emission of the twin chain. The former functionality has potential application in ion conductor devices; the single-phase white light emitter is a useful material in low-cost, easily-made, high-efficiency white light-emitting diodes.

Aサイト層状ペロブスカイト構造酸化物GdBa(Fe<sub>0.5</sub>Mn<sub>0.5</sub>)<sub>2</sub>O<i><sub>x</sub></i>（<i>x</i> = 5, 6）の結晶構造とBサイト陽イオン価数

An A-site layered perovskite GdBa(Fe0.5Mn0.5)2O5 was synthesized and the crystal structure was analyzed. The oxygen vacancies were located in the Gd layers and the valence states of the B-site cations with pyramidal oxygen coordination were Fe3+ and Mn2+. Low-temperature topotactic reaction made the compound a fully oxygenated perovskite GdBa(Fe0.5Mn0.5)2O6 with keeping the cation arrangements. By the oxidation only the valence of Mn increased from 2+ to 4+, while that of Fe remains at 3+.

The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization.

The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization was investigated. A novel intercluster compound, [{(AuLCl)2(μ-OH)}2]3[α-PMo12O40]2·3EtOH (1-PMo12), was obtained as orange-yellow plate crystals in 12.0% yield from a 6 : 1 molar ratio reaction of the monomeric phosphanegold(i) carboxylato complex [Au(RS-pyrrld)(LCl)] (RS-Hpyrrld = RS-2-pyrrolidone-5-carboxylic acid; LCl = tris(4-chlorophenyl)phosphane) in CH2Cl2 with the free acid-form of Keggin polyoxometalate (POM), H3[α-PMo12O40]·14H2O. An EtOH/H2O (5 : 1, v/v) solvent mixture was used. The dimeric cation [{(AuLCl)2(μ-OH)}2](2+) in 1-PMo12 was in a parallel-edge arrangement that was formed by self-assembly through the inter-cationic aurophilic interactions of the μ-OH-bridged dinuclear phosphanegold(i) cation. The POM anion in 1-PMo12 was successfully exchanged with a smaller PF6(-) anion by the use of an anion-exchange resin. POM-free, colorless block crystals of [{(AuLCl)3(μ3-O)}2](PF6)2·4CH2Cl2 (2-PF6) were obtained by vapor diffusion in 14.1% yield. During the synthesis of 2-PF6, a compound with mixed counteranions (one POM and one PF6(-) anion), i.e. [{(AuLCl)4(μ4-O)}]2[α-PMo12O40]PF6 (3-PMo12PF6), was obtained in 66.4% yield. Both products were characterized by elemental analysis, TG/DTA, FT-IR, (31)P{(1)H} NMR, (1)H NMR, and X-ray crystallography. X-ray crystallography revealed that the countercation in 2-PF6 was the dimeric cation of the μ3-O-bridged tris{phosphanegold(i)} species, whereas that in 3-PMo12PF6 consisted of an unusual μ4-O-bridged tetragonal-pyramidal tetrakis{phosphanegold(i)} cation. Therefore, we concluded that the POM anion significantly contributed to the stabilization of these countercations (parallel-edged arrangement in 1-PMo12 and μ4-O-bridged tetragonal-pyramid in 3-PMo12PF6). Moreover, the previously reported yellow crystals of [{(AuLF)2(μ-OH)}2]3[PMo12O40]2·3EtOH (4-PMo12: LF = tris(4-fluoro phenyl)phosphane) were successfully converted to the POM-free crystalline OTf(-) salt [{(AuLF)2(μ-OH)}2](OTf)2·0.5Et2O (4-OTf) by the use of an anion-exchange resin. X-ray crystallography also revealed that the parallel-edge arrangement of the dimeric cation in 4-PMo12 was converted to the crossed-edge arrangement of that in 4-OTf. These results illustrate that the AuOPOM and hydrogen-bonding (C-HOPOM and O-HOPOM) interactions between the phosphanegold(i) cluster cation and the Keggin POM anion in the solid state significantly contribute to the structure, composition, and stability of the phosphane gold(i) cluster cations in 4-PMo12.

Structural insights into the counterion effects on the manganese(III) spin crossover system with hexadentate Schiff-base ligands.

