Intraoctahedral Distortion Research Articles

Dimensional Reduction of Cs2AgBiBr6 Using Alkyl Ammonium Cations CH3(CH2)nNH3+ (n = 1, 2, 3, and 6) of Varying Chain Lengths and Their Role in Structural and Optoelectronic Properties.

Tuning the dimensionality in halide perovskites provides an opportunity to obtain the properties desired for optoelectronic devices. In this work, we demonstrate the dimensional reduction of 3D halide double-perovskite Cs2AgBiBr6 by systematically introducing alkylammonium organic spacer CH3(CH2)nNH3+ (n = 1, 2, 3, and 6) of varying chain lengths. The single crystals of these materials were grown, and their structures were studied at 23 and -93 °C. The ethylammonium cation led to a formation of a 0D material, whereas all the other three higher alkyl ammonium spacers resulted in two-dimensional materials. The parent material possessed symmetric octahedra, whereas the modified samples led to both inter- and intra-octahedral distortion, thereby reducing the symmetry of constituent octahedra. The reduction in dimensionality led to a blue shift in the optical absorption spectrum. All these low-dimensional materials show excellent stability, and they are employed as absorbers for solar photovoltaics.

Octahedral Distortion and Excitonic Behavior of Cs3Bi2Br9 Halide Perovskite at Low Temperature

The metal halide ionic octahedron, represented as [MX6]n− (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX6]n− octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs3Bi2Br9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi3+ cation within a [BiBr6]3– octahedron due to the Bi3+ 6s2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr6]3– building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs3Bi2Br9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. This work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX6]n− building blocks.

Metal Coordination Sphere Deformation Induced Highly Stokes-Shifted, Ultra Broadband Emission in 2D Hybrid Lead-Bromide Perovskites and Investigation of Its Origin.

Published studies of layered (2D) (100)-oriented hybrid lead-bromide perovskites evidence a correlation between increased inter-octahedral (Pb-Br-Pb) distortions and the appearance of broadband white light emission. However, the impact of distortions within their constituent [PbBr6 ]4- octahedra has yet to be assessed. Herein, we report two new (100)-oriented 2D Pb-Br perovskites, whose structures display unusually high intra-octahedral distortions, whilst retaining minimal inter-octahedral distortions. Using a combination of temperature-dependent, power-dependent and time-resolved photoluminescence spectroscopic measurements, we show that increased intra-octahedral distortion induces exciton localization processes and leads to formation of multiple photoinduced emissive colour centres. Ultimately, this leads to highly Stokes-shifted, ultrabroad white light emission at room temperature.

Probing the Site-Selective Doping in SrSnO3:Eu Oxides and Its Impact on the Crystal and Electronic Structures Using Synchrotron Radiation and DFT Simulations.

The impact of Eu3+ doping at the Sr2+ and Sn4+ sites in SrSnO3 on its structural and electronic properties was studied and correlated with the photocatalytic efficiency. The compounds were synthesized using a modified Pechini method. Refinement of the synchrotron X-ray diffraction (S-XRD) data showed that the samples had an orthorhombic Pbnm symmetry. The incorporation of Eu into the lattice led to increased short- and long-range disorder, inducing additional distortion in the SnO6. XANES measurements revealed that mixed Eu valences (Eu3+ and Eu2+) were present in Eu-doped samples, and DFT calculations confirmed the presence of these ions at Sr2+/Sr4+ sites in the SrSnO3, resulting in changes in the electronic behavior. The catalytic performance toward Remazol yellow dye photodegradation and the catalysts' surface properties were also evaluated. The catalytic efficiency followed the order of Sr(Sn0.99Eu0.01)SnO3 > (Sr0.99Eu0.01)SnO3 > SrSnO3. The order was clearly related to selected-site doping that changed the degree of the inter- and intraoctahedral distortion and the introduction of different Eu midgap states, which apparently favor charge separation upon photoexcitation during photocatalysis. The results shown here are of great importance to the functionalization of SrSnO3 and other perovskite materials by lanthanoid ions, especially Eu3+, for effective applications as photocatalysts.

Intra-octahedral distortion on lamellar potassium niobate K4Nb6O17: a periodic DFT study of structural, electronic and vibrational properties.

