Layered double hydroxides with a high layer charge (+0.33 per empirical formula unit) intercalate nitrate ions with the molecular plane of the NO3– ion inclined at ca. 70° to the metal hydroxide layer, which results in a basal spacing of 8.8 Å. Three different N–O bond lengths are observed and yield Cs coordination symmetry. At lower charge (0.165 ≤ x ≤ 0.2), a basal spacing of 8.0 Å is observed, which indicates that the nitrate ion is intercalated with its molecular plane parallel to the metal hydroxide layer (coordination symmetry D3h) in a manner isostructural with carbonate‐intercalated layered double hydroxides. Consequently, crystal chemical considerations predict the layer charge corresponding to the idealized composition of the nitrate‐intercalated phase to be +0.165 per empirical formula unit. The [Mg–Al–NO3]0.165 phase is highly ordered with robust crystal growth along [001] and is stable to hydrothermal treatment, in contrast to the carbonate analogue of the same layer charge. Phases obtained with intermediate layer charge (+0.20 to 0.25 per empirical formula unit) exhibit structural disorder arising out of (i) planar faults and (ii) random interstratification of layers comprising nitrate ions in different orientations.

Manipulating the electron spin with the aid of spin-orbit coupling (SOC) is an indispensable element of spintronics. Electrostatically gating a material with strong SOC results in an effective magnetic field which can in turn be used to govern the electron spin. In this work, we report the existence and electrostatic tunability of Rashba SOC in multilayer InSe. We observed a gate-voltage-tuned crossover from weak localization (WL) to weak antilocalization (WAL) effect in quantum transport studies of InSe, which suggests an increasing SOC strength. Quantitative analyses of magneto-transport studies and energy band diagram calculations provide strong evidence for the predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we attribute the tendency of the SOC strength to saturate at high gate voltages to the increased electronic density of states-induced saturation of the electric field experienced by the electrons in the InSe layer. This explanation of nonlinear gate voltage control of Rashba SOC can be generalized to other electrostatically gated semiconductor nanomaterials in which a similar tendency of spin-orbit length saturation was observed (e.g., nanowire field effect transistors), and is thus of broad implications in spintronics. Identifying and controlling the Rashba SOC in InSe may serve pivotally in devising III-VI semiconductor-based spintronic devices in the future.

The as-precipitated sulfate-intercalated layered double hydroxide of Zn and Al crystallizes in the structure of the 3R1 polytype. On hydrothermal treatment, this 3R1 polytype transforms into the somewhat rare 3H and 3R2 polytypes at different temperatures. Observation of the 3R2 polytype distinct from the 3R1 polytype is evidence for the lack of cation ordering in the [Zn-Al-SO4] system. The layered double hydroxide of Zn and Cr (polytype, 1H) on hydrothermal treatment in mother liquor yields a cation-ordered phase also having the structure of the 1H polytype. Direct evidence of cation ordering is found by the appearance of weak supercell reflections corresponding to a = √3 × a(o) (a(o) is the a parameter of the cation-disordered phase). The same precursor under other conditions yields the cation-disordered 3R1 polytype. In this work, the structures of both the cation-ordered and the cation-disordered phases with similar states of hydration are refined and compared.

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Abstract-Layered double hydroxides (LDH) are extremely important materials for industrial processes and in the environment, and their physical-chemical behavior depends in large part on their hydration state, but the characterization of these hydration effects on their properties are incomplete. The present study was designed to explore the interpolytype transitions induced by variation in the ambient humidity among LDHs. The cooperative behavior of intercalated water molecules resulted in a sudden, single-step, reversible dehydration of the [Zn-Cr-SO 4 ] LDH. The [Zn-Al-SO 4 ] LDH provided an interesting contrast with (1) the coexistence of the end members of the hydration cycle over the 40À20% relative humidity range during the dehydration cycle, and (2) a random interstratified intermediate in the hydration cycle. These observations showed that the [Zn-Al-SO 4 ] LDH offered sites having a range of hydration enthalpies, whereby, at critical levels of hydration (20À40%), the non-uniform swelling of the structure resulted in an interstratified phase. The variation in domain size during reversible hydration was also responsible for the differences observed in the hydration vs. the dehydration pathways. This behavior was attributed to the distortion in the array of hydroxyl ions which departs from hexagonal symmetry on account of cation ordering as shown by structure refinement by the Rietveld method. This distortion was much less in the [Zn-Cr-SO 4 ] LDH, whereby the nearly hexagonal array of hydroxyl ions offered sites of uniform hydration enthalpy for the intercalated water molecules. In this case, all the water molecules experienced the same force of attraction and dehydrated reversibly in a single step. The changes in basal spacing were also accompanied by interpolytype transitions, involving the rigid translations of the metal hydroxide layers relative to one another.

