共查询到19条相似文献,搜索用时 531 毫秒
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本文用差热分析、恒温热处理、X射线衍射等方法,对LiIO_3在常压的相变过程做了进一步的研究。对于LiIO_3的常压相变机制有了较为详尽的了解 。并发现LiIO_3在高温可相对稳定存在三个相:β,η和δ,它们可分别自行熔化,其熔点相应为:432℃,421℃和416℃,从它们的热经历和存在的温度范围,表明其稳定性顺序为β>η>δ。在室温干燥空气中,与α相和β相共存的还有相,相升温放热转变为β相。在α相存在的温区里,相经过长时间热处理并不转变为α相,同时,相转变为β相的温度比α相高。与α→β的情况相同,β对→β也有诱导作用。而且的存在对α→β也有促进作用。θ相(θ_1与θ_2)与γ相一样,是相变过程的中间过渡相。 相似文献
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铝-铜-镓三元系合金相图的室温截面已经用X射线方法测定出来了。室温固相截面包含11个单相(即α, γ2, γ′, δ, ζ1, ζ2, η2, θ, θ′,α铝和镓)相区,14个双相(即α + ζ1, α+ γ2, α + γ′, γ2 + γ′, γ′+ ζ1, γ2+δ, γ′+δ,δ +ζ2, ζ2+η2, η2+θ,η2+ θ′, γ′ + θ′, θ′+ 镓和θ+α铝)相区和9个三相(即α + γ′+ζ1, α+ γ2+ γ′, γ2+ γ′ + δ,γ′ + δ + θ′, δ+ζ2+θ′, ζ2 + η2 + θ′, η2+ θ′ + 镓, η2 +θ + 镓和θ +镓+ α铝)相区。所有单相和三个二元系内室温存在的单相相同,没有新相出现。
关键词: 相似文献
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本文从44个缓冷和淬炼Mn-Ga合金摄取了德拜·谢乐照相,并配合了在富Ga部分的差热分析,初步画出了这个系统的相图。这个系统除纯Ga外共有十个相。Mn在Ga中的固溶度是几乎无可觉察的。α相是Ga在α-Mn中的原固溶体,在室温的固溶度为1.95at%Ga。β相在室温的均匀范围为8.6—19.2at%Ga,这是β-Mn结构,因此可看作是β-Mn的固溶体,由于Ga原子无规地替代了部分Mn原子而这个结构得在室温稳定存在。γ相可分成γ1,γ2,γ3,三部分,γ1是面心立方结构,γ2是面心四方结构,γ3是有序的面心四方结构,与Cu-Au系中的CuAuⅠ同型。在室温下稳定的是γ3,均匀范围为37—45at%Ga,而在高温稳定的却总是γ1。从γ1变到γ2,再从γ2变到γ3的变化是二级相变。有序度随Ga含量的递增而递增,随温度的递升而递降。整个γ相可看作是γ-Mn的固溶体,γ-Mn本身是不可能用淬炼的办法在室温获得的。δ相只存在于高温,可看作是δ-Mn的固溶体。由于Ga原子替代了部分Mn原子,因而δ一Mn结构产生了畸变而有序化。ε相是有序的六角密堆积结构,每个晶胞含8个原子,它是在约820℃从γ相同成份地转变而成的,在室温的均匀范围估计为27一30at%Ga。η相在室温约50—60at%Ga处有一宽广的均匀范围。从520到600℃,它经历一多型性变化,转变为λ相。λ相的相区随温度的递升而向富Mn的一边偏移。η和λ结构都很复杂。在富Ga的一边,存在着三个居间相χ,φ和ω,它们是由包析或包晶反应所形成的。ω相的化合式很可能相当于Mn2Ga9或MnGa5,而φ相则与NiHg4同型,在Mn2.3Ga7.7左右有一狭隘的均匀范围。在室温稳定存在的七个居间相中,β,ε,γ3,X和φ是铁磁性的。铁磁性最强的是Ga含量较富的γ3和φ相。我们测量了其中若干合金的饱和磁化强度与居里温度。
关键词: 相似文献
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应用传输线理论研究了金属薄膜Salisbury屏的反射率频谱特性,得到了Salisbury屏的反射系数公式和带宽系数的表达式.理论和数值分析表明,Salisbury屏的反射频谱是谐振型的;在谐振频率处,反射率的大小仅与金属薄膜的归一化面电阻α有关,而在其他频率处则取决于α和隔离层波阻抗η2.反射率带宽系数Δ取决于反射率的考察值Γα,η2和α.当α→αc,η2→η0时,Δ取得极
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Salisbury屏
反射率
频带宽度
金属薄膜 相似文献
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晶体学室相图与相变研究组 《物理学报》1977,26(5):199-207
本文用差热分析、恒温热处理、室温及高温X射线衍射等方法,对LiIO3晶体的相变问题进行了研究。弄清了升温过程中γ相的本质,它是并没有稳定存在的温度区间,只能在一定温度范围,一定时间内存在的,从α相转变为β相的过渡相。熔态LiIO3的冷凝过程不同于固态升温过程;这里存在着另一些新相——δ相。由于冷凝条件不同,因而结构也不尽相同,这些δ相在继续冷却时大部分转变为α相,但在未转变为α相之前,再度升温时,则转变为β相。从高温X射线衍射发现:差热分析曲线上所示的α←→γ和δ→α的相变温度是出现新相的温度,这时还伴随着大量的原有相的衍射线,随着时间的延长和温度的改变,原来的相才逐渐消失。同时也证实了γ→β的相变过程需要保温时间和β相的下种自催化作用。 相似文献
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P.A. Heiney P.W. Stephens S.G.J. Mochrie J. Akimitsu R.J. Birgeneau P.M. Horn 《Surface science》1983,125(2):539-564
We have performed a detailed X-ray diffraction study of O2 adsorbed on UCAR-ZYX and Le Carbon Lorraine vermicular exfoliated graphite between 15 and 50 K. At least four phases of physisorbed oxygen are found. The monolayer δ phase consists of a centered parallelogram lattice, with the molecular axes parallel to the graphite surface. The data are consistent with a triple point at 26 K. The melting transition at a coverage of one monolayer appears to be first order. At higher coverages the molecules undergo a lying-down to standing-up transition; the higher coverage ζ phase froms an approximately triangular lattice with the molecular axes perpendicular to the graphite surface. Satellite peaks around the (1, 0) Bragg peak indicate, however, that this cannot be a simple triangular lattice; possible explanations include successively incommensurate layers or a sinusoidal density modulation. For coverages in the two-layer region