5 research outputs found
Synthesis and Crystal Structures of Ca<sub>4</sub>SiN<sub>4</sub> and New Polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>
Single crystals of
Ca<sub>4</sub>SiN<sub>4</sub> were found in the product prepared by
heating Ba, Ca, Si, NaN<sub>3</sub>, and Na at 900 °C. Ca<sub>4</sub>SiN<sub>4</sub> [space group <i>P</i>2<sub>1</sub>/<i>c</i> (No. 14), <i>Z</i> = 4, <i>a</i> = 9.1905(4) Å, <i>b</i> = 5.9775(3) Å, <i>c</i> = 11.0138(7) Å, β = 116.4054(17)°] is
isotypic with Ca<sub>4</sub>GeN<sub>4</sub> and K<sub>4</sub>SiO<sub>4</sub>. Isolated [SiN<sub>4</sub>]<sup>8–</sup> tetrahedra
were identified in the structure by single-crystal X-ray diffraction.
After reheating the product at 900 °C, a new polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub> crystallized. The space group
of the polymorph [<i>C</i>2/<i>m</i> (No. 12), <i>Z</i> = 4, <i>a</i> = 6.2712(5) Å, <i>b</i> = 10.0175(8) Å, <i>c</i> = 12.0287(8) Å, β
= 99.303(2)°] is different from <i>C</i>2/<i>c</i> previously reported for Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>, while both polymorphs are composed of Ca<sup>2+</sup> and edge-sharing
double tetrahedra [Si<sub>2</sub>N<sub>6</sub>]<sup>10–</sup>
Synthesis and Crystal Structures of Ca<sub>4</sub>SiN<sub>4</sub> and New Polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>
Single crystals of
Ca<sub>4</sub>SiN<sub>4</sub> were found in the product prepared by
heating Ba, Ca, Si, NaN<sub>3</sub>, and Na at 900 °C. Ca<sub>4</sub>SiN<sub>4</sub> [space group <i>P</i>2<sub>1</sub>/<i>c</i> (No. 14), <i>Z</i> = 4, <i>a</i> = 9.1905(4) Å, <i>b</i> = 5.9775(3) Å, <i>c</i> = 11.0138(7) Å, β = 116.4054(17)°] is
isotypic with Ca<sub>4</sub>GeN<sub>4</sub> and K<sub>4</sub>SiO<sub>4</sub>. Isolated [SiN<sub>4</sub>]<sup>8–</sup> tetrahedra
were identified in the structure by single-crystal X-ray diffraction.
After reheating the product at 900 °C, a new polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub> crystallized. The space group
of the polymorph [<i>C</i>2/<i>m</i> (No. 12), <i>Z</i> = 4, <i>a</i> = 6.2712(5) Å, <i>b</i> = 10.0175(8) Å, <i>c</i> = 12.0287(8) Å, β
= 99.303(2)°] is different from <i>C</i>2/<i>c</i> previously reported for Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>, while both polymorphs are composed of Ca<sup>2+</sup> and edge-sharing
double tetrahedra [Si<sub>2</sub>N<sub>6</sub>]<sup>10–</sup>
Synthesis and Crystal Structures of Ca<sub>4</sub>SiN<sub>4</sub> and New Polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>
Single crystals of
Ca<sub>4</sub>SiN<sub>4</sub> were found in the product prepared by
heating Ba, Ca, Si, NaN<sub>3</sub>, and Na at 900 °C. Ca<sub>4</sub>SiN<sub>4</sub> [space group <i>P</i>2<sub>1</sub>/<i>c</i> (No. 14), <i>Z</i> = 4, <i>a</i> = 9.1905(4) Å, <i>b</i> = 5.9775(3) Å, <i>c</i> = 11.0138(7) Å, β = 116.4054(17)°] is
isotypic with Ca<sub>4</sub>GeN<sub>4</sub> and K<sub>4</sub>SiO<sub>4</sub>. Isolated [SiN<sub>4</sub>]<sup>8–</sup> tetrahedra
were identified in the structure by single-crystal X-ray diffraction.
After reheating the product at 900 °C, a new polymorph of Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub> crystallized. The space group
of the polymorph [<i>C</i>2/<i>m</i> (No. 12), <i>Z</i> = 4, <i>a</i> = 6.2712(5) Å, <i>b</i> = 10.0175(8) Å, <i>c</i> = 12.0287(8) Å, β
= 99.303(2)°] is different from <i>C</i>2/<i>c</i> previously reported for Ca<sub>5</sub>Si<sub>2</sub>N<sub>6</sub>, while both polymorphs are composed of Ca<sup>2+</sup> and edge-sharing
double tetrahedra [Si<sub>2</sub>N<sub>6</sub>]<sup>10–</sup>
Crystal Growth Conditions of Types I and II Na–Si Clathrates by Evaporation of Na from a Na–Si–Sn Solution
Single
crystals of the type I clathrate Na<sub>8</sub>Si<sub>46</sub> were
synthesized by the evaporation of Na from a Na–Si–Sn
solution (Na:Si:Sn = 6:2:1 molar ratio) at 723–873 K under
an Ar atmosphere of 10<sup>5</sup> Pa. In the mixture of type I and
type II clathrates prepared by heating at 773 K for 72 h, type I single
crystals with sizes of up to 5 mm were found. A single phase of single
crystals of the Na<sub>24</sub>Si<sub>136</sub> type-II clathrate
having a {111} crystal facet of about 2 mm on one side was obtained
by heating at 873 K for 9 h
High-Pressure Diffusion Control: Na Extraction from NaAlB<sub>14</sub>
A novel synthesis technique, called the high-pressure
diffusion
control (HPDC) method, was developed in this study. The method combined
the high-pressure synthesis using a cubic anvil apparatus and an anisotropic
diffusion control technique; the electrical processing in high-pressure
and high-temperature environments of up to 4 GPa and over 1000 °C
is enabled by simultaneously adjusting the temperature, pressure,
and voltage. This nonequilibrium state is effective in creating metastable
materials. The developed novel technique was applied to polycrystalline
NaAlB14 with a boron covalent framework. Although electronic
conduction is dominant in this material and no Na-ion conduction is
observed even at high temperatures, the HPDC method successfully extracted
Na ions by utilizing the difference in bond strength between Na and
B, creating the metastable material AlB14 while maintaining
its basic crystal structure. During the decrease in the Na concentration,
applying a high pressure compressed the sample according to the volume
change and maintained good contact at the intergrain boundary in the
polycrystalline sample, promoting Na-ion diffusion. The Na extraction
functioned as electron carrier modulation and significantly reduced
the electrical resistivity. The developed HPDC method is expected
to be applicable to various compounds with a difference in the bond
strength between constituent elements and has the potential to open
up new avenues in the inorganic synthesis of polycrystalline metastable
materials with dense sintered states and modulate their physical properties