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The breaking of inversion symmetry can enhance the multifunctional properties of layered hybrid organic–inorganic perovskites. However, the mechanisms by which inversion symmetry can be broken are not well-understood. Here, we study a series of MnCl4-based 2D perovskites with arylamine cations, namely, (C6H5CxH2xNH3)2MnCl4 (x = 0, 1, 2, 3), for which the x = 0, 1, and 3 members are reported for the first time. The compounds with x = 1, 2, and 3 adopt polar crystal structures to well above room temperature. We argue that the inversion symmetry breaking in these compounds is related to the rotational degree of freedom of the organic cations, which determine the hydrogen bonding pattern that links the organic and inorganic layers. We show that the tilting of MnCl6 octahedra is not the primary mechanism involved in inversion symmetry breaking in these materials. All four compounds show 2D Heisenberg antiferromagnetic behavior. A ferromagnetic component develops in each case below the long-range magnetic ordering temperature of ∼42–46 K due to spin canting., We study a series of MnCl4-based 2D perovskites with arylamine cations: (C6H5CxH2xNH3)2MnCl4 (x = 0, 1, 2, 3). The compounds with x = 1, 2 and 3 adopt polar crystal structures to well above room temperature. The inversion symmetry breaking in these compounds is driven by the rotational degree of freedom of the organic cations, which determine the hydrogen bonding pattern that links the organic and inorganic layers.

Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.

Metastable single crystals of nonstoichiometric Pb1-xTe are obtained by rapid cooling from the melt. The composition and crystallographic morphology are studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. Most single crystals have cubic, pyramidal, or hemispherical shapes with sizes ranging from 50 to 400 mu m. All crystals adopt the same face-centered cubic rock salt structure, and the crystal growth direction is . The bulk part of the rapidly cooled material solidifies in the form of a Te-rich polycrystalline material in which grains are separated by the PbTe-Te eutectic phase. The stabilization of nonstoichiometric Pb1-xTe provides further scope for the optimization of lead telluride-based thermoelectric materials.

Intensive studies have been carried out over the past decade to identify nanostructured thermoelectric materials that allow the efficient conversion of waste heat to electrical power. However, less attention has been paid to the stability of such materials under operating temperatures, typically 400 degrees C or higher. Conventionally nanostructured ceramics tend to undergo grain growth at high temperature, lowering the density of interfaces and raising the thermal conductivity, which is detrimental to device performance. Therefore it is preferable to identify materials with stable nanostructures, for example systems that undergo spontaneous phase separation. Here we investigate PbTe-GeTe alloys, in which spinodal decomposition occurs on initial cooling from above 580 degrees C, forming complex nanostructures consisting of Ge-rich and Pb-rich domains on different size scales. The resulting dense arrangement of interfaces, combined with mass fluctuation associated with Pb-Ge mixing, enhances phonon scattering and strongly reduces the thermal conductivity. Here we focus on the nominal composition Pb0.49Ge0.51Te and show that by tuning the synthesis procedure, we are able to control the pattern of compositional domains and the density of interfaces between them. This allows low lattice thermal conductivities to be maintained even after thermal cycling over the operating temperature range.

The double-layer Aurivillius phase Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 was synthesized by a molten salt method using a K2SO4/Na2SO4 flux. The effect on the crystal structure, morphology, dielectric and magnetic properties of varying the molar ratio of the oxide precursors to salt flux was investigated. Single-phase products with an orthorhombic structure were obtained for oxide to salt ratios of between 1:5 and 1:9, whereas for lower concentrations of salt a pyrochlore impurity phase is found in the products. SEM showed anisotropic plate-like grains, the size of which increases for larger salt ratios. An investigation of the magnetic properties showed the presence of mixed Mn3+ and Mn4+; the unit cell volume of the single-phase products decreases as the proportion of salt increases, which implies a higher proportion of smaller Mn4+ cations. This can be explained by the oxide ion donating properties (oxobasicity) of the molten salt mixture, which produces an oxidizing environment during synthesis. The best dielectric properties are obtained for an oxide to salt ratio of 1:7, exhibiting relaxor ferroelectric behavior. This is also the ratio at which the most pronounced ferromagnetic properties are observed, resulting from double-exchange interactions between Mn3+ and Mn4+ the proportions of which are approximately equal. Pb(0.4)Bi(2.1)La(0.5)Nb(1.7)Mn(0.3)O(9 )synthesized under these conditions thus exhibits optimal multiferroic properties.

