A Cubic Phase Formed in Immiscible Fe/Ag(Cu) System S by Ion Mixing

1993 ◽  
Vol 316 ◽  
Author(s):  
B.X. Liu ◽  
F. Pan ◽  
K. Tao
Keyword(s):  
Metastable Phase ◽  
Cubic Phase ◽  
Alloy Films ◽  
Cubic Structure ◽  
New Phase ◽  
Pure Constituent

ABSTRACTFexAg1-x (x=0.20-0.65) and Fey Cu1-y (y=0.50-0.75) nano-multilayers were prepared by alternative deposition of pure constituent metals. Ion mixing of the multilayers by 200 keV xenon ions at 77K resulted in the formation of a similar metastable phase with a big lattice of cubic structure, when the ion dose exceeded 1×1016 and 1×1015 Xe+/cm2 for Fe/Ag and Fe/Cu systems, respectively. The fraction of the new phase emerged in the alloy films increased with increasing ion dose in both cases.

Synthesis and Structural Transformation of Luminescent Nanostructured Gd2O3:Eu Produced by Solution Combustion Synthesis

2007 ◽  
Vol 1056 ◽  
Author(s):  
Luiz G. Jacobsohn ◽  
Bryan L. Bennett ◽  
Stephanie C. Sitarz ◽  
Ozan Ugurlu ◽  
Ana L. Lima Sharma ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Combustion Synthesis ◽  
Structural Transformation ◽  
Annealing Time ◽  
Solution Combustion Synthesis ◽  
Nanocrystal Size ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Solution Combustion ◽  
Cubic Structure

ABSTRACTIn this work we explore the uniqueness of solution combustion synthesis (SCS) technique to produce luminescent nanostructured materials with metastable phases. We synthesized Gd2O3:Eu with the high-temperature phase and induced phase transformation toward the room temperature phase to investigate the effects of structural transformation on the luminescent properties. SCS is based on exothermic redox reactions that undergo self-sustaining combustion, yielding powders composed of agglomerates of nanocrystals with typical dimensions of tens of nanometers. Synthesis of materials through SCS occurs in conditions far from thermodynamic equilibrium and, due to the high temperatures achieved during combustion, metastable crystallographic phases can be formed. Eu-doped Gd2O3 was obtained with base-centered monoclinic structure and average nanocrystal size of 35 nm as determined by Debye-Scherre analysis. Phase transformation to the cubic structure was induced by isothermal annealing at 1000 oC for up to 152 hrs and followed by x-ray diffraction (XRD). Luminescence excitation and emission spectra were obtained as a function of annealing time. The transformation from monoclinic to cubic structure was followed by the behavior of the (111) monoclinic/(222) cubic intensity ratio. The ratio value for the as-prepared material is 6, decreasing fast to 3 after 5 hrs. annealing, and reaching a value of 0.1 after 152 hrs. Concomitant to the structural transformation, nanocrystal size was followed for both crystalline phases. The average nanocrystal size for the cubic phase increases from 27 to 47 nm from 1 to 152 hrs., respectively. On the other hand, nanocrystals with the monoclinic phase remained with a constant size around 38 nm. Overall, variation in size is small due to the low connectivity among nanocrystals resulting from the low isostatic pressure employed to prepare the pellets, together with the non-uniform shape of the agglomerates. Photoluminescence excitation spectra are dominated by a broad centered near 278 nm and assigned to the O2-Eu3+ charge transfer band. Photoluminescence emission results present the 5D0-7FJ (with J = 0-4) transitions of Eu3+ ions. The behavior of these bands was investigated as a function of annealing time and subsequently related to the structural changes.

A temperature-dependent powder diffraction study of chromium lanthanum nitrate, LaCr(NO3)6·12H2O

2000 ◽  
Vol 15 (1) ◽  
pp. 23-25 ◽  
Author(s):  
A.-E. Gobichon ◽  
J.-P. Auffrédic ◽  
D. Louër
Keyword(s):  
Thermal Decomposition ◽  
Nitric Acid ◽  
Acid Solution ◽  
Powder Diffraction ◽  
Cubic Phase ◽  
Temperature Dependent ◽  
Space Group ◽  
X Ray ◽  
Reaction Atmosphere ◽  
New Phase

The new phase LaCr(NO3)6·12H2O was synthesized from a nitric acid solution. The symmetry is trigonal with the parameters a=10.9564(4) Å and c=16.835(1) Å [V=1750.2(2) Å3, space group R-3]. The thermal decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)6·6H2O [a=12.301(1) Å, space group P213] and the chromate(V) LaCrO4. The reduction of LaCrO4 to LaCrO3 occurred at a temperature depending on the oxygen pressure in the reaction atmosphere.

