Space Group Ama2 Research Articles

Building High-Density Polar Hybrid Perovskites via Intercalation of Cs+ and Aromatic Diamine for Passive X-ray Detection.

2D organic-inorganic hybrid perovskites (OIHPs) have shown great promise in direct X-ray detection. The development of high-performance passive X-ray detectors in 2D OIHPs calls for an increase in material density while maintaining structural polarity, which is becoming quite challenging. Here, a high-density, polar 2D alternating-cation-intercalated (ACI) perovskite, (4-AP)Cs2Pb2I8 (B, 4-AP = 4-amidinopyridinium), capable of addressing this problem is successfully constructed by introducing heavy Cs+ into the interlayer space of an aromatic Dion-Jacobson (DJ) perovskite (4-AP)PbI4 (A). Through such a DJ-to-ACI design, the newly developed 2D OIHP B not only significantly increases its density to 4.23 g cm-3 (even higher than that of 3D MAPbI3) but also crystallizes in a polar space group (Ama2), which further leads to enhanced X-ray attenuation and an obvious polar photovoltage (1.1 V) under X-ray irradiation. As a result, X-ray detectors fabricated by high-quality single crystals of B exhibit excellent and stable detection performance under self-powered mode with a high sensitivity of 107 μC Gy-1 cm-2 and a low detection limit of 289 nGy s-1. This work provides implications for the future exploration and regulation of novel ACI OIHPs for high-performance photoelectronic devices.

Crystal and electronic structures, transport properties of a ternary tungsten silicophosphide W3Si2P

Here we report a tungsten silicophosphide W3Si2P isostructural and isoelectronic to Mo3Si2P, which was prepared by heating the constituent elements at 1170 °C. It adopts a nonsymmorphic lattice with a-glide symmetry (noncentrosymmetric space group Ama2). The electrical and thermal transport properties were characterized by electrical resistivity, Seebeck effect and thermal conductivity (κ). W3Si2P shows metallic conduction following the Bloch-Grüneisen-Mott model with holes as the main carriers, which is also supported by ab-initio calculations. Electronic and lattice κ make comparable contributions to the thermal conduction at high temperatures, while the electronic component dominates at low temperatures. Electronic-structure calculations reveal that the W 5d orbits govern the bands near the Fermi level, in which 5dx2−y2 orbital electrons take the maximal occupation. As the first genuine ternary compound in W–Si–P family, it might be a novelty playground to probe the underlying electronic physics related to crystallographic symmetry. A tabulation summarizes the compounds in W–Si–P system, and reviews on their structural and physical properties were made to build a comprehensive understanding of this system.

Rational design via dual-site aliovalent substitution leads to an outstanding IR nonlinear optical material with well-balanced comprehensive properties.

The acquisition of a non-centrosymmetric (NCS) structure and achieving a nice trade-off between a large energy gap (E g > 3.5 eV) and a strong second-harmonic generation (SHG) response (d eff > 1.0 × benchmark AgGaS2) are two formidable challenges in the design and development of infrared nonlinear optical (IR-NLO) candidates. In this work, a new quaternary NCS sulfide, SrCdSiS4, has been rationally designed using the centrosymmetric SrGa2S4 as the template via a dual-site aliovalent substitution strategy. SrCdSiS4 crystallizes in the orthorhombic space group Ama2 (no. 40) and features a unique two-dimensional [CdSiS4]2- layer constructed from corner- and edge-sharing [CdS4] and [SiS4] basic building units (BBUs). Remarkably, SrCdSiS4 displays superior IR-NLO comprehensive performances, and this is the first report on an alkaline-earth metal-based IR-NLO material that breaks through the incompatibility between a large E g (>3.5 eV) and a strong phase-matching d eff (>1.0 × AgGaS2). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS4] and [SiS4] BBUs is the main origin of the strong SHG effect and large birefringence. This work not only provides a high-performance IR-NLO candidate, but also offers a feasible chemical design strategy for constructing NCS structures.

