Rhombohedral crystal structure of compounds containing boron-rich icosahedra

1986 ◽  
Author(s):  
B. Morosin ◽  
A. W. Mullendore ◽  
D. Emin ◽  
G. A. Slack
Keyword(s):  
Crystal Structure ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

scholarly journals Analysis Crystal Structure of La0.7Ba(1-xSrx)0.3MnO3 by Sol-Gel Method

2020 ◽  
Vol 3 (1) ◽  
pp. 35-41
Author(s):  
Juli Hartati ◽  
Sitti Ahmiatri Saptari ◽  
Arif Tjahjono
Keyword(s):  
Crystal Structure ◽  
Sol Gel ◽  
Ammonia Solution ◽  
Hot Plate ◽  
Ionic Radii ◽  
Xrd Pattern ◽  
Gel Method ◽  
Sol Gel Method ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

Abstrak.Penelitian tentang struktur kristal  bahan La0.7(Ba1-xSrx)MnO3  menggunakan metode sol-gel telah berhasil dilakukan. Bahan-bahan dasar yang digunakan dicampur di atas hot plate diaduk sambil ditetesi ammonia solution sehingga mencapai pH 7, selanjutnya didiamkan sampai diperoleh bentuk gel. Gel dikeringkan pada suhu 120°C, selanjutnya dilakukan pra-kalsinasi dengan suhu 650°C selama 6 jam, dilanjutkan dengan kalsinasi  pada suhu 1000°C selama 12 jam, dan kemudian disinter pada temperatur 1200°C selama 12 jam. Hasil refinement data  XRD memberikan informasi bahwa struktur kristal  La0.7(Ba1-xSrx)MnO3 adalah rombohedral dengan space grup R-3c. Penambahan substitusi ion Sr2+ mengakibatkan terjadinya penurunan intensitas dan pergeseran puncak ke arah sudut yang lebih besar. Hal ini disebabkan karena pengaruh jari-jari ion Sr2+ yang lebih kecil dibandingkan dengan jari-jari ion Ba2+ . Abstract.In this research,  La0.7(Ba1-xSrx)0.3MnO3  compound (x = 0; 0.2; 0.3; and 0.5) by sol-gel method has been investigated.  The compound used is mixed on a hot plate until reached a pH 7 when dropped ammonia solution, then let stand until turn into a gel. Dehydrated gel at 120°C, pra-calcination at 650°C for 6 hours, calcination t 1000°C for 12 hours, and sintering at 1200°C for 12 hours. The result of refinement XRD pattern shown that samples are single phase with rhombohedral crystal structure with R-3c space group. The intensity decrease and peak list shift to larger angle when Sr-substitution increased, it’s caused  ionic radii of Sr2+ is smaller than Ba2+ .

scholarly journals XAFS study on nanostructured (La;Sr)CoO and (La;Sr)(Co;Fe)O IT-SOFC cathodes

2014 ◽  
Vol 70 (a1) ◽  
pp. C1528-C1528
Author(s):  
Augusto Mejía Gómez ◽  
Joaquín Sacanell ◽  
Analía Soldati ◽  
Marcia Fantini ◽  
Aldo Craievich ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Pore Size ◽  
Reduction Reaction ◽  
Average Pore ◽  
X Ray ◽  
Rhombohedral Crystal Structure ◽  
Sem Study ◽  
Rhombohedral Crystal ◽  
Synchrotron Light ◽  
Mixed Ionic Electronic Conductors

In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of nanostructured La0.6Sr0.4CoO3(LSCO) and La0.6Sr0.4(Co;Fe)O3(LSCFO) cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 10000C in order to produce materials with the desired perovskite-type crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic order of LSCO and LSCFO nanotubes and nanowires for various compositions by X-ray absorption spectroscopies. For this purpose we performed XANES and EXAFS studies on both Co and Fe K edges. These measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only change slightly their oxidation state upon Fe addition. Surprisingly, XANES results indicated that the content of oxygen vacancies is low, even though it is well-known that these materials are mixed ionic-electronic conductors. EXAFS results were consistent with those expected according to the rhombohedral crystal structure determined in previous X-ray powder diffraction investigations.

scholarly journals Low-temperature precausticizing — a hopeful approach for green liquor desilication

