13 research outputs found
Hydrothermal Synthesis of Open-Framework Borophosphates with Tunable Micropore Sizes, Crystal Morphologies, and Thermal Stabilities
Thermal
stabilities of zeolitic frameworks are important parameters
for many applications. Two decades of research have produced only
a very small number of zeolitic borophosphates such as Na<sub>2</sub>[VOĀ(B<sub>2</sub>O)Ā(PO<sub>4</sub>)<sub>2</sub>(HBO<sub>3</sub>)]Ā·<i>x</i>H<sub>2</sub>O (<i>x</i> <b> ā </b> 2.92) (denoted as <b>B</b><sub><b>3</b></sub><b>P</b><sub><b>2</b></sub>), which shows the onset dehydration and
a complete decomposition at 200 and 400 Ā°C, respectively. In
order to enhance thermal stabilities of borophosphate frameworks,
a water-deficient hydrothermal route with phosphoric acid as the sole
solvent has been developed and led to controlled syntheses of <b>B</b><sub><b>3</b></sub><b>P</b><sub><b>2</b></sub> and a new vanadium borophosphate, K<sub>1.33</sub>Na<sub>0.67</sub>[VOĀ(B<sub>2</sub>O)Ā(PO<sub>4</sub>)<sub>2</sub>(HPO<sub>4</sub>)]Ā·<i>x</i>H<sub>2</sub>O (<i>x</i> <b> ā </b> 1.63) (denoted as <b>B</b><sub><b>2</b></sub><b>P</b><sub><b>3</b></sub>). The latter is the first-ever borophosphate
possessing the zeolite RHO-type net and is characterized by superlarge
spherical cages, including 16-ring and 8-ring channels along the axes
and 12-ring channels along the diagonals of the cubic cell. The new
compound <b>B</b><sub><b>2</b></sub><b>P</b><sub><b>3</b></sub> has larger structural cages and higher thermal
stability than <b>B</b><sub><b>3</b></sub><b>P</b><sub><b>2</b></sub>, where the enhanced thermal stability is
attributable to different bonding arising from the substitution of
[BO<sub>2</sub>(OH)] by [PO<sub>3</sub>(OH)] in the framework. This
is the first demonstration that the micropore size, crystal morphology,
and thermal stability of zeolitic borophosphates can be tuned by changing
the fundamental building units of their frameworks via adjusting the
B/P ratios in the starting materials
Multiple Fluorine-Substituted Phosphate Germanium Fluorides and Their Thermal Stabilities
Anhydrous compounds
are crucially important for many technological applications, such
as achieving high performance in lithium/sodium cells, but are often
challenging to synthesize under hydrothermal conditions. Herein we
report that a modified solvo-/hydro-fluorothermal method with fluoride-rich
and water-deficient condition is highly effective for synthesizing
anhydrous compounds by the replacement of hydroxyl groups and water
molecules with fluorine. Two anhydrous phosphate germanium fluorides,
namely, Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] and K<sub>4</sub>[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)], with chainlike
structures involving multiple fluorine substitutions, were synthesized
using the modified solvo-/hydro-fluorothermal method. The crystal
structure of Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] is constructed
by the common single chains <sub>ā</sub><sup>1</sup>{[GeF<sub>4</sub>(PO<sub>4</sub>)]<sup>3ā</sup>} built from alternating
GeO<sub>2</sub>F<sub>4</sub> octahedra and PO<sub>4</sub> tetrahedra.
For K<sub>4</sub>[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)], it
takes the same single chain in Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] as the backbone but has additional flanking GeOF<sub>5</sub> octahedra via an O-corner of the PO<sub>4</sub> groups, resulting
in a dendrite zigzag single chain <sub>ā</sub><sup>1</sup>{[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)]<sup>4ā</sup>}. The multiple
fluorine substitutions in these compounds not only force them to adopt
the low-dimensional structures because of the ātailor effectā
but also improve their thermal stabilities. The thermal behavior of
Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] was investigated by
an in situ powder X-ray diffraction experiment from room temperature
to 700 Ā°C. The modified solvo-/hydro-fluorothermal method is
also shown to be effective in producing the most germanium-rich compounds
in the germanophosphate system
Multiple Fluorine-Substituted Phosphate Germanium Fluorides and Their Thermal Stabilities
Anhydrous compounds
are crucially important for many technological applications, such
as achieving high performance in lithium/sodium cells, but are often
challenging to synthesize under hydrothermal conditions. Herein we
report that a modified solvo-/hydro-fluorothermal method with fluoride-rich
and water-deficient condition is highly effective for synthesizing
anhydrous compounds by the replacement of hydroxyl groups and water
molecules with fluorine. Two anhydrous phosphate germanium fluorides,
namely, Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] and K<sub>4</sub>[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)], with chainlike
structures involving multiple fluorine substitutions, were synthesized
using the modified solvo-/hydro-fluorothermal method. The crystal
structure of Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] is constructed
by the common single chains <sub>ā</sub><sup>1</sup>{[GeF<sub>4</sub>(PO<sub>4</sub>)]<sup>3ā</sup>} built from alternating
GeO<sub>2</sub>F<sub>4</sub> octahedra and PO<sub>4</sub> tetrahedra.