Mild solvothermal syntheses and characterizations of five Nb-containing quaternary sulfides

Five quaternary sulfides in the A-Cu/Ag-Nb-S (A = Rb, Cs) family, namely Rb2CuNbS4 (1), Rb2AgNbS4 (2), Cs2AgNbS4 (3), RbCu2NbS4 (4), and CsCu2NbS4 (5) have been synthesized by using Nb powder as the initial material under mild solvothermal conditions. Compounds 1–3 crystallize in space group Fdd and possess one-dimensional (1D) infinite [MNbS4]n2n– (M = Cu for 1; Ag for 2 and 3) anionic chains formed by edge-sharing of [MS4] (M = Cu, Ag) and [NbS4] units. Compounds 4–5 are isostructural and crystallize in space group Ama2. Their structures contain the two-dimensional (2D) [Cu2NbS4]nn– anionic layers, which can be regarded as a further extension of the [CuNbS4]n2n– anionic chains in compounds 1–3. The optical bandgaps and photoelectric response performances of these compounds have also been investigated.

Rational Crystal Structure Design and Nonlinear-Optical Properties of Noncentrosymmetric RbCu2NbS4.

Crystal structure design based on known materials is an efficient strategy for exploring new compounds with evident second-harmonic-generation (SHG) effects. By the introduction of Rb+ ions into the 3D framework of Cu3NbS4, the new compound RbCu2NbS4 (space group Ama2) composed of layers is obtained. The band gap of RbCu2NbS4 is 2.1 eV, indicating that this compound is a semiconductor. Band-structure calculations indicate that the electronic transition mainly occurs from the S 3p/Cu 3d to Nb 4d states. The intercalation of Rb+ ions induces a high degree of local distortion and symmetry reduction, which results in a dipole moment of 11.7 Debye for RbCu2NbS4. RbCu2NbS4 shows a moderate SHG response of 0.33 × AgGaS2 (particle size of 20-41 μm).

A previously unknown cyclic alkanolamine and molecular ranking using the pair distribution function

A new six-membered cyclic alkanolamine with chemical formula C6H15N3O3 was synthesized by the reaction of glycolaldehyde with gaseous ammonia. The molecular structure, characterized by a hexagonal ring of alternating carbon and nitrogen atoms with three hydroxymethyl groups attached to the carbon atoms, could not be unambiguously determined by elemental analysis and 1H/13C/15N NMR. The molecular structure and conformation were further determined using a combination of vibrational spectroscopy (IR and Raman) and real-space pair distribution function (PDF) analysis. The crystal structure was determined ab initio from laboratory X-ray powder diffraction (XRPD) with orthorhombic space group Ama2 (No. 40) and unit-cell parameters a = 12.1054 (2) Å, b = 13.5537 (2) Å and c = 5.20741 (8) Å. Consistent structure models could be obtained by symmetry-independent PDF and PDF-Rietveld co-refinements. Independent local structure refinements indicate that the most likely deviations from the average structure consist of small tilting and translational distortions of hydrogen-bonded molecular stacks. Thermal analysis (TG/DTA) and temperature-dependent XRPD measurements were also performed to determine the thermal behavior.

Structure and magnetic properties of the S = 3/2 zigzag spin chain antiferromagnet BaCoTe2O7

We report a study of the structure and magnetic properties of the S = 3/2 zigzag spin chain compound BaCoTe2O7. Neutron diffraction measurements show that it crystallizes in the noncentrosymmetric space group Ama2 with a canted ↑↑↓↓ spin structure along the quasi-one-dimensional zigzag chain and a moment size of 1.89(2) µB at 2 K. Both magnetic susceptibility and specific heat measurements yield an antiferromagnetic phase transition at TN = 6.2 K. A negative Curie-Weiss temperature, ΘCW = −74.7(2) K, and an empirical frustration parameter, f = ∣ΘCW∣/TN ≈ 12, are obtained by fitting the magnetic susceptibility, indicating antiferromagnetic interactions and strong magnetic frustration. From ultraviolet-visible absorption spectroscopy and first-principles calculations, an indirect band gap of 2.68(2) eV is determined. We propose that the canted zigzag spin chain of BaCoTe2O7 may produce a change in the polarization via the exchange-striction mechanism.