TAPPI Journal ◽  
2017 ◽  
Vol 16 (02) ◽  
pp. 57-61
Author(s):  
Xinxing Xia ◽  
Fang Wang ◽  
Xiaojing Qin ◽  
Tingting Tang ◽  
Tianwen Zhou
Keyword(s):  
Crystal Structure ◽  
Calcium Carbonate ◽  
Low Temperature ◽  
Specific Surface ◽  
Amorphous Material ◽  
Stoichiometric Ratio ◽  
Green Liquor ◽  
Silica Removal ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

We investigated silica removal by low-temperature precausticizing and the properties of second causticizing calcium carbonate (CCC). The results showed that about 89.3% of silica removal was achieved when 20% (the stoichiometric ratio) of causticizing quicklime was added for precausticizing at 20ºC for 60 min. After that, silica removal became slow. When no precausticizing quicklime was used to remove silica, the CCC particles had a rhombohedral crystal structure covered with amorphous material. As precausticizing quicklime was increased to 30%, the amorphous material and the crack disappeared, and the specific surface area decreased significantly. When CCC was used as filler, the Cobb value decreased significantly, and the sizing effect improved as precausticizing quicklime increased.

Exploring the magneto-volume anomalies in Dy2Fe17 with unconventional rhombohedral crystal structure

2013 ◽  
Vol 61 (20) ◽  
pp. 7931-7937 ◽  
Author(s):  
Pablo Álvarez-Alonso ◽  
Pedro Gorria ◽  
José L. Sánchez Llamazares ◽  
Gabriel J. Cuello ◽  
Inés Puente Orench ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

Crystal structure of intermetallic phase in Fe–20Cr–4Al–0.5Y alloy by convergent beam electron diffraction

1987 ◽  
Vol 2 (1) ◽  
pp. 16-27 ◽  
Author(s):  
Raghavan Ayer ◽  
J. C. Scanlon ◽  
T. A. Ramanarayanan ◽  
R. R. Mueller ◽  
R. Petkovic-Luton ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Hexagonal Phase ◽  
Intermetallic Phase ◽  
Chemical Compositions ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal ◽  
Convergent Beam ◽  
Relationship Of ◽  
The Relationship

The crystal structure and chemical composition of the intermetallic phase in a Fe-20%Cr-4%Al-0.5%Y (wt. %) alloy were investigated by electron microscopy. Convergent beam diffraction studies revealed that the intermetallic phase forms in three different crystal structures that could coexist in a single grain of the phase. The dominant crystal structure was shown to be hexagonal (a = 0.85, c = 0.84 nm) with a space group most likely to be P63/mmc. Within the hexagonal phase, regions of a rhombohedral crystal structure (a = 0.85, c = 1.26 nm) were observed that had grown in without an apparent phase boundary separating the two crystal structures. The third crystal structure was determined to be monoclinic (a = 0.97, b = 0.85, c = 1.07 nm, and beta = 97.3°) and formed by twinning on the {10$\overline 1$1} planes of the hexagonal phase. The chemical compositions of regions with different crystal structures were comparable and the stoichiometry of the intermetallic phase corresponds to (Fe,Cr)17 (Al,Y)2. The relationship of the observed crystal structures to those previously reported is discussed.

scholarly journals Microwave Absorbing Properties of Polycrystalline La0.67Sr0.33MnO3

2019 ◽  
Vol 5 (1) ◽  
pp. 22
Author(s):  
Wahyu Dian Laksanawati ◽  
Feli Cianda Adrin Burhendi ◽  
Acep Kusdiwelirawan
Keyword(s):  
Crystal Structure ◽  
Functional Groups ◽  
Reflection Loss ◽  
Single Phase ◽  
Sol Gel ◽  
Gel Method ◽  
Sol Gel Method ◽  
Microwave Absorbing Properties ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

Sample \ce {La_{0.67}Sr_{0.33}MnO3} has been successfully synthesized by sol gel method shown by the results of XRD formed a single phase with rhombohedral crystal structure. The results of SEM showed particles are agglomerated yet functional groups \ce {Mn-O-Mn} has been formed based on the results of FTIR. The ability of the sample to absorb the microwaves still lower that the value of reflection loss obtained at $-26.05$ dB.

