Determinants of crystal structure transformation of ionic nanocrystals in cation exchange reactions

Changes in the crystal system of an ionic nanocrystal during a cation exchange reaction are unusual yet remain to be systematically investigated. In this study, chemical synthesis and computational modeling demonstrated that the height of hexagonal-prism roxbyite (Cu1.8S) nanocrystals with a distorted hexagonal close-packed sulfide anion (S2−) sublattice determines the final crystal phase of the cation-exchanged products with Co2+ [wurtzite cobalt sulfide (CoS) with hexagonal close-packed S2– and/or cobalt pentlandite (Co9S8) with cubic close-packed S2–]. Thermodynamic instability of exposed planes drives reconstruction of anion frameworks under mild reaction conditions. Other incoming cations (Mn2+, Zn2+, and Ni2+) modulate crystal structure transformation during cation exchange reactions by various means, such as volume, thermodynamic stability, and coordination environment.

Preparation, Sintering Behavior and Consolidation Mechanism of Vanadium-Titanium Magnetite Pellets

High-quality oxidized pellets are the basis to achieve high-efficiency utilization of vanadium–titanium magnetite (VTM) ores. Bentonite was used as a binder of VTM. The main phase composition of VTM is titanomagnetite and ilmenite. When the amount of bentonite is 1%, the compressive strength and dropping strength of VTM pellets can meet the requirements. To improve metallurgical properties, the pellets need to be roasted. The best conditions for roasting are as follows: calcination temperature of 1523 K and a calcination time of 20 min. The consolidation mechanism, phase transformation, and crystal structure transformation of VTM in the process of oxidation roasting are also explained.

Mechanisms of sodiation in anatase TiO2 in terms of equilibrium thermodynamics and kinetics

Anatase TiO2 is a promising anode material for sodium-ion batteries (SIBs). However, its sodium storage mechanisms in terms of crystal structure transformation during sodiation/de-sodiation processes are far from clear. Here,...

Structural transition and magnetic properties of high Cr-doped BiFeO3 ceramic

Magnetic properties of BiFe1-xCrxO3 perovskite-type solids reaction synthesized at high pressure were investigated and a magnetic phase diagram was established. X-ray diffraction data revealed a crystal structure transformation from rhombohedral to monoclinic as Cr3+ ions substituted Fe ions in the samples. Néel temperature TN and spin-reorientation temperature TSR were determined from dM/dT by measuring the temperature dependence of magnetization (M-T). The magnetization results indicated that TN and TSR were strongly dependent on Cr3+ ion doping; both TN and TSR decreased with the increase of Cr3+ doping. The magnetic hysteresis loops investigated at room temperature reflected an antiferromagnetic behavior from x= 0.4 to 0.6 and weak ferromagnetic at x=1.0. Besides, the remnant magnetization Mr and maximum magnetization Mmax increased with increasing x from 0.4 up to 1.0. The Cr doping was found to be helpful in reducing coercivity Hc for the magnetic samples from x= 0.4 to 0.8 and their applications as magnetic sensors are possible.

Crystal structure, thermodynamics, and crystallization of bio-based polyamide 56 salt

Polyamide 56 is regarded as one of the most promising materials for the textile industry. This report gives the crystallization route of high-quality polyamide 56 monomers, and its crystal structure, transformation behaviors, and solubility.

Long-range propagation of protons in single-crystal VO2 involving structural transformation to HVO2

Vanadium dioxide (VO2) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature. Ion-doping to VO2 dramatically alters its transport properties and the MIT temperature. Recently, insulating hydrogenated VO2 (HVO2) accompanied by a crystal structure transformation from VO2 was experimentally observed. Despite the important steps taken towards realizing novel applications, essential physics such as the diffusion constant of intercalated protons and the crystal transformation energy between VO2 and HVO2 are still lacking. In this work, we investigated the physical parameters of proton diffusion constants accompanied by VO2 to HVO2 crystal transformation with temperature variation and their transformation energies. It was found that protons could propagate several micrometers with a crystal transformation between VO2 and HVO2. The proton diffusion speed from HVO2 to VO2 was approximately two orders higher than that from VO2 to HVO2. The long-range propagation of protons leads to the possibility of realizing novel iontronic applications and energy devices.