(Formula presented.) single crystals are grown with an optimized chemical vapor transport technique using (Formula presented.) as a transport agent (TA). The optimized growth method allows to selectively produce large high-quality single crystals. The method is shown to consistently produce (Formula presented.) crystals of maximum size 8 × 7 × 4 mm with a transport duration of around three weeks. It is found that this method, with (Formula presented.) as TA, is more efficient and simple compared with the commonly used growth techniques reported in literature with HCl gas as TA. The (Formula presented.) crystals have very high quality and their absolute structures are fully determined by simple single-crystal X-ray diffraction. Enantiomeric crystals with either left- or right-handed chiralities are observed. The magnetization and ferromagnetic resonance data show the same magnetic phase diagram as reported earlier.

The double-layer Aurivillius phases Pb1-2xBi1.5+2xLa0.5Nb2-xMnxO9 (x = 0, 0.1, 0.3, and 0.5) were synthesized by a molten salt method using a mixture of K2SO4/Na2SO4. The effect of composition on the structure, morphology and dielectric properties was investigated. X-ray diffraction showed that single-phase samples with a non-polar, orthorhombic A21am structure were obtained for x = 0, 0.1 and 0.3. The unit cell becomes more orthorhombic with increasing x as the degree of distortion of the BO6 octahedra in the perovskite layer increases. Raman spectroscopy showed the typical modes of the orthorhombic double-layer Aurivillius structure and indicated that the La3+ ions prefer to occupy the perovskite A-site, Mn3+ occupies the B-site, and the Pb2+ ions are found in the Bi2O2 layer. The morphology of the samples was probed by scanning electron microscopy, which showed anisotropic, plate-like crystallites that increased in size with increasing x. The dielectric constant significantly increased with x, and the ferroelectric properties became more relaxor-like.

Samples of PbBi2Nb2O9, PbBi1.5La0.5Nb2O9, and PbBi1.5Nd0.5Nb2O9 have been prepared by the molten salt method. The structure, morphology, and electrical properties were investigated. All samples are single-phase and crystallize in an orthorhombic structure with A21am symmetry. Neutron diffraction data indicate that the Ln3+ cations prefer to occupy the perovskite A-site, whereas Pb/Bi occupy the perovskite A-site and the Bi2O2 layer. Changes in unit cell volume are observed on substitution and are attributed to the ionic radii of the Ln3+ cations and also correlated to changes in the B-O bond distances in the BO6 octahedra, which are also observed in IR spectra. SEM images reveal anisotropic plate-like grains, which increase in size with the presence of Ln3+ ions. The ferroelectric transition temperature (Tc) decreases with decreasing degree of BO6 distortion as the influence of the 6s2 lone pair of Bi3+ is diminished. Relaxor ferroelectric behavior is observed with Ln3+ substitution, driven by the disorder of the A-site cations. The room temperature ferroelectric polarization increases with Ln3+ substitution, ascribed to the decreased dielectric loss.

A single-phase sample of the Aurivillius compound Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 was prepared by a molten salt method using K2SO4/Na2SO4 as the flux. The crystal structure, morphology, ferroelectric, and magnetic properties were investigated. Neutron powder diffraction data confirmed a non-centrosymmetric orthorhombic crystal structure with space group A21am and Pb/Bi disorder in the bismuth oxide blocks, Bi/Pb/La disorder on the perovskite A-site, and Nb/Mn disorder on the perovskite B-site. The morphology of the sample showed anisotropic plate-like grains as probed by scanning electron microscopy. The dielectric constant exhibits a transition peak between 600 K and 640 K that depends on frequency, indicating relaxor ferroelectric behavior. Electrical polarization versus applied field loops are unsaturated, with a remnant polarization of 0.43 μC/cm2 at 40 Hz under the maximum electrical field applied of 160 kV/cm. The ferroelectricity originates from the displacement of oxygen atoms in the BO6 octahedra, resulting in a polar structural distortion. Magnetic susceptibility measurements showed the presence of mixed Mn3+ and Mn4+, resulting in short-range ferromagnetic order via double exchange interactions below 33 K. The remnant magnetization (Mr) is 0.01 emu/g at 5 K. This mixed valence of Mn cations is mainly responsible for the high electrical conductivity. Thus, Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 exhibits coexisting ferroelectric and ferromagnetic properties.