the ζ phase modulation peaks disappear at 37 K, and at 40 K the adsorbed oxygen appears to undergo a first order melting transition into a fluid phase. With increasing coverage, the 2D X-ray diffraction profiles and phase boundaries do not connect smoothly onto those of the 3D α and β phases. At low temperatures (T < 30 K) the ζ phase always coexists with bulk crystallites; for temperatures near the 2D melting transition the 3D peaks are not observable. These data, taken together with the heat capacity results, suggest a wetting transition with only the bilayer lamellar phase or bulk O2 being stable at low temperatures. 相似文献
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《Solid State Ionics》2006,177(35-36):3051-3055
Unusual structural phenomena have been observed through high temperature X-ray diffraction in fast oxide-ion conductor La1.92Ca0.08Mo2O8.96. A demixion process occurs above 640 °C, with calcium segregation leading to the formation of CaMoO4 impurity. It recombines at higher temperature to reform the pure cubic LAMOX phase (β-type disordered form). In addition, at lower temperature, a double reversed β/α/β phase transition (where α is the monoclinic ordered form) is observed. It is due to the metastability of the β-type structure at low temperature. Depending on the thermal history, La1.92Ca0.08Mo2O8.96 can therefore be obtained in either its α or its β form at room temperature. Sample shaping as a pellet with high relative density suppresses the low temperature phase transitions and stabilizes the cubic β form. 相似文献
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S. V. Mel’nikova A. V. Kartashev V. A. Grankina I. N. Flerov 《Physics of the Solid State》2003,45(8):1572-1578
Crystals of ammonium lithium sulfate NH4LiSO4 in α and β modifications are studied, and conditions of their nucleation and growth are determined. The α modification of NH4LiSO4 and α → β phase transitions are investigated using polarized light microscopy, x-ray diffraction, and differential scanning calorimetry in the temperature range 80–530 K. It is found that, depending on the conditions of growth and storage, there exist two temperature ranges (Tα → β ≈ 340–350 and ≈440–450 K) in which the crystals can undergo an α → β reconstructive phase transition. The enthalpy of this transformation depends on the symmetry of the final phase. In the former case (340–350 K), the reconstructive phase transition leads to rapid destruction of the sample. In the latter case (440–450 K), the crystal structure undergoes a slow transformation (recrystallization) without noticeable distortions. The results obtained indicate that no structural phase transition occurs in the α modification of NH4LiSO4 at 250 K. 相似文献
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Tsutomu Asano Tomohiko Yamamoto Mohammad Forhad Mina Yasuna Fujiwara Hiroshi Takahashi Ichiro Hatta 《Journal of Macromolecular Science: Physics》2013,52(1-2):163-175
Isotactic polypropylene consisting of uniaxially oriented P-phase lamellae was crystallized in a temperature gradient. The β → α transition was investigated by simultaneous measurements with differential scanning calorimetry (DSC) and X-ray diffraction using synchrotron radiation (SR). To compare the transition mechanism, the β-phase sample was deformed by rolling it along the direction of the crystallization. During rolling, the β-crystal is deformed by interlamellar and interchain slip, which induces c-axis-oriented molecules