For K<sub>4</sub>[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)], it
takes the same single chain in Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] as the backbone but has additional flanking GeOF<sub>5</sub> octahedra via an O-corner of the PO<sub>4</sub> groups, resulting
in a dendrite zigzag single chain <sub>ā</sub><sup>1</sup>{[Ge<sub>2</sub>F<sub>9</sub>(PO<sub>4</sub>)]<sup>4ā</sup>}. The multiple
fluorine substitutions in these compounds not only force them to adopt
the low-dimensional structures because of the ātailor effectā
but also improve their thermal stabilities. The thermal behavior of
Na<sub>3</sub>[GeF<sub>4</sub>(PO<sub>4</sub>)] was investigated by
an in situ powder X-ray diffraction experiment from room temperature
to 700 Ā°C. The modified solvo-/hydro-fluorothermal method is
also shown to be effective in producing the most germanium-rich compounds
in the germanophosphate system
Two Isotypic Transition Metal Germanophosphates <i>M</i><sup>II</sup><sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>[Ge(OH)<sub>2</sub>(HPO<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>] (<i>M</i><sup>II</sup> = Fe, Co): Synthesis, Structure, MoĢssbauer Spectroscopy, and Magnetic Properties
Synthetic, structural, thermogravimetric, MoĢssbauer
spectroscopic, and magnetic studies were performed on two new isotypic
germanophosphates, <i>M</i><sup>II</sup><sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>[GeĀ(OH)<sub>2</sub>(HPO<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>] (<i>M</i><sup>II</sup> =
Fe, Co), which have been prepared under hydro-/solvo-thermal conditions.
Their crystal structures, determined from single crystal data, are
built from zigzag chains of <i>M</i><sup>II</sup>O<sub>6</sub>-octahedra sharing either trans or skew edges interconnected by [GeP<sub>4</sub>O<sub>14</sub>(OH)<sub>4</sub>]<sup>8ā</sup> germanophosphate
pentamers to form three-dimensional neutral framework structure. The
edge-sharing <i>M</i><sup>II</sup>O<sub>6</sub>-octahedral
chains lead to interesting magnetic properties. These two germanophosphates
exhibit a paramagnetic to antiferromagnetic transition at low temperatures.
Additionally, two antiferromagnetic ordering transitions at around
8 and 6 K were observed for cobalt compound while only one at 19 K
for the iron compound. Low-dimensional magnetic correlations within
the octahedral chains are also observed. The divalent state of Fe
in the iron compound determined from the MoĢssbauer study and
the isothermal magnetization as well as thermal analyses are discussed
Two Isotypic Transition Metal Germanophosphates <i>M</i><sup>II</sup><sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>[Ge(OH)<sub>2</sub>(HPO<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>] (<i>M</i><sup>II</sup> = Fe, Co): Synthesis, Structure, MoĢssbauer Spectroscopy, and Magnetic Properties
Synthetic, structural, thermogravimetric, MoĢssbauer
spectroscopic, and magnetic studies were performed on two new isotypic
germanophosphates, <i>M</i><sup>II</sup><sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>[GeĀ(OH)<sub>2</sub>(HPO<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>] (<i>M</i><sup>II</sup> =
Fe, Co), which have been prepared under hydro-/solvo-thermal conditions.
Their crystal structures, determined from single crystal data, are
built from zigzag chains of <i>M</i><sup>II</sup>O<sub>6</sub>-octahedra sharing either trans or skew edges interconnected by [GeP<sub>4</sub>O<sub>14</sub>(OH)<sub>4</sub>]<sup>8ā</sup> germanophosphate
pentamers to form three-dimensional neutral framework structure. The
edge-sharing <i>M</i><sup>II</sup>O<sub>6</sub>-octahedral
chains lead to interesting magnetic properties. These two germanophosphates
exhibit a paramagnetic to antiferromagnetic transition at low temperatures.