Microwave-Assisted Solution Combustion Synthesis and Characterization of Thermoelectric Ca3Co2O6 Powders

2013 ◽  
Vol 802 ◽  
pp. 84-88
Author(s):  
Sagulthai Kahatta ◽  
Nopsiri Chaiyo ◽  
Chesta Ruttanapun ◽  
Wicharn Techitdheera ◽  
Wisanu Pecharapa ◽  
...  
Keyword(s):  
Combustion Synthesis ◽  
Solution Combustion Synthesis ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
Solution Combustion ◽  
X Ray ◽  
Microwave Assisted ◽  
Product Characterization ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

The microwave-assisted solution combustion synthesis was applied to the initial synthesizing of Ca3Co2O6powder using glycine as a fuel and nitrate as an oxidant. The as-synthesized powders were calcined at 700-1,000ºC for 4h. Product characterization was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning electron microscope (SEM). The fuel-to-oxidizer molar ratio was found to affect the combustion reaction and character of the powder obtained. The phase composition of powder after calcination at various temperatures has shown that the formation of Ca3Co2O6occurs directly. The calcined powder possesses a rhombohedral crystal structure with an X-ray diffraction pattern that could be matched with the Ca3Co2O6JCPDS: 89-0629. This method is a simple way of synthesizing fine Ca3Co2O6powder with a low calcination temperature.

Preparation and Characterization of Dysprosium (Dy) Ultrafine Nanocrystalline Structures

2008 ◽  
Vol 8 (2) ◽  
pp. 961-966
Author(s):  
Nianduan Lu ◽  
Xiaoyan Song ◽  
Jiuxing Zhang ◽  
Xiangquan Yan ◽  
Markus Rettenmayr
Keyword(s):  
Elastic Modulus ◽  
Nanocrystalline Structure ◽  
Physical And Mechanical Properties ◽  
Gas Condensation ◽  
Rhombohedral Crystal Structure ◽  
Nanocrystalline Structures ◽  
Metallic Nanomaterials ◽  
Efficient Route ◽  
Rhombohedral Crystal

By combining the inert-gas condensation with the SPS technology in an entirely closed system with the oxygen concentration below 0.5 ppm, the pure Dy bulk with the ultrafine nanocrystalline structure has been prepared. Thus a novel and efficient route of preparing nano rare-earth metals, as well as metallic nanomaterials that are highly reactive in the air, is proposed. The thermal, physical and mechanical properties of the prepared ultrafine nanocrystalline Dy bulk have been characterized and compared with those of the conventional raw polycrystalline bulk. It is found that in the nanocrystalline Dy bulk, the starting temperature of phase transformation from hexagonal to rhombohedral crystal structure is reduced by 70 °C in comparison with that of the raw polycrystalline bulk. The electrical resistivity of the ultrafine nanocrystalline bulk is slightly increased by a few percent as compared with that of the polycrystalline bulk, while the thermal conductivity is reduced by 28–35%. The microhardness and the elastic modulus of the ultrafine nanocrystalline Dy bulk are found to be remarkably improved as compared with those of the raw polycrystalline bulk, e.g., the microhardness and the elastic modulus are approximately 2.4 and 2.0 times as high as those of the raw polycrystalline bulk, respectively.

Structural, Optical, Ferroelectric and Magnetic Properties of NiTiO3 Ceramic Synthesized by Citrate Gel Method

2020 ◽  
pp. 2150004
Author(s):  
Pham Van Thang ◽  
Dang Duc Dung ◽  
Luong Huu Bac ◽  
Pham Phi Hung ◽  
Tran Vu Diem Ngoc
Keyword(s):  
Magnetic Properties ◽  
Crystallite Size ◽  
Visible Spectrum ◽  
Xrd Analysis ◽  
X Ray Diffraction ◽  
Gel Method ◽  
Rhombohedral Crystal Structure ◽  
Hall Plot ◽  
Rhombohedral Crystal ◽  
Uv Visible

The NiTiO3 ceramic was synthesized in nanostructured form by citrate gel method. The phase structure, microstructure and magnetic properties of synthesized compounds were investigated by X-ray diffraction (XRD), scanning electron microscope and vibrating sample magnetometer. Williamson–Hall plot was used to calculate the crystallite size and microstrain of sample. The XRD analysis showed the formation of rhombohedral crystal structure of synthesized powders. The crystallite size is about 35[Formula: see text]nm and microstrain is [Formula: see text]. The optical band gap was estimated from UV-Visible spectrum with value of 2.43[Formula: see text]eV. The NiTiO3 samples showed coexistence of ferroelectric and antiferromagnetic properties at room temperature.

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