Structural, electronic and spectroscopic properties of the anhydrous K4Nb6O17 niobate were investigated in the bulk phase using periodic density functional theory (DFT) calculations with global hybrid (B3LYP) and also including dispersion corrections (B3LYP-D3). The degree of native distortion of different niobium octahedra (here named [NbO6-x], or [NbO6]d) were quantified in terms of the effective coordination number (ECoN) and of other classical descriptors of local deformation and were correlated with the electronic structure. The effect of intrinsic deformation was also examined using the quantum theory of atoms in molecules and crystals (QTAIMC), density of states and charge analyses. The nature of the atom-atom interactions was classified by the ratio of the potential to the kinetic energy density at the bcp (3,-1): |V(rbcp)|/|G(rbcp)|, demonstrating that intraoctahedral Nb-O interactions are well characterized as "transit bond" (between the pure covalent and ionic chemical bonds). The vibrational spectra (infrared and Raman intensities) were fully characterized and discussed, correlating the frequencies with the intraoctahedral distortion.

Disentangling the Effects of Inter- and Intra-octahedral Distortions on the Electronic Structure in Binary Metal Trioxides

Recently, a subclass of binary perovskite-structured metal trioxides, such as WO3 and MoO3, have been propounded for many key optoelectronic applications due to their proper band edge positions and appropriate band gap sizes. Unlike their superclass perovskites, the structure–property relationship for these binary metal trioxides is less apparent, given that they suffer from much larger structural deformities within the octahedra. In this work, by using first-principles density-functional theory calculations and atomistic scale models, we examine the internal and external distortions of WO3 and MoO3 polymorphs. We then compare our results with conventional polyhedral distortion descriptors and finally use a refined data set of different perovskite-structured oxides to establish and demonstrate how these binary metal trioxides operate with a different structure–property relationship from the conventional oxide perovskites.

ChemInform Abstract: New Niobium Selenites, ANbO(SeO3)2 (A: Na, K, Rb, and Cs): Effect of Alkali Metal Cation Size on the Dimensionality and Intraoctahedral Distortion.

AbstractSingle crystals of MNbO(SeO3)2 (M: Na, K, Rb, Cs) are grown by solid state reaction of M2CO3 and Nb2O5 in a reactive SeO2 flux (evacuated silica tubes, 400 °C, 3 d; cooling to 25 °C at a rate of 6 °C/h).

New niobium selenites, ANbO(SeO3)2 (A = Na, K, Rb, and Cs): Effect of alkali metal cation size on the dimensionality and intraoctahedral distortion

Four new alkali metal niobium selenites with both families of second-order Jahn-Teller distortive (SOJT) cations, ANbO(SeO3)2 (A = Na, K, Rb, and Cs), have been synthesized through standard solid state reactions using A2CO3, Nb2O5, and SeO2 in sealed fused silica tubes. Crystal structures of all four materials have been determined by single crystal X-ray diffraction. While NaNbO(SeO3)2 is configured with corner-shared zigzag chains of NbO6 octahedra and SeO3 intrachain connectors, three isostructural ANbO(SeO3)2 (A = K, Rb, and Cs) are arranged with corrugated layers that are composed of NbO6 octahedra and SeO3 trigonal pyramids. More detailed structural investigations indicate that the size and the coordination environment of alkali metal cations particularly affect the backbone geometries and the dimensions of the reported materials. With ANbO(SeO3)2 (A = K, Rb, and Cs), the alkali metal cations in between the layers also influence the extent of octahedral distortions. Full characterizations including thermal analyses, infrared and UV–vis diffuse reflectance spectroscopy, intraoctahedral distortions, and local dipole moment calculations are also presented.

Thermal evolution of the crystal structure of the orthorhombic perovskite LaFeO3

The thermal evolution of the crystal structure of the prototypical orthorhombic perovskite LaFeO3 has been studied in detail by powder neutron diffraction in the temperature range 25<T<1285K. A conventional bond length/bond angle analysis, combined with an analysis in terms of symmetry-adapted modes, allows key aspects of the thermal behavior to be understood. In particular, the largest-amplitude symmetry modes (viz. in-phase and out-of-phase octahedral tilts, and A-site cation displacements) are shown to display relatively ‘normal’ behavior, increasing with decreasing temperature, which contrasts with the anomalous behavior previously shown by the derivative Bi0.5La0.5FeO3. However, an unexpected behavior is seen in the nature of the intra-octahedral distortion, which is used to rationalize the unique occurrence of a temperature dependent crossover of the a and c unit cell metrics in this compound.