Additionally, two antiferromagnetic ordering transitions at around
8 and 6 K were observed for cobalt compound while only one at 19 K
for the iron compound. Low-dimensional magnetic correlations within
the octahedral chains are also observed. The divalent state of Fe
in the iron compound determined from the MoĢssbauer study and
the isothermal magnetization as well as thermal analyses are discussed
Dimensional Reduction From 2D Layer to 1D Band for Germanophosphates Induced by the āTailor Effectā of Fluoride
The ātailor effectā
of fluoride, exclusively as a terminal rather than a bridge, was applied
successfully to design low-dimensional structures in the system of
transition metal germanophosphates for the first time. Two series
of new compounds with low-dimensional structures are reported herein.
KĀ[<i>M</i><sup>II</sup>GeĀ(OH)<sub>2</sub>(H<sub>0.5</sub>PO<sub>4</sub>)<sub>2</sub>] (<i>M</i> = Fe, Co) possess
flat layered structures built from single chains of edge-sharing <i>M</i><sup>II</sup>O<sub>6</sub> and GeO<sub>6</sub> octahedra
interconnected by HPO<sub>4</sub> tetrahedra. Their fluorinated derivatives,
K<sub>4</sub>[<i>M</i><sup>II</sup>Ge<sub>2</sub>F<sub>2</sub>(OH)<sub>2</sub>Ā(PO<sub>4</sub>)<sub>2</sub>(HPO<sub>4</sub>)<sub>2</sub>]Ā·2H<sub>2</sub>O (M = Fe, Co), exhibit band structures
of two four-membered ring germanium phosphate single chains sandwiched
by M<sup>II</sup>O<sub>6</sub> octahedra via corner-sharing. Both
of these structures contain anionic chains of the condensation of
four-membered rings built from alternating GeO<sub>4</sub>Ī¦<sub>2</sub> (Ī¦ = F, OH) octahedra and PO<sub>4</sub> tetrahedra
via sharing common GeO<sub>4</sub>Ī¦<sub>2</sub> (Ī¦ = F,
OH) octahedra, the topology of which is the same as that of the mineral
kroĢhnkite [Na<sub>2</sub>CuĀ(SO<sub>4</sub>)<sub>2</sub>Ā·2H<sub>2</sub>O]. Note that the switch from the two-dimensional layered
structure to the one-dimensional band structure was performed simply
by the addition of a small amount of KFĀ·2H<sub>2</sub>O to the
reaction mixture. This structural alteration arises from the incorporation
of one terminal F atom to the coordination sphere of Ge, which breaks
the linkage between the transition metal and germanium octahedra in
the layer to form the band structure
Toward Understanding the Lithium Transport Mechanism in Garnet-type Solid Electrolytes: Li<sup>+</sup> Ion Exchanges and Their Mobility at Octahedral/Tetrahedral Sites
The
cubic garnet-type solid electrolyte Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> with aliovalent doping exhibits a high
ionic conductivity, reaching up to ā¼10<sup>ā3</sup> S/cm
at room temperature. Fully understanding the Li<sup>+</sup> transport
mechanism including Li<sup>+</sup> mobility at different sites is
a key topic in this field, and Li<sub>7ā2<i>x</i>ā3<i>y</i></sub>Al<sub><i>y</i></sub>La<sub>3</sub>Zr<sub>2ā<i>x</i></sub>W<sub><i>x</i></sub>O<sub>12</sub> (0 ā¤ <i>x</i> ā¤ 1) are
selected as target electrolytes. X-ray and neutron diffraction as
well as ac impedance results show that a low amount of aliovalent
substitution of Zr with W does not obviously affect the crystal structure
and the activation energy of Li<sup>+</sup> ion jumping, but it does
noticeably vary the distribution of Li<sup>+</sup> ions, electrostatic
attraction/repulsion, and crystal defects, which increase the lithium
jump rate and the creation energy of mobile Li<sup>+</sup> ions. For
the first time, high-resolution NMR results show evidence that the
24d, 96h, and 48g sites can be well-resolved. In addition, ionic exchange
between the 24d and 96h sites is clearly observed, demonstrating a
lithium transport route of 24dā96hā48gā96hā24d.