Energetics of CO 2 uptake by layered double hydroxides (LDH) of Mg and Al and their corresponding mixed metal oxides (MMO) of two different compositions (Mg/Al = 2:1 and 3:1) were investigated by gas adsorption calorimetry. The initial adsorption enthalpies for all the LDH and MMO are similar and in the range −90 to −120 kJ/mol, indicating strong chemisorption of CO 2 . However, the differential adsorption enthalpy varies substantially with increasing coverage for different samples. LDH prepared by coprecipitation (both Mg/Al = 2 and 3) and their corresponding MMO exhibit similar CO 2 uptake, which are in the working sorption capacity range (0.6−1 mmol/g), but the one prepared by urea hydrolysis shows poor sorption capacity (0.02−0.35 mmol/g). An integral enthalpy of adsorption of −54 kJ/mol was observed for [Mg−Al−CO 3 ] LDH prepared by urea hydrolysis and −59 kJ/mol and −57 kJ/mol for the ones prepared by coprecipitation with composition 3:1 and 2:1, respectively. Attenuated total reflectance spectroscopy measurements of samples after CO 2 uptake aid in identifying the mode of binding of adsorbed carbonate, which gives information about strength of basic sites. The presence of monodentate carbonate in all samples suggests that strong basic sites are available in LDH and MMO, in agreement with the large exothermic initial adsorption enthalpies observed, indicating strong chemisorption.

The optical response functions and band structures of LiCoO 2 are studied at different levels of approximation, from density functional theory (DFT) in the generalized gradient approximation (GGA) to quasiparticle selfconsistent QSGW (with G for Green's function and W for screened Coulomb interaction) without and with ladder diagrams (QSG Ŵ ) and the Bethe Salpeter Equation (BSE) approach. The QSGW method is found to strongly overestimate the band gap and electron-hole or excitonic effects are found to be important. They lower the quasiparticle gap by only about 11% but the lowest energy peaks in absorption are found to be excitonic in nature. The contributions from different band to band transitions and the relation of excitons to band-to-band transitions are analyzed. The excitons are found to be strongly localized. A comparison to experimental data is presented.

The layered double hydroxides are obtained by the stacking of metal hydroxide layers one above another. The stacking sequence is determined by the molecular symmetry of the intercalated anion. Anions select for those stacking sequences which provide interlayer sites having a local symmetry compatible with their own molecular symmetry. Oxoanions, XO3 n– (X = S, I), are unique in that their molecular symmetry, C 3v , is compatible with two different polytypes of rhombohedral symmetry. The SO3 2– ion selects for the more ubiquitous 3R1 polytype, whereas the IO3 – ion selects for the much rarer 3R2 polytype. Structure refinement shows that neither anion departs significantly from the structure of the free species on intercalation. The higher charge-to-size ratio of the SO3 2– ion compared to the IO3 – ion and its consequent stronger basicity is responsible for the nucleation of the 3R1 polytype, wherein the trigonal prismatic interlayer sites facilitate the superior hydrogen bonding capacity of the SO3 2– ion. The poorer basicity of the IO3 – ion and its consequent poorer proclivity to form hydrogen bonds select for the 3R2 polytype wherein the IO3 – ion is lodged in interlayer sites of octahedral symmetry.