along the rolling direction. The melting behavior is changed by the rolling deformation. For the as-grown β-crystal, the DSC thermogram has three peaks: the β-melting endotherm at 150°C, an exotherm by recrystallization into the °-form, and the endotherm at 167°C caused by melting of the recrystallized α-form. After the rolling deformation, the β-endotherm is extinguished by the successive exotherm. Simultaneous X-ray measurements reveal that the β → α transition is shifted to a lower temperature and that the recrystallized α-form has a c-axis-orientation caused by the rolling deformation. In the process of the β→ α transition, higher-order lamellar structure is developed earlier than formation of the crystalline structure. In this study, the heating phenomena, such as the β α transition and thickening of the β- and α-lamellae, are consistently explained by a mechanism involving melting and subsequent recrystallization. 相似文献
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Saba Beg 《Phase Transitions》2015,88(11):1074-1085
Bi4V2O11-δ has been doped with Ce and Cd to study double substitution. The system with various dopant concentrations (0.07 ≤ x ≤ 0.30) was prepared by the standard solid-state reaction method. The correlation between the polymorphism and oxide ion performance was well investigated as a function of temperature and composition with the help of thermal analysis, X-ray diffraction (XRD) and AC impedance spectroscopy. From XRD results it is seen that the high oxide ion conducting tetragonal γ-phase is stabilized for x = 0.17. For the compositions x ≤ 0.10, monoclinic α-phase is retained at room temperature with clear evidence for two successive phase transitions α ? β and β ? γ. For x = 0.13, β ? γ phase transition is seen. However, the existence of order–disorder, γ' ? γ transition was confirmed for x = 0.17. It is seen that the highest low-temperature ionic conductivity at 320 °C is 3.19 × 10?4 S cm?1 which was observed for x = 0.17. 相似文献
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A. P. Kiselev S. Z. Shmurak B. S. Red’kin V. V. Sinitsyn I. M. Shmyt’ko E. A. Kudrenko E. G. Ponyatovskiĭ 《Physics of the Solid State》2006,48(8):1544-1552
The phase transformations occurring in amorphous europium molybdate Eu2(MoO4)3 during annealing at atmospheric pressure are studied using optical spectroscopy and x-ray diffractometry. It is established that the metastable β phase is formed at a temperature of ~550°C, whereas the transition to the stable equilibrium α phase takes place at higher temperatures T ≥ 700°C. The spectral characteristics of the α phase, which differ substantially from those of the amorphous state and the β phase, are measured for the first time. 相似文献
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J. Stepišnik J. Slak R. Blinc L.A. Shuvalov N.R. Ivanov N.M. Schagina 《Solid State Communications》1973,13(8):1053-1055
A comparison of the quadrupole perturbed deuteron magnetic resonance spectra of the α,β, and γ phase of partially deuterated sodium trihydrogen selenite crystals shows that not only in the monoclinic γ but also in the triclinic β phase the deutrons are ordered whereas they are disordered in the α phase. Spin-lattice relaxation time measurements show the existence of slow hindered rotations of the HSeO3 and H2SeO3 groups at high temperatures as well as the existence of an overdamped ferroelectric soft mode which condenses at the paraelectric to ferroelectric transition. 相似文献