One-Step Hydrothermal Synthesis of High-Performance Gas-Sensing Crystals CdIn₂O₄ with Octahedral Shape

Octahedrally shaped CdIn₂O₄ was synthesized in a one-step hydrothermal reaction without any surfactant. These octahedral particles used as an ethanol sensor revealed excellent gas response, which is comparable to the well-known SnO₂-based gas sensors. The octahedral CdIn₂O₄ powder possesses the active {111} facets, which contribute to the higher gas-sensing performance of octahedral CdIn₂O₄ than that of the nanosized CdIn₂O₄ powder obtained by coprecipitation method. The XPS results demonstrated that the CdIn₂O₄ octahedra enclosed by {111} facets provided more oxygen vacancies, resulting in the enhanced performance. The calculation also showed higher surface energies for the {111} orientation, which confirms the mechanism of the enhanced gas-sensing performance of the octahedral particles. The as-formed crystals with controlled morphology provide insights for the designed strategy of high-performance gas-sensing materials, and this synthetic route provides flexibility and selectivity for the deliberate preparation of other functional materials

Synthesis, Structure, and Magnetic Properties of (Tb_1–<i>x</i>Mn_<i>y</i>)MnO_3−δ

Two compounds (Tb_1–<i>x</i>Mn_<i>y</i>)­MnO_3−δ (W1, <i>x</i> = 0.089, <i>y</i> = 0.063; W2, <i>x</i> = 0.122, <i>y</i> = 0.102) have been synthesized by solid-state method and characterized using neutron diffraction and magnetic measurements. They crystallize in space group <i>Pnma</i> at room temperature and <i>Pna2</i>₁ at low temperature. W1 shows a sinusoidal antiferromagnetic order, and W2 shows both sinusoidal and canted commensurate antiferromagnetic orders. The magnetic moments of the commensurate antiferromagnetic order for W2 are antiferromagnetically coupled along the <i>a</i>- and <i>c</i>-axes, and ferromagnetically coupled along the <i>b-</i>axis in the <i>Pna</i>2₁ setting. Strong ferromagnetic response is induced by doping more Mn into the Tb site of (Tb_1–<i>x</i>Mn_<i>y</i>)­MnO<sub>3−δ.</sub

Synthesis and Characterization of a Layered Silicogermanate PKU-22 and Its Topotactic Condensation to a Three-Dimensional <b>STI</b>-type Zeolite

A new layered silicogermanate, PKU-22, was hydrothermally synthesized under fluoride conditions using the tetraethylammonium (TEA⁺) cation as the structure directing agent (SDA). The crystal structure was determined by single crystal X-ray diffraction. Structure analysis reveals that PKU-22 is constructed by <u>sti</u> layers stacking along the [100] direction in an ···AAAA··· manner, with TEA⁺ cations occurring in the interlayer spaces and F^– anions residing within the layer and connecting to Ge atoms, which also act as the charge compensation species. <i>In situ</i> temperature-variable powder X-ray diffraction results indicated that PKU-22 could be transferred into a three-dimensional <b>STI</b>-type zeolite PKU-22a on heating. It is interesting that the TEA⁺ cations remain intact in the structure of the condensed product. Solid-state NMR, inductively coupled plasma atomic emission spectroscopy, thermogravimetric-differential scanning calorimetry, and carbon, hydrogen, and nitrogen elemental analyses were applied to aid the structure analysis of PKU-22 and illustrate its transformation. The scheme of the topotactic condensation of PKU-22 to PKU-22a is proposed

Solid-State ²⁹Si NMR and Neutron-Diffraction Studies of Sr_0.7K_0.3SiO_2.85 Oxide Ion Conductors

K/Na-doped SrSiO₃-based oxide ion conductors were recently reported as promising candidates for low-temperature solid-oxide fuel cells. Sr_0.7K_0.3SiO_2.85, close to the solid-solution limit of Sr_1–<i>x</i>K_<i>x</i>SiO_{3–0.5<i>x</i>}, was characterized by solid-state ²⁹Si NMR spectroscopy and neutron powder diffraction (NPD). Differing with the average structure containing the vacancies stabilized within the isolated Si₃O₉ tetrahedral rings derived from the NPD study, the ²⁹Si NMR data provides new insight into the local defect structure in Sr_0.7K_0.3SiO_2.85. The Q¹-linked tetrahedral Si signal in the ²⁹Si NMR data suggests that the Si₃O₉ tetrahedral rings in the K-doped SrSiO₃ materials were broken, forming Si₃O₈ chains. The Si₃O₈ chains can be stabilized by either bonding with the oxygen atoms of the absorbed lattice water molecules, leading to the Q¹-linked tetrahedral Si, or sharing oxygen atoms with neighboring Si₃O₉ units, which is consistent with the Q³-linked tetrahedral Si signal detected in the ²⁹Si NMR spectra

On the Structure of α‑BiFeO₃

Polycrystalline and monocrystalline α-BiFeO₃ crystals have been synthesized by solid state reaction and flux growth method, respectively. X-ray, neutron, and electron diffraction techniques are used to study the crystallographic and magnetic structure of α-BiFeO_3. The present data show that α-BiFeO₃ crystallizes in space group <i>P</i>1 with <i>a</i> = 0.563 17(1) nm, <i>b</i> = 0.563 84(1) nm, <i>c</i> = 0.563 70(1) nm, α = 59.33(1)°, β = 59.35(1)°, γ = 59.38(1)°, and the magnetic structure of α-BiFeO₃ can be described by space group <i>P</i>1 with magnetic modulation vector in reciprocal space <b>q</b> = 0.0045<b>a</b>* – 0.0045<b>b</b>*, which is the magnetic structure model proposed by I. Sosnowska applied to the new <i>P</i>1 crystal symmetry of α-BiFeO₃

