Effects of Sr2+/Zn2+ co-substitution on crystal structure and properties of nano-β-tricalcium phosphate

The incorporation of therapeutic ions like Sr²⁺, Si⁴⁺, Zn²⁺ and Li⁺ into biomaterials has become a promising approach to promote bone regeneration. However, the effects of Sr²⁺ and Zn²⁺ co-substitution on the crystal structure and properties of β-tricalcium phosphate (β-TCP) have not been elucidated well. In this study, Sr²⁺/Zn²⁺ co-substituted β-tricalcium phosphate (SrZnTCP) nano-powders with different extents of substitution (0–4.8 mol%) were synthesized by poly(ethylene glycol)-assisted co-precipitation and subsequent heat treatment. The as-synthesized SrZnTCP nano-powders were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, Rietveld refinement and differential scanning calorimetry. The results showed that the conversion of calcium-deficient apatite to β-TCP was achieved after heat-treatment above 800 °C. The a-axis and c-axis lattice parameters gradually decreased with increasing level of Sr²⁺/Zn²⁺ co-substitution in β-TCP lattice. Sr²⁺ and Zn²⁺ preferentially occupied the ninefold coordinated Ca (4) sites and the sixfold coordinated Ca (5) sites, respectively. The co-substitution of Sr²⁺ and Zn²⁺ for Ca²⁺ significantly improved the thermal stability of β-TCP. The release rate of Zn²⁺ from SrZnTCP depended on Ca²⁺ concentration over 63-day immersion in PBS solution while that of Sr²⁺ was not affected by Ca²⁺ concentration. The amount of Sr²⁺ released increased with increasing Sr²⁺ content in SrZnTCP. Collectively, SrZnTCP showed great promise as a Sr²⁺/Zn²⁺-releasing biomaterial for bone repair, although no obvious mineralization was observed on β-TCP and SrZnTCP disc samples during 56 days of immersion in simulated body fluid.     

Compositional tailoring effect on crystal structure,mechanical and thermal properties of γ-AlON transparent ceramics

In view of the practical application of γ-AlON as a promising transparent structural ceramic, in-depth insight into its mechanical and thermal properties is essential. The solid-state MAS NMR technique was combined with XRD Rietveld refinement to confirm the crystal structure of Al_(8+x)/3O_4-xN_x (x = 0.299–0.575). These structural parameters were further applied to predict hardness and elastic properties based on theoretical exploration, which are in good agreement with the experimental values. A slight enhancement of mechanical properties with increasing nitrogen concentration is attributed to the stronger chemical bond in octahedra. The experimental thermal conductivity of γ-AlON transparent ceramics was improved slightly with the rise of x in the temperature range from 298 K to 1074 K. The intrinsic lattice thermal conductivity was determined by eliminating the extrinsic phonon scattering as well as the thermal radiation. The reason for the discrepancy between experimental and intrinsic thermal conductivity was revealed. The present methods provided powerful and accessible guidelines in optimizing the mechanical and thermal properties of oxynitride materials.     

Effect of Sr2+ and Ba2+ doping on structural stability and mechanical properties of La2NiO4+δ

Structural and mechanical Characterizations of La_1.8M_0.2NiO_4+δ (M: Sr and Ba) prepared by low frequency ultra-sound assisted synthesis technique and sintered at different temperatures were studied. HRTEM and XRD analyses showed the uniform shape of calcined nanocrystalline powders with the particle size of less than 100?nm with mixed phases, which were refined by Rietveld method using orthorhombic (Fmmm) and tetragonal (F4/mmm) structures. Sintering La_1.8Sr_0.2NiO_4+δ and La_1.8Ba_0.2NiO_4+δ compacted discs at temperatures higher than 1300?°C and 1250?°C, respectively, resulted in appearance of extra peaks close to a monoclinic phase. Doping La₂NiO_4+δ with Sr²⁺ and Ba²⁺ did not affect its sinterability and average grain size significantly, however, Ba²⁺ improved the elastic modulus and microhardness, while Sr²⁺ improved the fracture toughness.     

