Normal lattice vibrations and the crystal structure of anisotropic modifications of boron nitride

AbstractBoron nitride (BN) aerogels, composed of nanoscale BN building units together with plenty of air in between these nanoscale building units, are ultralight ceramic materials with excellent thermal/electrical insulation, great chemical stability and high-temperature oxidation resistance, which offer considerable advantages for various applications under extreme conditions. However, previous BN aerogels cannot resist high temperature above 900 °C in air atmosphere, and high-temperature oxidation resistance enhancement for BN aerogels is still a great challenge. Herein, a calcium-doped BN (Ca-BN) aerogel with enhanced high-temperature stability (up to ~ 1300 °C in air) was synthesized by introducing Ca atoms into crystal structure of BN building blocks via high-temperature reaction between calcium phosphate and melamine diborate architecture. Such Ca-BN aerogels could resist the burning of butane flame (~ 1300 °C) and keep their megashape and microstructure very well. Furthermore, Ca-BN aerogel serves as thermal insulation layer, together with Al foil serving as both low-infrared-emission layer and high-infrared-reflection layer, forming a combination structure that can effectively hide high-temperature target (heated by butane flame). Such successful chemical doping of metal element into crystal structure of BN may be helpful in the future design and fabrication of advanced BN aerogel materials, and further extending their possible applications to extremely high-temperature environments.

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Investigating permeability of porous graphene

Thermal Science ◽

10.2298/tsci19s2525m ◽

2019 ◽

Vol 23 (Suppl. 2) ◽

pp. 525-530

Author(s):

Alexander Malozemov

Keyword(s):

Crystal Structure ◽

Natural Gas ◽

Boron Nitride ◽

Graphene Sheet ◽

Surface Form ◽

Helium Mixtures ◽

Porous Graphene ◽

Thermal Oscillations

A graphene sheet with regular pores similar to the surface form of boron nitride is simulated be means of crystallographic constructions. The sheet is represented by the aggregate of carbon atoms in the corresponding positions of the crystal structure which do not experience thermal oscillations. Within the framework of the presented approximation, permeability of porous graphene with respect to natural gas components is theoretically analysed. Based on the results obtained, selectivity of separation for methane-helium mixtures is determined.

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Crystal structure, lattice vibrations, and superconductivity of LaO1−xFxBiS2

Physical Review B ◽

10.1103/physrevb.87.205134 ◽

2013 ◽

Vol 87 (20) ◽

Cited By ~ 61

Author(s):

J. Lee ◽

M. B. Stone ◽

A. Huq ◽

T. Yildirim ◽

G. Ehlers ◽

...

Keyword(s):

Crystal Structure ◽

Lattice Vibrations

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Influence of Molecular and Lattice Vibrations on the Stability of Layered Crystal Structure of Guanidinium Nitrate

physica status solidi (b) ◽

10.1002/1521-3951(199706)201:2<343::aid-pssb343>3.0.co;2-2 ◽

1997 ◽

Vol 201 (2) ◽

pp. 343-354 ◽

Cited By ~ 6

Author(s):

M. Szafra?ski

Keyword(s):

Crystal Structure ◽

Layered Crystal ◽

Lattice Vibrations ◽

Layered Crystal Structure ◽

Guanidinium Nitrate ◽

The Stability

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35Cl NQR Relaxation in Chloral Cyclohexylhemiacetal

Zeitschrift für Naturforschung A ◽

10.1515/zna-1992-1-251 ◽

1992 ◽

Vol 47 (1-2) ◽

pp. 299-304 ◽

Cited By ~ 1

Author(s):

Haruo Niki ◽

Ryokan Igei ◽

Hiroshi Kyan ◽

Takeshi Hamagawa ◽

Takahiro Isono ◽

...

Keyword(s):

Crystal Structure ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Monoclinic Space Group ◽

Lattice Vibrations ◽

Hydrogen Atoms ◽

Oh Groups ◽

Dynamic Disorder ◽

Spin Lattice ◽

35Cl Nqr

AbstractThe crystal structure of cyclohexylhemiacetal (cycHx-CH) was determined at 296 K : monoclinic, space group P21/c, a =1028.7 (9), b = 609.5 (1), c = 1811.9 (4) pm, and ß = 99.79 (3)°, Z = 4, R = 0.0552. The three 35Cl NQR lines in cycHx-CH, T1, T2, and T2*, were measured by a pulsed method at 80-300 K. Below 200 K T1-1 obeyed the T law well, indicating that the spin lattice relaxation is governed by lattice vibrations. The reorientation of CCl3 seems to be responsible for the sharp T: drop observed above 250 K. Shoulders in the T1 vs. 1/T curves indicate the presence of T1 minima at about 240 K. A fluctuation of the EFG due to a dynamic disorder of hydrogen atoms in the OH groups is assumed to explain the T1 minima.

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Investigation of Hexagonal Boron Nitride for Application as Counter Electrode in Dye-Sensitized Solar Cells

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.512-515.242 ◽

2012 ◽

Vol 512-515 ◽

pp. 242-245 ◽

Cited By ~ 4

Author(s):

Shun Jian Xu ◽

Yu Feng Luo ◽

Wei Zhong ◽

Zong Hu Xiao ◽

Xiao Yun Liu

Keyword(s):

Crystal Structure ◽

Solar Cells ◽

Boron Nitride ◽

Counter Electrode ◽

Hexagonal Boron Nitride ◽

Dye Sensitized Solar Cells ◽

Transfer Resistance ◽

Dye Sensitized ◽

Catalytic Material ◽

Sensitized Solar Cells

Hexagonal boron nitride (HBN), which has the same crystal structure as graphite, has been used as catalytic material for a counter electrode in dye-sensitized solar cells (DSCs) to investigate its potential application. X-ray diffraction (XRD) has been used to confirm the crystal structure of HBN, scanning electron microscopy (SEM) has been used to characterize the morphology of HBN film on counter electrode, and electrochemical workstation has been employed to obtain the electrochemical impedance spectroscopy (EIS) and corresponding impedance parameters. Results show that the HBN film has rough surface and porous structure with pore size of less than 1 μm. When employed the HBN counter electrode to DSCs, the conversion efficiency (η) is only about a tenth of that of graphite based DSCs. Low efficiency of HBN based DSCs is induced by high charge transfer resistance (Rct) of HBN counter electrode, which means that HBN can hardly provide catalytic activity for the reduction of the triiodide ion. Therefore, the crystal structure is not a crucial factor to select the catalytic material for a counter electrode in DSCs. Moreover, the short circuit photocurrent density (Jsc) and the open circuit voltage (Voc) of device also evidently depend on the characteristics of catalytic material.

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