An Open-Framework Aluminophosphite with Face-Sharing AlO₆ Octahedra Dimers and Extra-Large 14-Ring Channels

PKU-25Al, an open-framework aluminophosphite possessing extra-large intersecting 14-ring (14R) channels and a novel Al/P ratio of 9/14, was hydrothermally synthesized using commercially available 4-dimethylaminopyridine (DMAP) as organic structure-directing agents (OSDA). Two types of secondary building units (SBUs), SBU-1 with 6*1 units and racemic SBU-2 composed of two chiral 41 units, are utilized to construct the porous layers with a 4.6.12-net topology and the chains with unprecedented face-sharing AlO₆ octahedra dimers, respectively. Stringing the ABAB stacked layers via the chains would achieve the PKU-25Al framework with a unique topology as well as numerous chiral channel motifs. Meanwhile, the protonated DMAP molecules interact with the inorganic framework through hydrogen bonding and reside in the voids with an exceptional triangular pattern. PKU-25Al is the first aluminophosphite with extra-large channels and enriches the materials chemistry of the open-framework families with exceptive structures

Phase Transitions and Polymerization of C₆H₆–C₆F₆ Cocrystal under Extreme Conditions

Pressure-induced polymerization (PIP) of aromatic molecules can generate saturated carbon nanostructures. As a strongly interacted π–π stacking unit, the C₆H₆–C₆F₆ adduct is widely applied in supramolecular chemistry, and it provides a good preorganization for the PIP. Here we investigated the structural variation of C₆H₆–C₆F₆ cocrystal and the subsequent PIP process under high pressure. Four new molecular-complex phases V, VI, VII, and VIII have been identified and characterized by the in situ Raman, IR, synchrotron X-ray, and neutron diffraction. The phase V is different from the phases observed at low temperature, which has a tilted column structure. Phases VI and VII have a structure similar to phase V. Phase VIII polymerizes irreversibly upon compression above 25 GPa without any catalyst, producing sp³(CH/F)_<i>n</i> materials. The π–π interaction is still dominant below 0.5 GPa but is most likely to be overstepped under further compression, which is important for discussing the supramolecular phase transition and the polymerization process

Topotactic Reduction toward a Noncentrosymmetric Deficient Perovskite Tb_0.50Ca_0.50Mn_0.96O_2.37 with Ordered Mn Vacancies and Piezoelectric Behavior

Low-temperature reduction of perovskite Tb_0.5Ca_0.5MnO_3–<i>x</i> yields novel crystal-structured noncentrosymmetric compound Tb_0.50Ca_0.50Mn_0.96^2.33+O_2.37, which unusually crystallizes in cubic lattice <i>I</i>23 (<i>a</i> ∼ 15.27 Å) based on a 4<i>a</i>_p × 4<i>a</i>_p × 4<i>a</i>_p expansion relative to the simple cubic perovskite unit cell. Rietveld refinements and HAADF-STEM images are used for the structure determination, revealing a rare-typed metal-anion coordination framework which consists of corner-shared tetrahedra and pyramids, and edge-shared bipyramids and octahedra. ²/₆₄ B-site Mn-ordered vacancies are observed for the first time acting as the apex and body center of the <i>I</i> lattice in reduced systems. Room-temperature piezoelectricity is detected, with a quasistatic <i>d</i>₃₃ value of ∼0.32 pC N^–1 and inverse <i>d</i>₃₃ value of ∼10.5 pm V^–1. This phase primarily exhibits antiferromagnetic ordering below <i>T</i>_N ∼ 70 K, with ferromagnetic responses resulted from spin-canting below 40 K. This work provides a new way toward synthesizing unconventional acentric materials, in the absence of second-order Jahn–Teller active “distortion centers”

An Open-Framework Aluminophosphite with Face-Sharing AlO₆ Octahedra Dimers and Extra-Large 14-Ring Channels

PKU-25Al, an open-framework aluminophosphite possessing extra-large intersecting 14-ring (14R) channels and a novel Al/P ratio of 9/14, was hydrothermally synthesized using commercially available 4-dimethylaminopyridine (DMAP) as organic structure-directing agents (OSDA). Two types of secondary building units (SBUs), SBU-1 with 6*1 units and racemic SBU-2 composed of two chiral 41 units, are utilized to construct the porous layers with a 4.6.12-net topology and the chains with unprecedented face-sharing AlO₆ octahedra dimers, respectively. Stringing the ABAB stacked layers via the chains would achieve the PKU-25Al framework with a unique topology as well as numerous chiral channel motifs. Meanwhile, the protonated DMAP molecules interact with the inorganic framework through hydrogen bonding and reside in the voids with an exceptional triangular pattern. PKU-25Al is the first aluminophosphite with extra-large channels and enriches the materials chemistry of the open-framework families with exceptive structures

On the Structure of α‑BiFeO₃

Polycrystalline and monocrystalline α-BiFeO₃ crystals have been synthesized by solid state reaction and flux growth method, respectively. X-ray, neutron, and electron diffraction techniques are used to study the crystallographic and magnetic structure of α-BiFeO_3. The present data show that α-BiFeO₃ crystallizes in space group <i>P</i>1 with <i>a</i> = 0.563 17(1) nm, <i>b</i> = 0.563 84(1) nm, <i>c</i> = 0.563 70(1) nm, α = 59.33(1)°, β = 59.35(1)°, γ = 59.38(1)°, and the magnetic structure of α-BiFeO₃ can be described by space group <i>P</i>1 with magnetic modulation vector in reciprocal space <b>q</b> = 0.0045<b>a</b>* – 0.0045<b>b</b>*, which is the magnetic structure model proposed by I. Sosnowska applied to the new <i>P</i>1 crystal symmetry of α-BiFeO₃