Effect of Pb Substitution in Sr2-xPbxGeSe4 on Crystal Structures and Nonlinear Optical Properties Predicted by DFT Calculations.

We investigated the Sr2-xPbxGeSe4 series from 0 ≤ x ≤ 2 to study the impact of Pb on structure and properties. While the noncentrosymmetric (NCS) compounds γ-Sr2GeSe4 and α-Pb2GeSe4 have already been reported previously, the substitution variants Sr1.31Pb0.69GeSe4 (space group Ama2, a = 10.31220(1) Å, b = 10.39320(1) Å, c = 7.42140(1) Å) and Sr0.19Pb1.81GeSe4 (I4̅3d, a = 14.6177(3) Å) are introduced here for the first time. The experimentally determined optical band gaps decrease as predicted with increasing Pb content from γ-Sr2GeSe4 to Sr1.31Pb0.69GeSe4, Sr0.25Pb1.75GeSe4, and α-Pb2GeSe4 from 2.00, to 1.65, 1.45 and 1.42 eV, respectively. The nonlinear optical (NLO) properties of the orthorhombic compounds γ-Sr2GeSe4 and Sr1.3Pb0.7GeSe4 (approximated with the supercell "Sr3PbGe2Se8") were studied both theoretically, using first-principle calculations, and experimentally. The calculations found the effective nonlinear susceptibility, deff, of γ-Sr2GeSe4 and "Sr3PbGe2Se8" at the static limit to be 10.8 and 8.8 pm V-1, respectively. The experimental deff values of γ-Sr2GeSe4, Sr1.31Pb0.69GeSe4, Sr0.25Pb1.75GeSe4, and α-Pb2GeSe4 were 2.6, 2.3, 0.68, and 0.79 pm V-1, respectively.

Synthesis and characterization of K5Sn2OF11

Abstract The potassium oxidofluoridostannate(IV) fluoride K5Sn2OF11 was synthesized via a solid-state route at T = 300°C in arc-weldeded copper ampoules. It crystallizes in the orthorhombic system in the acentric space group Ama2 (no. 40) with a unit cell volume of V = 2.5727(4) nm3. The cell parameters are a = 1758.3(2), b = 2452.3(2) and c = 596.7(1) pm. As a main structural motif, K5Sn2OF11 exhibits two different kinds of dinuclear [Sn2OF11]5‒ units, which are embedded into a matrix consisting of potassium cations and fluoride anions. The substance was characterized by single-crystal and powder X-ray diffraction, as well as by FT-IR spectroscopy.

BaHgGeSe4 and SrHgGeSe4: Two New Hg-Based Infrared Nonlinear Optical Materials

New practically usable infrared (IR) nonlinear optical (NLO) crystals, especially those suitable for highly efficient pumping of the commercial 1 μm laser, are in urgent demand. However, only a few new IR NLO materials have been grown into bulk crystals and realized IR laser output during the past 20 years due to the extreme difficulty in achieving the coexistence of various strongly correlated properties. In this work, on the basis of the bonding characteristics of the Hg element and an efficient screening strategy for high-performance new crystals, we identified two new Hg-based IR NLO materials, BaHgGeSe4 and SrHgGeSe4. They crystallize in polar space group Ama2 with the distorted HgSe4 and GeSe4 tetrahedra aligned in parallel. They exhibit exceptional balance in terms of all of the preferred properties for practical applications, especially for highly efficient pumping of the commercial 1 μm laser. Their large band gap (∼2.5 eV) can avoid the two-photon absorption of the 1 μm laser and increase the la...