New quaternary oxides with both families of second-order Jahn–Teller (SOJT) distortive cations: Solid-state synthesis, structure determination, and characterization of YNbTe2O8 and YNbSe2O8

Two novel quaternary mixed metal tellurite and selenite, YNbTe2O8 and YNbSe2O8, respectively, have been synthesized through standard solid-state reactions using Y2O3, Nb2O5, TeO2 or SeO2 as reagents. Single crystal X-ray and powder neutron diffraction analyses have been utilized to determine the structures of the reported materials. YNbTe2O8 and YNbSe2O8 are isostructural to each other and crystallize in the monoclinic centrosymmetric space group, C2/m (No. 12). Due to the two families of constituent second-order Jahn–Teller (SOJT) distortive cations, i.e., Nb5+ and Te4+/Se4+, local asymmetric environments occur from the three-dimensional frameworks. Intra-octahedral distortions along the local C4 direction and asymmetric trigonal pyramidal coordination moieties generated by stereoactive lone pairs are observed from the NbO6 octahedra and TeO3 (or SeO3) polyhedra, respectively. Thermogravimetric analysis, infrared and UV–vis diffuse reflectance spectroscopies, elemental analysis, out-of-center distortions, dipole moment calculations, and electronic structure calculations for the reported materials are presented.

High-pressure synthesis, structure, phase relation of polar LiNbO3-type ZnTiO3

Ferroelectricity, piezoelectricity, pyroelectricity, and second-order nonlinear optical behavior are technologically important. Because these properties are attributable to the noncentrosymmetric (NCS) structure[1], the search for materials exhibiting such characteristics must begin with a search of NCS materials. Among them, LiNbO3-type (LN-type) compounds with a chemical formula of ABX3 exhibit NSC structures with hexagonal polar space group R3c whose BX6 octahedra three-dimensionally share their corners the same as perovskite-type compounds[2]. In LN-type compounds, the A cation - B cation repulsion directs the spontaneous polarization along c-axis(Fig. 1). Therefore, we might find attractive functional properties by the selection of constituent ions based on their having a naturally occurring polar LN-type structure attributable to the cation-cation repulsion. With the ideas mentioned above, we have investigated the high-pressure synthesis and characterization of novel LN-type oxides such as ZnSnO3, PbNiO3, CdPbO3 as well as known MnMO3 (M = Ti, Sn). Recently, we have successfully synthesized a polar LN-type titanate ZnTiO3 (LN-ZTO) under high pressure and high temperature [3]. The first principles calculation indicates that LN-ZTO is a meta-stable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement reveals that LN-ZTO exhibits greater intra-distortion of the TiO6 in LN-ZTO than that of the SnO6 in LN-type ZnSnO3 (LN-ZSO). The estimated spontaneous polarization are greater than those of LN-ZSO, which is attributed to the great displacement of Ti along c-axis and the greater Born effective charge of Ti (+6.1) than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-ZTO is greater than that of LiNbO3, indicating that LN-ZTO, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-ZTO is 24 times greater than that of LN-ZSO. The findings indicate that the intra-octahedral distortion, spontaneous polarization, and SHG response are caused by the stabilization of the polar LN-type structure and reinforced by the second-order Jahn-Teller effect attributable to the orbital interaction between oxygen ions and d0 ions such as Ti4+. We also discuss the relationship between the intra-distortion of BO6 and polarity in several LN-type oxides.