Effect of γ-radiation on the structure and thermal properties of polyacrylonitrile fibres

-Radiation significantly affects both the initial structure and the thermal properties of PAN fibres. The following are probably the most important results of radiation exposure: the temperature of the beginning of cyclization decreases; the exothermic nature of cyclization decreases so that the weight losses in the region of the m.p. decrease, indicating destructive processes in the polymer chain; when irradiated samples are heated, intermolecular cross-links form with the participation of oxygen; the duration of oxidation of the fibres before a given density level is attained is reduced significantly.St. Petersburg University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 18–21, May–June, 1995.     

Effect of γ-radiation on the structure and mechanical properties of polycaproamide fibres

Not only the tensile characteristics but also the character of the P(ε) and ε(T)curves change in γ-irradiation of PCA fibres. Irradiation in a forevacuum causes fewer changes in the structure and mechanical properties of PCA fibres than irradiation in air. In irradiation of PCA fibres in air, a shrinkage stage is detected, replaced by a stage of spontaneous lengthening as the absorbed dose increases. In the case of irradiation in a forevacuum (in the dose range studied), only the shrinkage stage is observed. The shrinkage stage is characterized by slight disordering of the structure of the polymer and an increase in the angle of disorientation of crystallites. Recrystallization processes activated by the radiation and to a great degree due to an increase in the molecular mobility because of fragmentation of transfer chains take place in the spontaneous lengthening stage. Translated from Khimicheskie Volokna, No. 2, pp. 47–50, March–April, 1998.     

First-principles calculations of electronic structures and optical,phononic, and thermodynamic properties of monoclinic α-spodumene

To further the applications of spodumene in ceramic materials, we performed first-principles density functional theory calculations using a quasi-harmonic approximation to investigate the electronic structures and optical, phononic, and thermodynamic properties of monoclinic types of α-spodumene with C2 and P2₁ structures. The electronic structures of C2- and P2₁-spodumene including band structure and density of states, were observed to be similar. These spodumene can be treated as wide-direct-band-gap insulators with band-gap widths of 5.537 eV for C2 -spodumene and 6.335 eV for P2₁-spodumene. The optical properties of C2- and P2₁-spodumene indicated that both C2- and P2₁-spodumene were found to be optically anisotropic and they can be used for UV shielding in optical devices. Additionally, we investigated the phononic properties of these spodumene to explore their thermodynamic characteristics, and found that both types are dynamically stable.     

Effects of various rare-earth additives on the sintering and transmittance of γ-AlON

Several rare earth elements (Sc, La, Pr, Sm, Gd, Dy, Er, and Yb) were evaluated to develop a sintering additive for transparent γ-AlON. After adding 0.2 wt. % of each of the rare earth additives to the α-Al₂O₃ and AlN starting material, hot pressing was performed at 1850 °C for 1 h under 20 MPa as a screening test, whereby the γ-AlON with Pr-nitrate showed the highest transmittance of 60.4 % at 632 nm. Two-step pressureless sintering was conducted as a separate test for the same starting material after adjusting the amount of Pr-nitrate to 0, 0.1, or 0.2 wt. % to enhance transmittance. The γ-AlON with 0.1 wt. % Pr-nitrate showed the highest transmittance of 80.36 % after 1st and 2nd sintering steps at 1610 and 1940 °C, respectively, indicating that Pr can be an alternative sintering additive to conventional Y₂O₃, MgO, and La₂O₃ for the fabrication of transparent γ-AlON.     

Structural-microstructural characterization and optical properties of Eu3+,Tb3+-codoped LaPO4·nH2O and LaPO4 nanorods hydrothermally synthesized with microwaves

Rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄·nH₂O single-crystal nanorods with the compositions La_0.99999-xEu_xTb_0.00001PO₄·nH₂O (x?=?0–0.03), La_0.99999-yTb_yEu_0.00001PO₄·n′H₂O (y?=?0–0.010), and La_0.99999-zTb_zEu_0.000007PO₄·n′′H₂O (z?=?0–0.012) were hydrothermally synthesized with microwaves. It is shown that the Eu³⁺,Tb³⁺ codoping does not affect the thermal stability of these nanorods, which is due to the formation of substitutional solid solutions with both Eu³⁺ and Tb³⁺ replacing La³⁺ in the crystal lattice. Moreover, it is also shown that monazite-type Eu³⁺,Tb³⁺-codoped LaPO₄ single-crystal nanorods can be obtained by calcining their rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄·(n,n′ or n′′)H₂O counterparts at moderate temperature in air, and that they are thermally stable. It is also observed that, for the same Eu³⁺,Tb³⁺-codoping content, the monazite-type Eu³⁺,Tb³⁺-codoped LaPO₄ nanorods exhibit higher photoluminescent efficiency than the rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄· (n,n′ or n′′)H₂O nanorods. Moreover, it is found that the highest photoluminescence emission corresponds to the monazite-type La_0.96999Eu_0.02Tb_0.00001PO₄ nanorods for the La_0.99999-xEu_xTb_0.00001PO₄ system. However, for those compositions energy transfer from Tb³⁺ to Eu³⁺ does not occur. In addition, for an efficient energy transfer to occur, a content of at least 1?mol% Tb³⁺ is needed in all the studied materials.     

Effects of the ionizing irradiation of γ-rays,X-rays,and UV-rays on the optical properties of Ag-contained/Ag-free photo-thermo-refractive glass

To simulate the effects of ionizing irradiation on photo-thermo-refractive (PTR) glass in a cosmic environment, the optical properties changes under ionizing irradiation (γ-, X- and UV-ray) were investigated on PTR-glass with and without Ag doped (named as PTR-S and PTR-F, respectively) samples. Thermoluminescence (TL), transmission electron microscopy (TEM) measurements, UV-VIS absorption spectroscopy analysis, Gaussian peak fitting, and continuous wave electron paramagnetic resonance (CW-EPR) were used to determine the species of the irradiation-induced color centers. The radiation resistance properties of the Ag-species on the PTR-S glass were evaluated by comparing the defect center concentrations in the irradiated PTR-S and PTR-F glasses. The results showed that absorption in PTR-F and PTR-S glass increased significantly with increasing γ-irradiation dose, which was related to HC₁, HC₂, E′, L, ETC defect centers and Ag-species, and the formation of HC₁, HC₂, E’, and L-centers was reduced by the doping of Ag into the PTR-S glass matrix. Compared with the γ-irradiation, X-irradiation showed a similar effect. In comparison, UV-irradiation induced fewer defect centers and smaller Ag (NPs). This discrepancy could be caused by variations in photon energies.     

Enhanced narrow green emission and thermal stability in γ-AlON: Mn2+, Mg2+ phosphor via charge compensation

A series of novel green emitting γ-AlON: Mn²⁺, Mg²⁺ and γ-AlON: Mn²⁺, Mg²⁺, M (M?=?Li⁺, Na⁺, K⁺, Si⁴⁺) phosphors were fabricated with the gas-pressure sintering reaction process. The phase structure, morphology and photoluminescence properties of the phosphors were characterized via X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. Meanwhile, the charge compensation methods were utilized to eliminate the disadvantage of charge imbalance between Al³⁺ and Mn²⁺. The results show that the luminescence intensity of Mn²⁺ was maximally enhanced by the introduction of Si⁴⁺ ions, which was 2.36 times that of the sample without charge compensator. Moreover, as the temperature reached at 150?°C, thermal stability of the samples contained charge compensator Li⁺ and Si⁴⁺ were improved to 93% and 90% of that the room temperature, respectively, while the original sample was 85%. These luminescence properties were enhanced due to the introduction of charge compensators which reduce defects caused by charge imbalance. In addition, the specific mechanisms were discussed in detail. In general, the charge compensation could be used as an effective strategy to strengthen thermal stability and luminescence performances of phosphors.     

Influences of La and Er on structure and properties of Bi2O3–B2O3 glass

Bi₂O₃·2B₂O₃ glasses doped with La₂O₃ and Er₂O₃ were prepared by the melting-quenching method with AR-grade oxides. IR analysis was used to investigate the glass network structure. The characteristic temperatures including the glass transition temperature (T_g), crystallization temperature (T_p), and melting temperature (T_m) were estimated by DSC. The coefficient of thermal expansion (α), mass density (D), and Vickers hardness (H_v) were also measured. The results show that the basic network structure of Bi₂O₃·2B₂O₃ glasses doped with rare-earth oxides consists of chains composed of [BO₃], [BO₄], and [BiO₆] units. La₂O₃ and Er₂O₃ act as network modifiers. As the doping concentrations of the rare-earth oxides were increased, T_g increased and α decreased, indicating that a more rigid glass was obtained. Er₂O₃ reduces the melting temperature and prevents glass crystallization. La₂O₃ contributes to the improvement of the microhardness of Bi₂O₃·2B₂O₃ glass.     