A series of new salts [Mn(5-MeO-sal-N-1,5,8,12)]Y (Y = ClO4 for 1, Y = BF4 for 2, Y = NO3 for 3 and Y = CF3SO3 for 4) based on the six-coordinated mononuclear manganese(iii) Schiff-base complex cation [Mn(5-MeO-sal-N-1,5,8,12)](+), has been investigated to determine the impact of counter anion effects, intramolecular ligand distortion and intermolecular supramolecular structures on the spin crossover (SCO) behavior. The SCO in salt 1 has resulted in a crystallographic observation of the coexistence of high-spin (HS, S = 2) and low-spin (LS, S = 1) manganese(iii) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct manganese centers are both close to the complete HS state. Only one of the two slightly different units undergoes SCO in the temperature range 300-180 K, whereas the other remains in the HS state down to 20 K. For salts 2 and 3, crystal structural analysis indicates change in the anion from ClO4(-) to BF4(-) and NO3(-) was led to the close arrangement of the cations and the stacking between phenyl groups from the ligands. With CF3SO3(-) as the counterion, although the cations and the anions separate clearly in one direction, the close arrangement of cations in other directions precludes the spin transformation of the Mn(iii) cations. Magnetic measurements on 2-4 indicate that the manganese(iii) complex cations remain in the HS state in the temperature range 2-300 K.

Special Collection: Advances in Ultrahigh-Pressure Metamorphism: Tetrahedral boron in natural and synthetic HP/UHP tourmaline: Evidence from Raman spectroscopy, EMPA, and single-crystal XRD

Olenitic tourmaline with high amounts of tetrahedral B (up to 2.53 [4] B pfu) has been synthesized in a piston-cylinder press at 4.0 GPa, 700 °C, and a run duration of 9 days. Crystals are large enough (up to 30 × 150 μm) to allow for reliable and spatially resolved quantification of B by electron microprobe analysis (EMPA), single-crystal X-ray diffraction, and polarized single-crystal Raman spectroscopy. Tourmalines with radial acicular habit are zoned in [4] B-concentration [core: 2.53(25) [4] B pfu; rim: 1.43(15) [4] B pfu], whereas columnar crystals are chemically homogeneous [1.18(15) [4] B pfu]. An amount of 1.4(1) [4] B pfu was found in the columnar tourmaline by single-crystal structure refinement (SREF) ( R = 1.94%). The EMPA identify [T] Si −1 [V,W] O −1 [T] B 1 [V,W] (OH) 1 as the main and [X] □ −1 [T] Si −1 [X] Na 1 [T] B 1 as minor exchange vectors for [4] B-incorporation, which is supported by the SREF. Due to the restricted and well-defined variations in chemistry, Raman bands in the OH-stretching region (3000–3800 cm −1 ) are unambiguously assigned to a specific cation arrangement. We found the sum of the relative integrated intensity ( I rel ) of two low-frequency bands at 3284–3301 cm −1 (ν1) and 3367–3390 cm −1 (ν2) to positively correlate with the [4] B concentrations: [4] B [pfu] = 0.03(1) × [ I rel (ν1) + I rel (ν2)]. Hence, those bands correspond to configurations with mixed Si/B occupancy at the T site. Our semi-quantitative correlation also holds for well-characterized natural [4] B-bearing tourmaline from the Koralpe, Austria. This work shows the potential for Raman spectroscopy as a non-destructive method for the chemical classification of (precious) natural tourmaline, and as a tool to rapidly characterize chemical zonation of tourmalines in thin section.

Au(C9H19N4)](ReO4)2. Synthesis, crystal structure, thermal properties

Acyclic tetraazametal gold(III) perrhenate complex [Au(C9H19N4)](ReO4)2 is synthesized. The 3D crystal structure of the complex is stabilized by weak secondary interactions (N–H…O, C–H…O, С–H…Au hydrogen bonds, and Au…O contacts). The translation sublattice method shows that the motif of the mutual arrangement of cations can be considered to be pseudohexagonal. The product of the thermal decomposition of [Au(C9H19N4)](ReO4)2 in a hydrogen atmosphere is a mixture of nanocrystalline phases (HCP phases based on Re and Au) with the coherent scattering region of 24 nm and 34 nm, respectively.

Crystallographic, Electronic, and Magnetic Properties of Rock Salt Superstructure Sulfide Lu2CrS4 with Jahn–Teller Distortion

A new chromium(II) sulfide, Lu2CrS4, with a novel structure was prepared by a solid-state reaction. The powder X-ray diffraction pattern could be indexed as a tetragonal system, with a = 7.46373(2) Å, c = 22.6338(2) Å, and space group I4̅2d (No. 122). Rietveld analysis of the pattern provided the crystal structure consisting of CrS6 and LuS6 octahedra sharing edges and apexes and revealed a rock salt superstructure with new cation (vacancy) arrangements. The electrical resistivity indicates semiconducting behavior. The magnetic susceptibility and specific heat measurements showed that the Cr ions are in the high-spin d(4) configuration and that their magnetic moments ordered antiferromagnetically at 55 K. The basic antiferromagnetic structure was determined using powder neutron diffraction data at 10 K. The band structure calculations demonstrate that the densities of states of Cr 3d electrons split into two spin-up eg bands because of Jahn-Teller distortion.