High-Pressure Synthesis, Crystal Structure, and Phase Stability Relations of a LiNbO3-Type Polar Titanate ZnTiO3and Its Reinforced Polarity by the Second-Order Jahn–Teller Effect

A polar LiNbO3-type (LN-type) titanate ZnTiO3 has been successfully synthesized using ilmenite-type (IL-type) ZnTiO3 under high pressure and high temperature. The first principles calculation indicates that LN-type ZnTiO3 is a metastable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement using synchrotron powder X-ray diffraction data reveals that LN-type ZnTiO3 crystallizes into a hexagonal structure with a polar space group R3c and exhibits greater intradistortion of the TiO6 octahedron in LN-type ZnTiO3 than that of the SnO6 octahedron in LN-type ZnSnO3. The estimated spontaneous polarization (75 μC/cm(2), 88 μC/cm(2)) using the nominal charge and the Born effective charge (BEC) derived from density functional perturbation theory, respectively, are greater than those of ZnSnO3 (59 μC/cm(2), 65 μC/cm(2)), which is strongly attributed to the great displacement of Ti from the centrosymmetric position along the c-axis and the fact that the BEC of Ti (+6.1) is greater than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-type ZnTiO3 is greater than that of LiNbO3 (62 μC/cm(2), 76 μC/cm(2)), indicating that LN-type ZnTiO3, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-type ZnTiO3 is 24 times greater than that of LN-type ZnSnO3. The findings indicate that the intraoctahedral distortion, spontaneous polarization, and the accompanying SHG response are caused by the stabilization of the polar LiNbO3-type structure and reinforced by the second-order Jahn-Teller effect attributable to the orbital interaction between oxygen ions and d(0) ions such as Ti(4+).

Y2MoSe3O12 and Y2MoTe3O12: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment

Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y2MoSe3O12 and Y2MoTe3O12 have been prepared by standard solid-state reactions using Y2O3, MoO3, and SeO2 (or TeO2) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn–Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y2MoSe3O12 shows a three-dimensional framework consisting of YO8, MoO6, and SeO3 groups, Y2MoTe3O12 exhibits a layered structure composed of YO8, MoO4, TeO3, and TeO4 polyhedra. With the Mo6+ cations in Y2MoSe3O12, a C3-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo6+ is away from the oxide ligand linked to a Se4+ cation. The Se4+ and Te4+ cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented.

Dielectric properties of a polar ZnSnO3 with LiNbO3-type structure

The dielectric properties of a polar LiNbO3-type ZnSnO3 synthesized under high-pressure have been investigated with respect to the dielectric permittivity in the relative low frequency range of 10kHz to 1MHz and the SHG response at an optical frequency. The small temperature dependence of dielectric permittivity without anomaly was observed in the temperature range of 300K to 780K. LiNbO3-type ZnSnO3 exhibits the maximum SHG efficiency of approximately 50 times that of quartz. We then compare the structure and SHG response with those of iso-structural LiNbO3 and other known LiNbO3-type oxides. It was found that the magnitude of SHG response is correlated to the magnitude of intra-octahedral distortion, which is effectively brought by the second-order Jahn–Teller effect.

PbMSeO6 (M = Mo and W): New quaternary mixed metal selenites with asymmetric cationic coordination environments

Two new isostructural mixed metal selenites, PbMSeO(6) (M = Mo(6+) or W(6+)), that are only composed of second-order Jahn-Teller (SOJT) distortive cations have been synthesized by standard solid-state reaction techniques using PbO, SeO(2), and MoO(3) (or WO(3)) as reagents. The structures of the reported materials were determined by single-crystal and powder X-ray diffraction. The materials show a three-dimensional framework structure consisting of chains of corner-shared MO(6) octahedra connected by SeO(3) and PbO(8) polyhedra. All of the constituent cations (M(6+), Se(4+), and Pb(2+)) are in distorted environments attributable to second-order Jahn-Teller (SOJT) effects. While the Mo(6+) cations undergo a C(2)-type intraoctahedral distortion toward an edge, the Se(4+) and Pb(2+) cations are in asymmetric coordination environments attributable to their lone pairs. The SeO(3) polyhedra strongly influence the direction of the Mo(6+) intraoctahedral distortion. Infrared spectroscopy, thermogravimetric analysis, the magnitudes of out-of-center distortions, and dipole moment calculations are also presented. Crystal data: PbMoSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8944(6) Å, b = 7.2219(6) Å, c = 10.8294(9) Å, α = 99.751(2)°, β = 99.996(2)°, γ = 90.041(2)°, V = 523.09(8) Å(3), and Z = 2; PbWSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8689(2) Å, b = 7.2398(2) Å, c = 10.9037(3) Å, α = 99.699(4)°, β = 100.348(3)°, γ = 90.139(4)°, V = 525.50(3) Å(3), and Z = 2.