掺杂RE3+对CaAl2O4:Eu2+,Nd3+发光性能的影响

以燃烧法合成了CaAl2O4∶Eu2+,Nd3+,RE3+紫色长余辉发光材料。实验结果表明,掺杂辅助激活剂Pr3+和Ce3+对CaAl2O4∶Eu2+,Nd3+磷光体发光性能有明显影响。掺杂Pr3+的CaAl2O4∶Eu2+,Nd3+样品的发射峰蓝移;掺杂Ce3+的CaAl2O4∶Eu2+,Nd3+样品的发射峰红移。Pr3+或Ce3+掺杂,可以提高CaAl2O4∶Eu2+,Nd3+磷光体的初始亮度,Pr3+或Ce3+在其中起到增加陷阱密度,提高发光亮度的作用。     

Impact of the O/P ratio on the optical properties and structures of fluoride–phosphate glass

Ca(PO₃)₂–AlF₃–CaF₂–BaF₂–BaO glasses were prepared by the melt quenching method, and the effects of the O/P ratio on the optical properties and glass structure were investigated. The bandgap energy showed no significant change at O/P = 3.0–3.4 but drastically decreased with the increase in the O/P from 3.6 to 4.0. In addition, the refractive index dispersion was analyzed based on the Lorentz model, and it was found that the decrease in the resonance frequency in the ultraviolet region with the increase in the O/P ratio resulted in an increase in the refractive index and dispersion. Analysis of the infrared absorption and Raman scattering spectra revealed that the phosphate chains were broken, and isolated Q⁰ units were generated with the increase in the O/P ratio from 3.6 to 4.0. Based on the structural change of the glass, the origin of the nonlinear dependence of the optical properties on the O/P ratio was discussed.     

Effect of Sr/Ca substitution on phase structure and photoluminescence properties of micro-SrxCa1−xAlSiN3: Eu2+ phosphor for high CRI white LEDs

Sr_xCa_1−xAlSiN₃: Eu²⁺ phosphors were prepared by using the high temperature solid state reaction in a 1.1 Mpa N₂ atmosphere. The phase structures, photoluminescence (PL) properties, and chromaticity properties of the phosphors affected by Sr/Ca Substitution have been investigated in detail. With increasing Sr content (x value), the crystal grain became bigger and the average grain size increased from 5 µm to 10 µm. PL emission bands of Sr_xCa_1−xAlSiN₃: Eu²⁺ showed a blue-shift from 660 (x=0) to 617 nm (x=0.8), the shoulder of the excitation spectra around 550 nm showed a slightly blue-shift and decay lifetime shortened from 776.96 (x=0.2) to 642.35 ns (x=0.8). Both the emission and excitation intensity of peak position increased with Sr content increased. The ideal white light with high CRI (Ra>88) can be obtained by mixing the Sr_xCa_1−xAlSiN₃: Eu²⁺ phosphors and commercial green phosphors with appropriate proportion of the components.     

Influence of Fe3+-doping on optical properties of CeO2−y nanopowders

Ce_1?xFe_xO_2?y (0≤x≤0.05) nanopowders were synthesized using hydrothermal method at low calcination temperature and low doping regime. Structural and morphological characterization has been carried out by the X-ray diffraction method and non-contact atomic force microscopy. Vibrational properties were investigated by Raman spectroscopy. It was observed that the content of oxygen vacancies increased significantly with Fe doping up to 3 mol%. For higher dopant concentration, phase separation was detected. The optical properties of pure and Fe³⁺-doped CeO_2?y samples were investigated by spectroscopic ellipsometry. Several analytical models were applied to analyze the optical absorption onset of ceria defective structure. It was found that, Cody–Lorentz model most suitably described the sub-band gap region of CeO_2?y nanopowders and consequently gave more accurate band gap values, which are closer to the direct band gap transitions than to the indirect ones. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe-doped samples can significantly improve the optical activity of nanocrystalline ceria.     