SrCdGeS4 and SrCdGeSe4: Promising Infrared Nonlinear Optical Materials with Congruent-Melting Behavior

The quaternary chalcogenides SrCdGeS4 and SrCdGeSe4 were prepared by high-temperature reactions in the form of single crystals (at 1223 and 1123 K, respectively) or microcrystalline samples (at 1023 K). They adopt non-centrosymmetric structures (orthorhombic, space group Ama2, Z = 4; a = 10.3352(14) A, b = 10.2335(14) A, c = 6.4408(9) A for SrCdGeS4; a = 10.8245(8) A, b = 10.6912(8) A, c = 6.6792(5) A for SrCdGeSe4) consisting of anionic [CdGeCh4]2– layers separated by Sr2+ cations. Although the structure is closely related to the BaZnSiSe4-type, the substitution of Cd for Zn is accompanied by a significant displacement away from an ideal tetrahedral site toward a trigonal pyramidal geometry. Relationships to other similar structures are also elucidated. Large optical band gaps of 2.6 eV for SrCdGeS4 and 1.9 eV for SrCdGeSe4 were deduced from the absorption edges, consistent with the light yellow and red colors, respectively, of crystals of these compounds. Nonlinear optical measurements on powder samples...

Crystal structure of LnTe3, where Ln = La, Ho

LnTe3 (Ln = La, Ho) single crystals are produced by the interaction of elementary compounds in an alkali halide melt. The structures of the obtained compounds are determined by single crystal X-ray diffraction. It is found that LaTe3 crystallizes in the space group Ama2 with the following parameters: a = 4.4195(2) A, b = 26.2644(11) A, c = 4.4028(2) A. As for HoTe3, the space group Cmcm with the following parameters a = 4.2994(18) A, b = 25.393(10) A, c = 4.3021(17) A is determined.

K2[B3O3(OH)5]: A new deep-UV nonlinear optical crystal with isolated [B3O3(OH)5]2- anionic groups

A new noncentrosymmetric material, namely, K2[B3O3(OH)5] has been obtained by conventional solution reaction. It crystallizes in the orthorhombic space group Ama2 (no. 40). In the structure of K2[B3O3(OH)5], the BO2(OH) triangles and BO2(OH)2 tetrahedra are linked via sharing corners forming the isolated [B3O3(OH)5]2- anionic groups with no dangling bonds in oxygen atoms. And K2[B3O3(OH)5] is the first synthetic noncentrosymmetric borates with [B3O3(OH)5]2- anionic groups. Powder second-harmonic generation (SHG) using the Kurtz−Perry technique showed that K2[B3O3(OH)5] is type I phase-matchable, and the measured SHG coefficient is 0.32 times that of KH2PO4. The UV transmittance spectroscopy measurement indicated that the UV absorption edge was below 200 nm, suggesting that K2[B3O3(OH)5] might be a promising deep-UV nonlinear optical material. Band structure and optical property calculations based on DFT methods were also performed.

Superconductivity and unexpected chemistry of germanium hydrides under pressure

Following the idea that hydrogen-rich compounds might be high-T$_c$ superconductors at high pressures, and the very recent breakthrough in predicting and synthesizing hydrogen sulfide with record-high T$_c$ = 203 K, ab initio evolutionary algorithm for crystal structure prediction was employed to find stable germanium hydrides. In addition to the earlier structure of germane with space group Ama2, we propose a new C2/m structure, which is energetically more favorable at pressures above 278 GPa (with inclusion of zero point energy). Our calculations indicate metallicity of the new C2/m phase of germane with T$_c$ = 67 K at 280 GPa. Germane is found to exhibit thermodynamic instability to decomposition to hydrogen and the new compound Ge$_3$H$_{11}$ at pressures above 300 GPa. Ge$_3$H$_{11}$ with space group I$\bar{4}$m2 is found to become stable at above 285 GPa with T$_c$ = 43 K. We find that the pressure-induced phase stability of germanium hydrides is distinct from its analogous isoelectronic systems, e.g., Si-hydrides and Sn-hydrides. Superconductivity stems from large electron-phonon coupling associated with the wagging, bending and stretching intermediate-frequency modes derived mainly from hydrogen.

