Rositsa Titorenkova

Effects of high energy dry milling on biphase calcium phosphates

Abstract Abstract The effect of high energy dry milling on the structural and crystalline state of sintered biphase calcium phosphates was studied. After various periods of grinding, the initial biphase calcium phosphate material alters its crystalline structure and phase composition. The phase transformations achieved during milling were recorded by powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy and chemical analysis. X-ray diffraction analysis of samples milled for 20 h showed that the initial composition of the biphase ceramics changed and part of β-tertiary calcium phosphate was nanocrystalline and partially in amorphous state. Hydroxylapatite fully transformed into nanocrystalline phase. Cytotoxicity tests of samples milled for 20 h clearly present cellular viability with pronounced biological activity.

Mg- and Zn-modified calcium phosphates prepared by biomimetic precipitation and subsequent treatment at high temperature

Powders of magnesium-modified as well as zinc-modified calcium phosphates (Me-β-TCP and HA) with a (Ca2++Mg2++Zn2++Na++K+)/P ratio of 1.3–1.4 and various Me2+/(Me2++Ca2+) ratios (from 0.005 to 0.16) were prepared in biomimetic electrolyte systems at pH 8, mother liquid maturation and further syntering at 600–1000°C. Some differences in zinc and magnesium modifications have been prognosed on the basis of thermodynamic modeling of the studied systems and explained by the Mg2+ and Zn2+ ion chemical behaviour. The temperature as well as the degree of Zn2+ and Mg2+ ions substitutions were found to stabilize the β-TCP structure and this effect was more prononced for zinc. Thus, zinc-modified β-TCP powders consisting of idiomorphic crystals were obtained through sintering of Zn2+ ion substituted calcium phosphates precursors at 800–1000°C. The Mg2+ ion substitution leads to obtaining magnesium-modified β-TCP with spherical grains.

Effect of Doping on the Structure and Raman Spectra of Bi4Ge3O12

Single crystals of Bi4Ge3O12 (BGO) doped with Mn (concentration of 0.8×1018 cm−3), V (6.8×1018 cm−3), Co (0.1×1017 cm−3), and V+Co(4.8×1018+4.6×1017 cm−3) have been grown by the Czochralski method and studied by single‐crystal X‐ray diffraction and polarized Raman spectroscopy. Upon doping with V, Co and Mn the unit‐cell parameter decreases by approximately 0.01 A, the BiO6 octahedra become more irregular, while the volume and the local distortion of GeO4 tetrahedra decrease. The degree of structural changes depends on the type of dopant. Taking into account the variations in the dopant concentration, one can conclude that Co is most effective, while V is least effective doping element. The Raman scattering experiments show that doping affects the intensity ratio between the longitudinal and transverse component of the polar phonon modes. The doping‐induced changes in the intensity ratio indicate strengthening of the existing local electric fields. This is consistent with the enlarged deformation of BiO6 ...

Enhanced Raman Scattering from LO Phonons in Doped Semiconductors

Raman scattering spectra of pure and doped Bi4Ge3O12 crystals are investigated in the region 100–350 cm−1 where several polar modes are symmetry‐allowed in crossed polarizations. It is shown that doping with Co, V and Co+V with concentrations ∼1016–1018 cm−3 leads to a considerable increase of the scattering intensities for LO phonons. The contribution of impurity‐induced scattering is analyzed and the possible mechanisms leading to the observed effect are discussed.