Nanocrystalline hydroxyapatite powders by a chitosan–polymer complex solution route: Synthesis and characterization

Nanocrystalline hydroxyapatite (HAp) powders were successfully synthesized by a simple method using chitosan–polymer complex solution. To obtain HAp nanopowders, the prepared precursor was calcined in air at 400–800 °C for 2 h. The phase composition of the calcined samples was studied by X-ray diffraction (XRD) technique. The XRD results confirmed the formation of HAp phase with a small trace of monotite phase. With increasing calcination temperature, the crystallinity of the HAp increased, showing the hexagonal structure of HAp with the lattice parameter a in a range of 0.94030–0.94308 nm and c of 0.68817–0.68948 nm. The particle sizes of the powder were found to be 55.02–73.36 nm as evaluated by the XRD line broadening method. The chemical composition of the calcined powders was characterized by FTIR spectroscopy. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the calcined powders. TEM investigation revealed that the prepared HAP samples consisted of rod-like nanoparticles having the particle size in the range of 100–300 nm. The corresponding selected-area electron diffraction (SAED) analysis further confirmed the formation of hexagonal structure of HAp.     

Nanofibers of barium strontium titanate (BST) by sol-gel processing and electrospinning

This paper describes the fabrication of barium strontium titanate (Ba0.6Sr0.4TiO3 or BST) nanofibers by electrospinning method using a solution that contained poly(vinylpyrrolidone) and a sol-gel solution of BST. The as-spun and calcined BST/PVP composite nanofibers were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun BST/PVP composite nanofibers at above 700 degrees C in air for 2 h, BST nanofibers of 188+/-25 nm in diameter having well-developed cubic-perovskite structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature. Calcination at below 700 degrees C resulted in amorphous phase whereas BST with second phase such as barium titanate were formed at above 700 degrees C. Diameters of the nanofibers decreased from 208+/-35 to 161+/-18 nm with increasing calcination temperature between 600 and 800 degrees C.     

Structure and magnetic properties of Zn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol)

Room-temperature ferromagnetism was observed in Zn_0.9Co_0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn_0.9Co_0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor binding energy of ZnO.     

Magnetic behavior of nanocrystalline powders of Co-doped ZnO diluted magnetic semiconductors synthesized by polymerizable precursor method

This paper reports the first synthesis of nanocrystalline powders of Co-doped ZnO (i.e. Zn_0.9Co_0.1O) diluted magnetic semiconductor by a polymerizable precursor method using nitrate salts of Zn and Co and a mixed solution of citric acid and ethylene glycol as a chelating agent and reaction medium, respectively. The polymeric precursors were characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at 723 K. The precursors were calcined at different temperatures of 773, 873, 973, and 1073 K for 1 h to obtain nanocrystalline powders. The morphology and crystalline size of the calcined particles were evaluated by SEM, TEM and Scherrer's equation. The average particle sizes calcined at 773, 873, 973, and 1073 K for 1 h were, respectively, 20, 60, 80, 150 nm, obtained from TEM. The XRD and Fourier transmission infrared (FT-IR) results indicated that the synthesized Zn_0.9Co_0.1O powders have the pure wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. Room temperature magnetization results revealed a ferromagnetic behavior for the Zn_0.9Co_0.1O powders. Although the specific magnetization seemed to change with the particle size but there was no clear dependency since the largest magnetization was observed in the powders calcined at 873 K (60 nm). Instead, the specific magnetization appeared to show a trend of dependency on the lattice constant c of the wurtzite unit cell.