Noncentrosymmetric chalcogenides BaZnSiSe4 and BaZnGeSe4 featuring one-dimensional structures

Abstract The two quaternary tetrel-containing selenides BaZnTtSe4 (Tt = Si, Ge) have been prepared by reactions of BaSe, ZnSe, Tt, and Se at 1023 K. They adopt noncentrosymmetric structures (orthorhombic, space group Ama2, Z = 4; a = 11.3055(8) A, b = 11.2344(7) A, c = 6.1994(4) A for BaZnSiSe4; a = 11.3255(6) A, b = 11.2527(6) A, c = 6.2917(3) A for BaZnGeSe4) that are of a new type consisting of one-dimensional chains of edge-sharing tetrahedra alternately centred by Zn and Tt atoms, with Ba cations separating the chains. The structure type is closely related to Sr2SnSe4 and NaEuAsS4. Large optical band gaps of 2.71(2) eV for BaZnSiSe4 and 2.46(2) eV for BaZnGeSe4, as deduced from UV–vis–NIR diffuse reflectance spectra, are consistent with the yellow or orange colour of the crystals. Nonlinear optical measurements on powder samples revealed that BaZnGeSe4 exhibited good second harmonic generation signals and type-I phase-matching behaviour using 2090 nm as the fundamental laser wavelength.

Blue-green tunable color of Ce(3+)/Tb(3+) coactivated NaBa3La3Si6O20 phosphor via energy transfer.

A series of color tunable phosphors NaBa3La3Si6O20:Ce3+, Tb3+ were synthesized via the high-temperature solid-state method. NaBa3La3Si6O20 crystallizes in noncentrosymmetric space group Ama2 with the cell parameters of a = 14.9226(4) Å, b = 24.5215(5) Å and c = 5.6241(2) Å by the Rietveld refinement method. The Ce3+ ions doped NaBa3La3Si6O20 phosphors have a strong absorption band from 260 to 360 nm and show near ultraviolet emission light centered at 378 nm. The Ce3+ and Tb3+ ions coactivated phosphors exhibit color tunable emission light from deep blue to green by adjusting the concentration of the Tb3+ ions. An energy transfer of Ce3+ → Tb3+ investigated by the photoluminescence properties and lifetime decay, is demonstrated to be dipole–quadrupole interaction. These results indicate the NaBa3La3Si6O20:Ce3+, Tb3+ phosphors can be considered as potential candidates for blue-green components for white light emitting diodes.

Hydrothermal synthesis, structure, and property characterization of rare earth silicate compounds: NaBa3Ln3Si6O20 (Ln = Y, Nd, Sm, Eu, Gd)

A series of new lanthanide (Ln) silicates have been synthesized using high temperature hydrothermal techniques, and structurally characterized using single crystal and powder X-ray diffraction. The compounds have the general formula NaBa3Ln3Si6O20 (Ln = Y, Nd, Sm, Eu, Gd), and crystallize in the space group Ama2 (No.40). As a representative example, the unit cell parameters of NaBa3Gd3Si6O20 are a = 14.731(3) Å, b = 23.864(5) Å, c = 5.5449(11) Å and Z = 4. The title compounds adopt a three dimensional polar acentric framework made of Ln–O–Si bonding. The framework is comprised of LnO8 and LnO7 units forming edge-sharing infinite chains along the c-axis. These oxy-bridged infinite chains are also linked by [Si4O13] tetrasilicate and [Si2O7] disilicate units to form the three-dimensional framework structure, with Ba2+ and Na+ cations residing inside channels of the framework. The polarity in the structure is imparted by the unusual tetrasilicate arrangement. The luminescence and magnetic properties were investigated on selected compounds. The temperature dependent magnetic susceptibility measurements on the Nd, Sm, and Gd derivatives reveal a Curie–Weiss behavior with an antiferromagnetic coupling parameter. For the Eu-derivative, the temperature dependent magnetic susceptibility deviates significantly from Curie–Weiss behavior. Luminescence properties of NaBa3Eu3Si6O20 and NaBa3Sm3Si6O20 compounds exhibited the characteristic transitions of Eu3+ (5D0 → 7FJ, J = 0–4) and Sm3+ (4G5/2 → 6HJ, J = 5/2, 7/2), respectively, leading to strong visible red and orange emissions, respectively.

Two New Crystals in Li(m)Cs(n)B(m+n)O2(m+n) (m + n = 5, 7; m > n) Series: Noncentrosymmetric Li5Cs2B7O14 and Centrosymmetric Li4CsB5O10.

