Effect of heating rate on the responses of CaF2:Cu,CaF2:Tm,CaF2:Dy and CaF2:Mn

Recent development of CaF2:Cu (the most sensitive material for radiation dosimetry) exhibiting a TL glow peak around 270 degrees C similar to that of CaF2:Mn has made it attractive to study the influence of heating rate on the response of CaF2 based TLDs. Influence of heating rate on CaF2:Mn (known to reduce the response with increasing heating rate) was confirmed in view of the reported controversy about other TLDs. Responses of TL glow peaks around 270 degrees C in CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn were studied. Except CaF2:Mn, no other CaF2 based TLD exhibited a reduction in response with increasing heating rate. On the contrary, in some cases a small increase (10-15%) was noted with increasing heating rate from 1 degrees Cs(-1) to 50 degrees Cs(-1). The shape and the position of the glow peak and the parameters derived from the shape of the glow curve appear to have no relation to reduction of TL efficiency at higher heating rates. Apart from the increased probability of non-radiative transitions at higher temperatures, the observed effects have been assigned to the effect of heating rate on the migration of charge carriers released during the TL readout.     

Ion-assisted codeposition of CaF2-rich CaF2-TiO2 composites as infrared-transmitting films

The influence of the TiO(2) concentration (相似文献   

CaF_2∶Mn热释光材料的研究

研究了ＣａＦ２∶Ｍｎ热释光材料的制备方法和发光曲线、剂量响应曲线、响应的时间衰退特性、剂量率响应、能量响应等剂量学特性。结果表明,ＣａＦ２∶Ｍｎ是一种理想的热释光材料,可用于抗辐射加固研究中半导体材料及电子器件辐射吸收剂量的测量     

Fluorine self-diffusion in CaF2 and BaF2

The self-diffusion of F-18 in single crystals of BaF₂ and CaF₂ was measured between 350 and 940°C. The results were in agreement with diffusion coefficients deduced from ionic conductivity studies, and yieldedH's of 1,6 eV for BaF₂ and of 2.0 eV for CaF₂ for intrinsic diffusion. Below 700°C, extrinsic diffusion behaviour was observed in CaF₂ withH=0.9 eV. The formation energy for anion Frenkel defects was estimated to be in the range 2.2 to 3.1 eV. Both anion and cation diffusion rates were increased in CaF₂ doped with SmF₃ as compared with pure CaF₂, indicating an interrelation between anion and cation defects, as observed previously in the related substances, UO₂ and UO_2+x , The migration energy of cations was estimated to be roughly in the range 1.5±0.6 eV. The implications of the results in terms of diffusion mechanisms are discussed and the remaining uncertainties are indicated.Experiments performed in 1968 at CCR Euratom, Ispra, Italy. The present study constitutes part II of a study of fluorine self-diffusion. Part I is concerned with LiF and NaF (see ref. [6]).     

Electrical conductivity of a CaF2-BaF2 nanocomposite

A CaF₂-BaF₂ nanocomposite material has been prepared via 70CaF₂ · 30BaF₂ (mol %) melt solidification. The material has a lamellar structure due to the eutectoid decomposition of the solidified melt. The 500°C ionic conductivity of the composite is 25 and 330 times higher than those of the parent BaF₂ and CaF₂, respectively. The enhanced conductivity of the composite can be understood in terms of the electrical properties of its interfaces. Original Russian Text ? N.I. Sorokin, I.I. Buchinskaya, P.P. Fedorov, B.P. Sobolev, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 234–237.     

Dielectric Properties of Ultrathin CaF2 Ionic Crystals

Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF₂) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF₂ shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO₂, TiO₂, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF₂ is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.     

Congruently-melting compounds of CaF2 · rcRF3

The composition was determined in congruently-melting CaF₂ · r_cRF₃, where R represents either Y or the lanthanons with atomic number Z(R) ≥ Z(Gd). The stoichiometry number r_c is not an integer or a ratio of simple integers. Among the lanthanons, r_c decreases with increasing Z(R). The resulting crystals all show the hexagonal (LaF₃) structure.     