The lithium mobility at the 24d sites is found to dominate the total
ionic conductivity of the samples, with diffusion coefficients of
10<sup>ā9</sup> m<sup>2</sup> s<sup>ā1</sup> and 10<sup>ā12</sup> m<sup>2</sup> s<sup>ā1</sup> at the octahedral
and tetrahedral sites, respectively
Ultrahigh-Field <sup>25</sup>Mg NMR and DFT Study of Magnesium Borate Minerals
A series
of well-characterized magnesium borate minerals and synthetic
analogues have been studied via ultrahigh-field <sup>25</sup>Mg solid-state
NMR spectroscopy. Correlations between <sup>25</sup>Mg NMR parameters
and the local structure at the magnesium site(s) are highlighted and
discussed. First-principles density functional theory calculations
of <sup>25</sup>Mg NMR parameters carried out with the WIEN2k software
package support our experimental <sup>25</sup>Mg NMR data. Experimental <sup>25</sup>Mg <i>C</i><sub>Q</sub> values range from 0.7 Ā±
0.1 MHz in hungchaoite to 18.0 Ā± 0.5 MHz in boracite-type Mg<sub>3</sub>B<sub>7</sub>O<sub>13</sub>Br. To our knowledge, the latter <i>C</i><sub>Q</sub> value is the largest reported <sup>25</sup>Mg nuclear quadrupole coupling constant. In general, <i>C</i><sub>Q</sub> values correlate positively with the degree of geometrical
distortion at the Mg site, despite the diversity in nearest-neighbor
ligands (O<sup>2ā</sup>, OH<sup>ā</sup>, H<sub>2</sub>O, F<sup>ā</sup>, Cl<sup>ā</sup>, and Br<sup>ā</sup>) across the series of magnesium borates. Experimental Ī“<sub>iso</sub> values range from 0.2 Ā± 0.5 ppm in hungchaoite to
23 Ā± 3 ppm in grandidierite, which are within the expected chemical
shift range for diamagnetic magnesium borates
Structural Assembly from Phosphate to Germanophosphate by Applying Germanate as a Binder
Structural assembly from phosphate
to germanophosphate by applying germanate as a binder has been achieved.
Two isotypic porous compounds, K<sub>3</sub>[M<sup>II</sup><sub>4</sub>(HPO<sub>4</sub>)<sub>2</sub>]Ā[Ge<sub>2</sub>OĀ(OH)Ā(PO<sub>4</sub>)<sub>4</sub>]Ā·<i>x</i>H<sub>2</sub>O (<i>M</i><sup>II</sup> = Fe, Cd; <i>x</i> = 2 for Fe and 3 for Cd,
denoted as <b>KFeGePO-1</b> and <b>KCdGePO-1</b>, respectively),
contain a known transition-metal phosphate (TMPO) layer, <sub>ā</sub><sup>2</sup>{[<i>M</i><sub>2</sub>(HPO<sub>4</sub>)<sub>3</sub>]<sup>2ā</sup>}, which is built from chains of trans-edge-sharing <i>M</i>O<sub>6</sub> octahedra bridged by <i>M</i>O<sub>5</sub> trigonal bipyramids that were further linked and decorated by phosphate
tetrahedra. The layers are bound by infinite chains of GeO<sub>5</sub>(OH) octahedra, resulting in a 3D open-framework structure with 1D
12-ring channels that are occupied by K<sup>+</sup> ions and water
molecules. The curvature of the TMPO layers and shape of the 12-ring
windows can be tuned by the transition metals because of their JahnāTeller
effect
Structural Assembly from Phosphate to Germanophosphate by Applying Germanate as a Binder
Structural assembly from phosphate
to germanophosphate by applying germanate as a binder has been achieved.
Two isotypic porous compounds, K<sub>3</sub>[M<sup>II</sup><sub>4</sub>(HPO<sub>4</sub>)<sub>2</sub>]Ā[Ge<sub>2</sub>OĀ(OH)Ā(PO<sub>4</sub>)<sub>4</sub>]Ā·<i>x</i>H<sub>2</sub>O (<i>M</i><sup>II</sup> = Fe, Cd; <i>x</i> = 2 for Fe and 3 for Cd,
denoted as <b>KFeGePO-1</b> and <b>KCdGePO-1</b>, respectively),
contain a known transition-metal phosphate (TMPO) layer, <sub>ā</sub><sup>2</sup>{[<i>M</i><sub>2</sub>(HPO<sub>4</sub>)<sub>3</sub>]<sup>2ā</sup>}, which is built from chains of trans-edge-sharing <i>M</i>O<sub>6</sub> octahedra bridged by <i>M</i>O<sub>5</sub> trigonal bipyramids that were further linked and decorated by phosphate
tetrahedra. The layers are bound by infinite chains of GeO<sub>5</sub>(OH) octahedra, resulting in a 3D open-framework structure with 1D
12-ring channels that are occupied by K<sup>+</sup> ions and water
molecules. The curvature of the TMPO layers and shape of the 12-ring
windows can be tuned by the transition metals because of their JahnāTeller
effect