We investigate possible mechanisms to induce electric polarization in layered organic-inorganic hybrids. Specifically, we investigate the structural phase transitions of PEA(2)MnCl(4) (PEA = phenethylamine) using temperature dependent single-crystal X-ray diffraction analysis, including the symmetry analysis of the observed space groups. Our results show that PEA(2)MnCl(4) transforms from a high-temperature centrosymmetric structure with space group I4/mmm to a low-temperature polar Pca2(1) phase via an intermediate phase with polar space group Aea2. We study the mechanism responsible for the I4/mmm to Aea2 polar phase transition and find that it is different from previously proposed mechanisms in similar systems. The transition is governed by the opening of a small dihedral angle between the phenyl ring planes of two adjacent PEA molecules, which consequently become crystallographically inequivalent in the Aea2 phase. This molecular rotation induces a significant difference in the lengths of the ethylammonium tails of the two molecules, which coordinate the inorganic layer asymmetrically and are consequently involved in different hydrogen bonding patterns. Consequently, the negatively charged chlorine octahedron that coordinates the Mn(2+)cation deforms. This deformation moves the Mn2+ off-center along the out-of-plane-axis, contributing to the polar nature of the structure. Notably, the polar axis is out-of-plane with respect to the inorganic sheets. This is in contrast to other layered organic-inorganic hybrids as well as conventional layered perovskites, such as the Aurivillius phases, where in-plane polarization is observed. Our findings add to the understanding of possible mechanisms that can induce ferroelectric behavior in layered organic-inorganic hybrids. (C) 2018 Author(s).

High-quality single crystals of perovskite-like (CH

Pentacene crystallizes in a layered structure with a herringbone arrangement within the layers. The electronic properties depend strongly on the stacking of the molecules within the layers (Haddon et al., 2002). We have synthesized four different polymorphs of pentacene, identified by their layer periodicity, d(001): 14.1, 14.4, 15.0 and 15.4 A. Single crystals commonly adopt the 14.1 A structure, whereas all four polymorphs can be synthesized in thin film form, depending on growth conditions. We have identified part of the unit cell parameters of these polymorphs by X-ray and electron diffraction. The 15.0 and 15.4 A polymorphs transform at elevated temperature to the 14.1 and 14.4 A polymorphs, respectively. Using SCLC measurements, we determined the mobility of the 14.1 A polymorph to be 0.2 cm^2/Vs at room temperature., 9 pages, including 6 figures

We investigate the structural, magnetic, and dielectric properties of the organic-inorganic hybrid material CuCl4(C6H5CH2CH2NH3)(2) and demonstrate that spontaneous ferroelectric order sets in below 340 K, which coexists with ferromagnetic ordering below 13 K. We use X-ray diffraction to show that the electric polarization results from the spatial ordering of hydrogen bonds that link the organic block comprised of phenylethylammonium cations to the inorganic copper chloride block. The hydrogen bond ordering is driven by buckling of the corner-linked copper chloride octahedra. Because the magnetic exchange pathways are also determined by this octahedral buckling, a potentially large coupling is induced. Our results imply that such hybrids form a new family of multiferroic materials. KEYWORDS: multiferroic, ferroelectric, ferromagnetic, organic inorganic hybrid, metal-oxide framework

Radical polymerization and copolymerization reactions involving olefin substituted cyclophosphazenes lead to hybrid inorganic-organic polymers and copolymers, which are characterized by a carbon-carbon backbone and pendant phosphazenic groups. The stability of the polymers prepared is related to their structures. The thermal behaviour of poly(cyclophosphazenemethacrylate) (PCPhMA), which appears to possess flame-retardant properties, is compared with that of poly(methylmethacrylate) (PMMA).