Slip Systems and plastic anisotropy in CaF2

An examination was made of the slip planes activated in high-purity CaF₂ single crystals with various orientations deformed by compression between 20 °C and 600 °C. It was found that 110 was the most difficult and 100 the easiest to activate. These results are compared to results for UO₂ and zirconia.     

Surface distortion features on indented CaF2 cleavages

Surface distortion features around static indents on the cleavages of CaF₂ single crystals have been investigated by multiple beam interference technique. At room temperature microcracks around such indents nucleate at the sinking in regions. Fizeau fringe patterns (around indents at 200° C) revealed a transition from a three-fold to a six-fold material flow.     

Thermoluminescence of terbium sensitised by samarium in CaF2

Thermoluminescence (TL) in sintered CaF2 doped with Tb4O7 has been studied for UV and X-ray irradiation. Three TL glow peaks for the Tb4O7 doped sample appeared in the temperature regions of about (1) 347-353 K, (2) 378-383 K and (3) 453-458 K, when heated at a rate of 20 K min(-1) after UV or X-ray irradiation at room temperature. It has been found that the 378 K peak intensity of the samples co-doped with Tb4O7 and Sm2O3 became stronger when compared with those doped with only terbium or samarium ions, and the TL peaks of (1) 347-353 K and (3) 453-458 K were not observed. The intensity of the 378 K peak of the co-doped sample was 12.9 times that of the sample doped only with Tb4O7. From the TL spectra and the excitation and emission spectra of photoluminescence for the CaF2 doped activators, it is concluded that the TL of Tb3+ ions is sensitised by the existence of Sm3+ ions. The 378 K TL peak may also be suitable for UV radiation dosimetry.     

真空退火对LiF和CaF2薄膜结晶性能的影响

研究了真空退火对玻璃衬底上热蒸发沉积的LiF和CaF2 薄膜的结晶性能的影响。X射线衍射分析结果表明 ,在4 2 0℃温度下 ,随着退火时间的增长 ,LiF薄膜的结晶状况明显改善 ;在 4 6 0℃温度下 ,随着退火时间的增长 ,CaF2 薄膜的结晶状况越来越好     

P2O5与CaF2制备PF5工艺研究

以P2O5与CaF2为原料,采用加热的方法制备PF5气体,并研究了反应温度、反应时间及P2O5和CaF2质量比对PF5产率的影响。结果表明,制备PF5的最佳条件：反应温度控制在280-300℃,反应时间5h,PF5和CaF2质量比为2．5：1。     

Preparation of CaF2 precursors for laser grade crystal growth

The expansion of commercial excimer lasers has increased the need of high-quality optics manufactured from CaF₂. The key technical parameters, affecting the long-term quality of CaF₂ excimer laser optics, are controlled by the purity of the raw material. The new purifying techniques provide 99.99% purity of the starting material which rises up to 99.999% into the grown crystals. However, the techniques are rather expensive which leads to a significant rise in the price of the final crystal product. The present paper describes an alternative highly effective and relatively low-cost technique providing a precise control over a set of preparatory and purifying procedures and crystal growth. Using an original apparatus for electro-chemical grinding of the thermo-broken starting material, the grained product, uncontaminated by unintentional impurities, may be highly purified by two complementary methods to produce precursors used for UV- and laser-grade CaF₂ crystal growth. Received: 20 April 1999 / Reviewed and accepted: June 2, 1999     

乙醇/水复合溶剂中纳米CaF2的沉淀制备及表征

用纯水溶剂和水/乙醇复合溶剂沉淀制备了不同粒径的CaF2纳米粉体.用FSEM和XRD对沉淀粉体的粒径和形貌进行了观测.研究发现,使用复合溶剂减小了产物纳米CaF2的粒径,从纯水溶液制备的51nm减小到1:4复合溶剂的20nm,并且沉淀粒径随复合溶剂中乙醇含量升高而减小.结果表明,复合溶剂是沉淀制备纳米粉体中控制粒径的有效手段.