燃烧法合成SrAl2O4∶Eu2+,Nd3+纳米长余辉发光材料

采用燃烧法合成了SrAl2O4∶Eu2+,Nd3+纳米长余辉发光材料。应用正交法优化了合成条件,得到最佳制备条件为,炉温在650℃,硼酸摩尔分数为0.10,n(Al)/n(Sr)为2.0,尿素加入4倍理论用量,Nd2O3物质的量为0.00025mol。研究结果表明,SrAl2O4纯相的铝锶比n(Al)/n(Sr)在1.5～2.0之间,铝锶比从1.0到3.5,依次得到Sr3Al2O6、SrAl2O4、Sr4Al14O25和SrAl12O19的纯相或混相样品。硼酸摩尔分数为0.10的样品发育较完全,晶化程度好。与高温固相法的样品相比,发射峰发生不同程度蓝移。样品平均晶粒尺寸小于100nm。     

Structural effects on the cyclability of the alkaline γ-MnO2 electrode

The cyclability of manganese dioxide samples with a wide range of initial properties has been investigated using electrochemical methods. Cycling revealed that a common change occurs in all materials irrespective of initial properties, with the discharge behaviour standardised by the tenth cycle. Modeling of the discharge behaviour revealed the steady decline in the capacity with cycling can primarily be assigned to lower potential pyrolusite domains. Furthermore, an examination of chemically reduced and re-oxidised γ-MnO₂ revealed an irreversible expansion of the γ-MnO₂ lattice upon reduction arising from localised buckling of the oxygen framework.     

Effect of lattice structure evolution and stacking fault energy on the properties of Cu–ZrO2/GNP nanocomposites

A hybrid nanocomposite comprising nanosized ZrO₂ and graphene nanoplatelet (GNP)-reinforced Cu matrix was synthesised via powder metallurgy. The influence of sintering temperature and GNP content on the electrical and mechanical behaviour of the Cu–ZrO₂/GNP nanocomposite was investigated. The ZrO₂ concentration was fixed at 10% for all the composites. Upon increasing the GNP concentration up to 0.5%, a significant improvement was observed in the compressive strength, microhardness, and electrical conductivity of the composite. Furthermore, the properties were significantly improved by increasing the sintering temperature from 900 to 1000 °C. The compressive strength, hardness, and electrical conductivity of Cu–10%ZrO₂/0.5%GNP were higher than those of the Cu–ZrO₂ nanocomposite by 60, 21, and 23.8%, respectively. This improvement in the mechanical properties is because of the decrease in the crystallite size and dislocation spacing, which increases the dislocation density, thereby increasing the impedance towards dislocation movement. The lower stacking fault energy of the hybrid nanocomposites enables easier electron transfer within and between the Cu grains, resulting in an improved electrical conductivity. The enhancement in strength and electrical conductivity were aided by the GNPs and ZrO₂ nanoparticles that were dispersed widely in the Cu matrix.     

Color tunable Ba3Lu(PO4)3:Tb3+,Mn2+ phosphor via Tb3+→Mn2+ energy transfer for white LEDs

Series of UV excited Ba₃Lu(PO₄)₃:Tb³⁺,Mn²⁺ phosphors with tunable green to red emissions had been prepared using solid state reactions. Powder X-ray diffraction and Rietveld structure refinement were used to investigate the phase purity and crystal structure of the prepared samples. Under UV excitation, the Ba₃Lu(PO₄)₃:Tb³⁺,Mn²⁺ samples exhibited not only the typical Tb³⁺ emission peaks but also the broad emission band of Mn²⁺ ions due to the efficient Tb³⁺→Mn²⁺ energy transfer which had been verified by luminescence spectra and decay curves. Utilizing the Inokuti-Hirayama model, the Tb³⁺→Mn²⁺ energy transfer mechanism was determined to be the electronic dipole–quadrupole interaction. Moreover, the emission spectra of Ba₃Lu(PO₄)₃:0.80Tb³⁺,0.015Mn²⁺ sample at different temperatures manifested that our prepared phosphors possessed good thermal stability. The luminescence properties investigation results revealed the potential value of Ba₃Lu(PO₄)₃F:Tb³⁺,Mn²⁺ in application for UV excited phosphor converted white light emitting diodes.