Two New Noncentrosymmetric Polar Oxides: Synthesis, Characterization, Second-Harmonic Generating, and Pyroelectric Measurements on TlSeVO5 and TlTeVO5

Two new noncentrosymmetric (NCS) polar quaternary oxides, TlMVO5 (M = Se4+ or Te4+), have been synthesized by hydrothermal techniques using Tl2CO3, SeO2 (TeO2), and V2O5 as reagents. The structures were determined by single-crystal X-ray diffraction (TlSeVO5, orthorhombic, space group Pna21 (No. 33) with a = 7.1639(15) Å, b = 8.6630(19) Å, c = 7.8946(17) Å, V = 489.95(18) Å3, and Z = 4; TlTeVO5, orthorhombic, space group Pna21 (No. 33) with a = 7.319(3) Å, b = 8.749(4) Å, c = 7.868(3) Å, V = 503.8(4) Å3, Z = 4). The materials exhibit NCS and polar three-dimensional structures consisting of chains of corner shared VO6 octahedra connected by SeO3 (TeO4) and TlO8 polyhedra. The V5+, Se4+ (Te4+), and Tl+ cations are in asymmetric coordination environments attributable to second-order Jahn−Teller (SOJT) effects. The V5+ cations undergo intra-octahedral distortions toward an edge (local C2 direction), whereas the Se4+ (Te4+) and Tl+ cations are in distorted coordination environments attributable to their lone-pair. As the materials are NCS and polar, second-harmonic generating (SHG), ferroelectric, and pyroelectric measurements were performed. The SHG measurements, using 1064 nm radiation, revealed doubling efficiencies of ∼40 × α-SiO2 for both TlSeVO5 and TlTeVO5. Ferroelectric measurements indicated the materials are not “switchable”; that is, the local dipole moment cannot be reversed in the presence of an external electric field. Pyroelectric measurements revealed a total pyroelectric coefficient, p, of −2.9 and −1.9 μC/m2·K, for TlSeVO5 and TlTeVO5, respectively. Infrared, Raman, UV−vis diffuse reflectance spectroscopy, and thermal analyses are also presented.

Mixed‐Metal Tellurites: Synthesis, Structure, and Characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mixed-Metal Tellurites: Synthesis, Structure, and Characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16

Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data: Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) A, b = 7.4541(11) A, c = 6.5649(9) A, beta = 95.636(5) degrees, V = 1576.7(4) A3, and Z = 4; NaNb3Te4O16, monoclinic, space group P2(1)/m (No. 11), with a = 6.6126(13) A, b = 7.4738(15) A, c = 14.034(3) A, beta = 102.98(3) degrees, V = 675.9(3) A3, and Z = 2.

Asymmetric Cationic Coordination Environments in New Oxide Materials: Synthesis and Characterization of Pb4Te6M10O41 (M: Nb5+ or Ta5+).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric Cation Coordination in Oxide Materials: Influence of Lone-Pair Cations on the Intra-octahedral Distortion in d0 Transition Metals

The oxides that contain both a d0 transition metal (Ti4+, Nb5+, W6+, etc.) and a lone-pair cation (Sn2+, Se4+, Te4+, etc.) are examined to investigate the influence of the lone-pair cation on the intra-octahedral distortion of the d0 transition metal. The direction and magnitude of the out-of-center distortion are also examined. When an intra-octahedral distortion is observed, at least one of the d0 transition metal−oxide bonds needs to either be terminal or should link to another d0 transition metal. With respect to the direction of the out-of-center distortion, Ti4+, V5+, and Nb5+ usually displace toward an edge (local C2 direction) or corner (local C4 direction), whereas Mo6+ and W6+ are observed distorting toward an edge (C2) or face (local C3 direction). Finally, the magnitude of the distortion scales as Mo6+ > V5+ > W6+ > Nb5+ > Ta5+ > Ti4+.