With the introduction of an alkali metal into the B-O framework, two new alkali metal borate crystals, Li5Cs2B7O14 and Li4CsB5O10, have been obtained for the first time. Both compounds obey a general formula of Li(m)Cs(n)B(m+n)O2(m+n) (m + n = 5, 7; m > n). The two crystals have different three-dimensional (3D) framework structures composed by LiOn (n = 4, 5), CsO10, BO3, and BO4 units. Li5Cs2B7O14 crystallizes into the polar and noncentrosymmetric space group Ama2, while Li4CsB5O10 belongs to the nonpolar and centrosymmetric space group P21/c. Detailed structure comparison analysis indicates that the different arrangements of the anionic groups in Li(m)Cs(7-m)B7O14 (m = 4, 5) and Li(m)Cs(5-m)B5O10 (m = 3, 4) may arise from the cation size effects, bond-valence requirements, and differences of coordination environment. In addition, in order to get better understandings of electronic structures and linear optical properties, we also carried out first-principle theoretical studies.

Computationally Assisted (Solid-State Density Functional Theory) Structural (X-ray) and Vibrational Spectroscopy (FT-IR, FT-RS, TDs-THz) Characterization of the Cardiovascular Drug Lacidipine

The structural properties of a second-generation dihydropyridine calcium antagonist, lacidipine, were explored by combining low-temperature X-ray diffraction with optical vibrational spectroscopy and periodic density functional theory (PBC DFT) calculations. Crystallographic analysis cannot discriminate between two possible molecular symmetries in crystals made of pure lacipidine: the space group Ama2, where the lacipidine molecule lies on mirror symmetry, or a Cc space group with distorted lacipidine molecules. Intermolecular interactions analysis reveals an infinite net of moderate-strength N–H···O hydrogen-bonds, which link the molecular units toward the crystallographic b-axis. Weak interactions were identified, revealing their role in stabilization of the crystal structure. The vibrational dynamics of lacidipine was thoroughly explored by combining infrared and Raman spectroscopy in the middle- and low-wavenumber range. The given interpretation was fully supported by state-of-the-art solid-state dens...

Hydrothermal growth of lanthanide borosilicates: a useful approach to new acentric crystals including a derivative of cappelenite.

The reaction of barium borosilicate glasses in hydrothermal fluids with NaOH mineralizer at ca. 600-650 °C in the presence of various sources of Eu(3+) ions leads to a new series of noncentrosymmetric single crystals characterized by single-crystal X-ray diffraction. Under three slightly different reaction modifications, three new Eu(3+)-containing noncentrosymmetric single crystals were isolated and characterized. Using a barium borosolicate glass with Eu(2)O(3) added to the reaction mixture led to NaBaEuSi(3)O(9) (1), which crystallizes in the noncentrosymmetric orthorhombic space group P2(1)2(1)2(1) with unit cell parameters a = 5.6373(11) Å, b = 11.483(2) Å, and c = 12.535(2) Å and consists of Eu(3+) ions linked by Si(3)O(9)(6-) rings. Using a similar glass feedstock with Eu(3+) included in the starting glass composition led to the compound NaBa(3)Eu(3)Si(6)O(20) (2), which was determined in the noncentrosymmetric polar space group Ama2 with unit cell parameters a = 14.777(3) Å, b = 23.926(5) Å, and c = 5.5533(11) Å. It is constructed of individual islands of Si(4)O(13)(10-) and lone Si(2)O(7)(6-) building fragments. Finally, use of the Eu-containing glass along with additional Eu(2)O(3) led to the compound BaEu(6)(Si(3)B(6)O(24))(OH)2 (3), which crystallizes in the polar space group P6mm with a = 10.8074(15) Å and c = 4.7296(9) Å. It is related to the rare and poorly understood mineral cappelenite Ba(Y,RE)(6)(Si(3)B(6)O(24))F(2) and contains six-membered tetrahedral borate rings linked by silicate tetrahedra. The high percentage of noncentrosymmetric crystals obtained from of a simple borosilicate glass starting material, along with various straightforward chemical additives, suggests strongly that many more noncentrosymmetric crystals can be isolated from this general system.