Coexistence of structural and magnetic phases in van der Waals magnet CrI3

CrI3 has raised as an important system to the emergent field of two-dimensional van der Waals magnetic materials. However, it is still unclear why CrI3 which has a ferromagnetic rhombohedral structure in bulk, changed to anti-ferromagnetic monoclinic at thin layers. Here we show that this behaviour is due to the coexistence of both monoclinic and rhombohedral crystal phases followed by three magnetic transitions at TC1 = 61 K, TC2 = 50 K and TC3 = 25 K. Each transition corresponds to a certain fraction of the magnetically ordered volume as well as monoclinic and rhombohedral proportion. The different phases are continuously accessed as a function of the temperature over a broad range of magnitudes. Our findings suggest that the challenge of understanding the magnetic properties of thin layers CrI3 is in general a coexisting structural-phase problem mediated by the volume-wise competition between magnetic phases already present in bulk.

Conversion of Bivalve Shells to Monocalcium and Tricalcium Phosphates: An Approach to Recycle Seafood Wastes

The search for sustainable resources remains a subject of global interest and the conversion of the abundantly available bivalve shell wastes to advanced materials is an intriguing method. By grinding, calcium carbonate (CaCO3) powder was obtained from each shell of bivalves (cockle, mussel, and oyster) as revealed by FTIR and XRD results. Each individual shell powder was reacted with H3PO4 and H2O to prepare Ca(H2PO4)2·H2O giving an anorthic crystal structure. The calcination of the mixture of each shell powder and its produced Ca(H2PO4)2·H2O, at 900 °C for 3 h, resulted in rhombohedral crystal β-Ca3(PO4)2 powder. The FTIR and XRD data of the CaCO3, Ca(H2PO4)2·H2O, and Ca3(PO4)2 prepared from each shell powder are quite similar, showing no impurities. The thermal behaviors of CaCO3 and Ca(H2PO4)2·H2O produced from each shell were slightly different. However, particle sizes and morphologies of the same products obtained from different shells were slightly different—but those are significantly different for the kind of the obtained products. Overall, the products (CaCO3, Ca(H2PO4)2·H2O, and Ca3(PO4)2) were obtained from the bivalve shell wastes by a rapidly simple, environmentally benign, and low-cost approach, which shows huge potential in many industries providing both economic and ecological benefits.

PHYSICOCHEMICAL STUDY AND QUANTITATIVE ANALYSIS SWARNA MAKSHIKA BHASMA.

Swarnamakshika is grouped under Updhatu of Swarna and is composed of Copper, Iron and Sulphur. In this study Swarnamakshika was subjected to Shodhana by Bharjana with Nimbuka swarasa and Shudha Swarnamakshika was given Bhavana with Nimbuka swarasa and subjected to Varahaputa. With ten Varahaputa Bhasma Siddhi Lakshanas were attained swarnamakshika Marana was done by using Nimbuka swarasa until bhasma siddi lakshanas found and it took 10 puta till it attained reddish brown color. The X-ray diffraction analysis showed that d-identified peaks after 10th puta Swarnamakshika bhasma composition is of Iron oxide with rhombohedral crystal system as main component. EDX analysis of Swarna makshika bhasma shows that it contains Iron and Oxygen, as major element and Copper, Sulphur, Carbon, Aluminium, Calcium etc. as minor elements. FESEM study revealed that the particle size of Ashudha and Shudha Swarnamakshika was in the range of 500 nm-3nm. Keywords: Swarnamakshika Bhasma, Nimbuka swarasa, puta

Dielectric Properties of Cr3+ Doped Al2O3 of a Hierarchical Nanostructure Synthesized Using a Highly Porous Precursor of Tubular AlO(OH)⋅αH2O Fibers

Herein, we have developed a Cr3+ doped Al2O3 of a hierarchical nanostructure by a simple two-step synthesis. A pure AlO(OH)⋅αH2O, as synthesized in forms of small tubular fibers by hydrolysis of Al-metal sheets, is easily doped with selective Cr3+ dosages up to 2.0 mol% using an aqueous CrO3. As-synthesized samples exhibit XRD of a single phase Cr3+: Al2O3 of a rhombohedral crystal structure. Average pore-volume is decreased as 98.1, 89.8, and 61.5 cm3-g-1 in the 0.5, 1.0 and 2.0 % Cr% doped samples, with average pore radius of 1.70, 2.17 and 1.90 nm, respectively, as measure from BET specific surface area. Local Al-O vibrations exhibit IR bands of 400 to 1200 cm-1 intrinsic of oxygen polygons. At room temperature, a duly tailored dielectric permittivity of 480 is obtained in a 2.0 mol% Cr3+:Al2O3 and that is enhanced progressively on heating it over 25 to 300 °C, showing a value 6700 at 300 °C in phonon induced dynamics of charge carriers, useful for solid-state electronics.

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

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.

2D Bi2Se3 van der Waals Epitaxy on Mica for Optoelectronics Applications

Bi2Se3 possesses a two-dimensional layered rhombohedral crystal structure, where the quintuple layers (QLs) are covalently bonded within the layers but weakly held together by van der Waals forces between the adjacent QLs. It is also pointed out that Bi2Se3 is a topological insulator, making it a promising candidate for a wide range of electronic and optoelectronic applications. In this study, we investigate the growth of high-quality Bi2Se3 thin films on mica by the molecular beam epitaxy technique. The films exhibited a layered structure and highly c-axis-preferred growth orientation with an XRD rocking curve full-width at half-maximum (FWHM) of 0.088°, clearly demonstrating excellent crystallinity for the Bi2Se3 deposited on the mica substrate. The growth mechanism was studied by using an interface model associated with the coincidence site lattice unit (CSLU) developed for van der Waals epitaxies. This high (001) texture favors electron transport in the material. Hall measurements revealed a mobility of 726 cm2/(Vs) at room temperature and up to 1469 cm2/(Vs) at 12 K. The results illustrate excellent electron mobility arising from the superior crystallinity of the films with significant implications for applications in conducting electrodes in optoelectronic devices on flexible substrates.

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

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+ .

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

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.

Dielectric and Raman spectroscopy studies of (Na0.5Bi0.5)TiO3 lead-free ceramic

In this study, samples of sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) have been prepared using the solid-state technique. Sintering was done at 1200 ºC for 4 h in air atmosphere. X-ray diffraction analysis carried out at room temperature showed the formation of a single-phase compound with a rhombohedral crystal system. Dielectric and Raman spectroscopic characterizations have been performed as a function of temperature. The dielectric study showed the existence of a diffuse phase transition around 330 ºC. The Raman spectra was fitted to the individual Raman peaks. The obtained peaks were analyzed by observing the changes in their respective peak positions and intensities with increasing of temperature. At high temperatures, the results showed discontinuous changes in the phonon frequencies across the rhombohedral-tetragonal transition.