Quantitative XRD Analysis of the Structural Changes of Ba-Exchanged Montmorillonite: Effect of an in Situ Hydrous Perturbation

The structural changes along the c axis, of the Ba-exchanged montmorillonite (Swy-2-Ba), under variable relative humidity (% RH), is investigated. In this regard, the arrangement, amount and position of both exchangeable cation and the water molecules in the interlamellar space (IS), are evaluated. This aim is achieved using the X-ray diffraction (XRD) profile modeling approach that consists of comparing experimental and theoretical patterns calculated from structural models. The contributions of the hydration states and the interlayer water amounts, as a function of the % RH, are registered by quantitative XRD investigation. The validated structural models are heterogeneous, suggesting various proportions of layer types at different RH ranges, which means the coexistence of different mixed layer structure MLS packages, exhibiting different proportions of layers with contrasting hydration states. This result is attributed to the orientation of the applied hydration sequence. Indeed, the interlayer water molecule amounts, which led to the appearance of a logic hydration hysteresis, are strongly affected by hydrous perturbation.

Surface structure of organoclays as examined by X-ray photoelectron spectroscopy and molecular dynamics simulations

AbstractOrganoclays are sorbent materials prepared from clays by exchanging inorganic with organic cations. Their properties depend on the loading and conformational structure of the organic cations, but little information is available about the surface structures of organoclays. In this work, X-ray photoelectron spectroscopy (XPS) and classical molecular dynamics (MD) simulations are combined to characterize the external interface of an organoclay prepared from hexadecylpyridinium (HDPy+) and bentonite. The XPS survey spectra show well the varying elemental composition of the surface with increasing amount of surfactant, showing a decreasing contribution of clay-derived elements with increasing organic coverage. The high-resolution C 1s XPS spectra depict sensitively the surface arrangement of the surfactant. In combination with MD simulations, the results implied a monolayer coating for low surfactant coverage and a disordered bilayer arrangement at high surfactant uptakes. Molecular dynamics simulations showed that for very high cation uptake a quasi-paraffin-like configuration is also possible. The combination of experimental and modelling methods yielded congruent information on the molecular-scale arrangement of organic cations at the organoclay surfaces and the controlling mechanisms.

Cation distribution and enhanced surface effects on the temperature-dependent magnetization of as-prepared NiFe2O4 nanoparticles

Nickel ferrite, i.e., NiFe2O4, nanoparticles are synthesized by sol–gel method using urea as a neutralizing agent. The formation of spinel phase and crystal structure of the as-prepared sample is analyzed by X-ray diffraction and transmission electron microscope. In order to confirm phase formation and cation arrangement, room temperature 57Fe Mossbauer spectroscopy is employed. The degree of inversion (i) estimated from the relative peak area is found to be 0.6, which confirms a mixed spinel structure of the as-prepared sample. Zero-field-cooled/field-cooled measurements showed evidence of superparamagnetic behavior associated with the nanosized particles. Hysteresis loop measurements revealed temperature-dependent magnetic properties: The coercive field (H C) decreases with increasing temperature and deviates from the Kneller’s law for ferromagnetic nanostructures; and the saturation magnetization (M s) follows modified Bloch’s law in the temperature range between 25 and 400 K. However, below 25 K, an abrupt increase in magnetization of nanoparticles is observed. In order to understand this behavior, an additional contribution has to be added to the core magnetization to properly fit the data. Hence, a surface correction term to the Bloch’s law is found to describe the temperature dependence of magnetization in the core–shell NiFe2O4 nanoparticles.

Insight for Formation of Oxygen Deficiency in Spinel-Type LiNi0.5Mn1.5O4-δ Using Ab Initio DFT Calculations