Radical polymerization and copolymerization reactions involving olefin substituted cyclophosphazenes lead to hybrid inorganic-organic polymers and copolymers, which are characterized by a carbon-carbon backbone and pendant phosphazenic groups. The stability of the polymers prepared is related to their structures. The thermal behaviour of poly(cyclophosphazenemethacrylate) (PCPhMA), which appears to possess flame-retardant properties, is compared with that of poly(methylmethacrylate) (PMMA).

We have grown the charge-transfer salt of the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the electron donor tetracene using physical vapor transport. The crystal structure was solved by singlecrystal X-ray diffraction and the symmetry was found to be triclinic (space group PT). The 1:1 complex grows by alternating face to face stacking of tetracene and TCNQ molecules. Calculations on the electronic band structure show that the tetracene-TCNQ complex is an indirect band gap semiconductor and provide insight in the conductive properties of tetracene-TCNQ.

We report the effect of air exposure on the electronic properties of pentacene single crystals. Air can diffuse reversibly in and out of the crystals and controls the physical properties. We discern two competing mechanisms that modulate the electronic transport. The presence of oxygen increases the hole conduction, as in dark four O2 molecules introduce one charge carrier. This effect is enhanced by the presence of visible light. Contrarily, water, present in ambient air, is incorporated in the crystal lattice and forms trapping sites for injected charges., Comment: 16 pages, 3 figures

We have obtained a hole mobility for the organic conductor pentacene of 35 cm2/Vs at room temperature increasing to 58 cm2/Vs at 225K. These high mobilities result from a purification process in which 6,13-pentacenequinone was removed by vacuum sublimation. The number of traps is reduced by two orders of magnitude compared with conventional methods. The temperature depandence of the mobility is consistent with the band model for electronic transport., Comment: 5 pages, 3 figures

Pentacene, C22H14, crystallizes in different morphologies characterized by their d(001)-spacings of 14.1, 14.5, 15.0 and 15.4 Angstrom. We have studied the crystal structure of the 14.1 and 14.5 Angstrom d-spacing morphologies grown by vapour transport and from solution. We rnd a close correspondence between the 14.1 Angstrom structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5, 3399-3412] and the 14.5 Angstrom structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14, 705-711]. Single crystals commonly adopt the 14.1 Angstrom d-spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO2 substrates above 350 K preferentially adopt the 14.5 Angstrom d-spacing morphology, with a slightly smaller unit-cell volume.

The misfit layer compounds (MX)(1+x)(TX(2))(m) (with M = Sn, Pb; T = Ti, Nb; X = S, Se; 0.08

The effort to obtain a good crystalline state of delafossite CuCrO2 phase is becoming important along with their potential application and scientific important results. In this paper we report the result of crystal growth and their Magnetic and Electric Capacitance Measurements. We focused on two methods i.e. flux decomposition (FD), and Bi2O3 Flux Growth (FB). The starting materials for FD growth were K2Cr2O7 and CuO taking the advantage of the potassium dichromate’s decomposition. In case of FB flux growth, we should prepare the correct molar ratio for CuCrO2 pellet on the Bi2O3 powder in 1 : 6 ratio. It is found that both methods are possible to obtain crystalline phases along with their specific technical processes to be overcomed. We show that FB method resulted flaky shapes while FD method produced rather bulky morphology. The obtained samples were checked by CAD4 single crystal diffractometer for their lattices and MPMS-SQUID magnetometer for their magnetization for different orientation. We check also the electric capacitance at the range of 5 K to 300 K along c lattice direction. It is found that their single Neel temperature (TN) fall around 25 K. A distinct anisotropy of magnetization profiles shown by its crystal directions and planes. On the other hand the out of plane electric capacitance of Mn doped crystal did not show any transition at the range of 5 K to 300 K.

6,13-Di­hydro­pentacene and pentacene cocrystallize in a ratio of 2:1, i.e. C22H16·0.5C22H14, during vapour transport of commercial pentacene in a gas flow. The crystal structure is monoclinic, space group P21/n, and contains one di­hydro­pentacene mol­ecule and half a pentacene mol­ecule in the asymmetric unit.