Spinel-type LiNi0.5Mn1.5O4 (LNMO) have attracted attention as cathode materials for lithium-ion batteries due to its high-voltage at ~ 4.7 V vs. Li+/Li. LNMO is considered to belong to two different crystal structures such that Ni/Mn ordered P4332 and disordered Fd-3m. Relationship between crystal structures and their electrochemical performances has been experimentally- and computationally- investigated, showing that disordered Fd-3m structure contains oxygen deficiency with reduction of Mn from Mn4+ to Mn3+. Although the presence of Mn3+ improve electronic conductivity, Jahn-Teller distortion and dissolution of Mn occurs. Phase transition from disordered Fd-3m to ordered P4332 occurs with diminish oxygen deficiency by annealing in oxygen atmosphere at 700 ̊C. Understanding the formation mechanism of the oxygen deficiency would be helpful to synthesis aimed crystal structure. However, computational studies with oxygen deficient model are limited so far. In this study, we evaluate the defect formation energies in oxygen deficient LNMO. The Vienna ab initio simulation package (VASP) was utilized with the generalized gradient approximation (GGA-PBEsol) + U and projector-augmented wave (PAW) methods. For the GGA + U calculations, the U values for the d-orbitals of Ni and Mn were set to 6.0 eV and 3.9 eV following relevant previous reports. An energy cutoff of 500 eV and a k-point mesh were chosen such that the product of the number of k-points and the number of atoms in the unit cell was greater than 1000. In the case of disordered Fd-3m structure, we used ‘uniform’ Ni/Mn distribution computationally reported by Lee et al., that is, the highest degree of local cation arrangements within random cation ordering. Coulombic energy was calculated for different 524 structures by Ewald method, the most stable Ni/Mn arrangement was consistent with ‘uniform’ distribution as mentioned above. The calculated lowest oxygen vacancy formation energies in P4332 and Fd-3m show 3.69 eV and 3.38 eV, respectively. Note that vacancy formation energy almost no difference in P4332 among different oxygen vacancy concentrations, whereas, in Fd-3m, vacancy formation energy decreased with increasing oxygen vacancy concentrations. This fact strongly suggests that Fd-3m structure promotes oxygen deficiency. In addition, not only oxygen vacancies type defect but also metal-excess type defect can be present as oxygen defect models. Formation energies for the system contains excess metals in P4332 and Fd-3m lattice show 2.98 eV and 2.58 eV, respectively. Formation energy for metal excess type in Fd-3m became 0.40 eV smaller than that in P4332, in agreement with experimental results that only Fd-3m contains oxygen defects. In addition, these values are lower than oxygen vacancy formation energies. These all finding indicates that metal-excess type oxygen deficiency can be more favorable than oxygen vacancy type oxygen deficiency for LNMO.

First-principles calculation of the bulk photovoltaic effect inKNbO3and (K,Ba)(Ni,Nb)O3−δ

The connection between noncentrosymmetric materials' structure, electronic structure, and bulk photovoltaic performance remains not well understood. In particular, it is still unclear which photovoltaic (PV) mechanism(s) are relevant for the recently demonstrated visible-light ferroelectric photovoltaic (K,Ba)(Ni,Nb)O$_{3-\delta}$. In this paper, we study the bulk photovoltaic effect (BPVE) of (K,Ba)(Ni,Nb)O$_{3-\delta}$ and KNbO$_{3}$ by calculating the shift current from first principles. The effects of structural phase, lattice distortion, oxygen vacancies, cation arrangement, composition, and strain on BPVE are systematically studied. We find that (K,Ba)(Ni,Nb)O$_{3-\delta}$ has a comparable BPVE with that of the broadly explored BiFeO$_{3}$, but for a much lower photon energy. In particular, the Glass coefficient of (K,Ba)(Ni,Nb)O$_{5}$ in a simply layered structure can be as large as 12 times that of BiFeO$_{3}$. Furthermore, the nature of the wavefunctions dictates the eventual shift current yield, which can be significantly affected and engineered by changing the O vacancy location, cation arrangement, and strain. This is not only helpful for understanding other PV mechanisms that relate to the motion of the photocurrent carriers, but also provides guidelines for the design and optimization of PV converters.

Self-Assembling of Tetradecylammonium Chain on Swelling High Charge Micas (Na-Mica-3 and Na-Mica-2): Effect of Alkylammonium Concentration and Mica Layer Charge.

A family of tetradecylammonium micas is synthesized using synthetic swelling micas with high layer charge (Na(n)Si(8-n)Al(n)Mg6F4O20·XH2O, where n = 2 and 3) exchanged with tetradecylammonium cations. The molecular arrangement of the surfactant is elucidated on the basis of XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of micas is investigated by IR/FT, (13)C, (27)Al, and (29)Si MAS NMR. The structural arrangement of the tetradecylammonium cation in the interlayer space of high-charge micas is more sensitive to the effect of the mica layer charge at high concentration. The surfactant arrangement is found to follow the bilayer-paraffin model for all values of layer charge and surfactant concentration. However, at initial concentration below the mica CEC, a lateral monolayer is also observed. The amount of ordered conformation all-trans is directly proportional to the layer charge and surfactant concentration.