Synthesis of (SIC)3N4 Films by Ion Implantation

1993 ◽  
Vol 316 ◽  
Author(s):  
C. Uslu ◽  
D. H. Lee ◽  
Y. Berta ◽  
B. Park ◽  
N. N. Thadhani ◽  
...  
Keyword(s):  
Ion Implantation ◽  
Amorphous Layer ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Nitrogen Implantation ◽  
Transmission Electron ◽  
Position Sensitive ◽  
Nitrogen Ions ◽  
Substrate Temperatures ◽  
New Phase

ABSTRACTWe have investigated the synthesis of carbon-silicon-nitride compounds by ion implantation. In these experiments, 100 keV nitrogen ions were implanted into polycrystalline β-SiC (cubic phase) at various substrate temperatures and ion doses. These thin films were characterized in detail by x-ray diffraction with a position-sensitive detector, transmission electron microscopy with chemical analysis, and Rutherford backscattering spectroscopy. The as-implanted samples show a buried amorphous layer at a depth of 170 nm. The peak concentration of nitrogen saturates at approximately 45 at. % with doses above ~9.0×1017 N/cm2 at 860°C. These results suggest formation of a new phase by nitrogen implantation into β-SiC.

scholarly journals Новая тригональная (ромбоэдрическая) фаза SiC: ab initio расчеты, симметрийный анализ и рамановские спектры

2018 ◽  
Vol 60 (10) ◽  
pp. 2022
Author(s):  
Ю.Э. Китаев ◽  
С.А. Кукушкин ◽  
А.В. Осипов ◽  
А.В. Редьков
Keyword(s):  
Ab Initio ◽  
Raman Spectra ◽  
Rhombohedral Phase ◽  
Cubic Phase ◽  
Selection Rules ◽  
Initial Stage ◽  
The Difference ◽  
Si Films ◽  
New Phase ◽  
Sic Film

AbstractA new trigonal (rhombohedral) SiC phase, existence of which was previously theoretically predicted by a symmetry analysis, is studied. It is shown that the phase can be formed during the growth of SiC films by the method of substitution of atoms on the surface of a Si substrate. Ab initio calculations of the crystal structure of a new phase and its Raman spectra are performed by the quantum chemistry method. The difference of the selection rules for the Raman active vibrations for this rhombohedral phase from the selection rules for a cubic phase in the coordinate system aligned with the translation vectors of the rhombohedral phase is established. Series of thin SiC/Si films by annealing time are synthesized by the method of the topochemical substitution of atoms, and their Raman spectra are analyzed. The presence of the spectral line (258 cm^–1), that is close to the line of a new trigonal (rhombohedral) phase calculated by the ab initio method, has been found in the Raman spectra of the samples at the initial stage of the growth of a SiC film, which indirectly confirms its existence.

The Phase Diagram of K3FeF6 to 35 kbar and 600 °C

1977 ◽  
Vol 32 (4) ◽  
pp. 413-415 ◽  
Author(s):  
P. W. Richter ◽  
J. B. Clark
Keyword(s):  
Phase Transition ◽  
Phase Diagram ◽  
Temperature Region ◽  
Tetragonal Phase ◽  
Cubic Phase ◽  
Small Temperature ◽  
Effect Of Pressure ◽  
Low Pressures ◽  
New Phase

The effect of pressure on the tetragonal/cubic phase transition in K3FeF6 was studied to 35 kbar. A new phase which also occurs in K3TiF6, exists over a small temperature region at low pressures. A strong possibility exists that the K3FeF6 tetragonal phase is isostructural with the corresponding phase found for the K3XF6 (X = Ln, Y) compounds.

Texture and Phases in Oxide Films on Zr-Nb Alloys

1994 ◽  
Vol 343 ◽  
Author(s):  
Y. P. Lin ◽  
O. T. Woo ◽  
D. J. Lockwood
Keyword(s):  
Raman Spectroscopy ◽  
Volume Fraction ◽  
Raman Band ◽  
Oxide Films ◽  
Cubic Phase ◽  
Columnar Grains ◽  
Beam Orientation ◽  
Cubic Structure ◽  
Low Volume ◽  
Raman Response

ABSTRACTOxide films, 0.2-2.0 μm in thickness on Zr-2.5Nb and 11 μm thick on Zr-20Nb alloys, formed in steam at 673 K, have been examined using TEM, XRD and Raman spectroscopy. Columnar grains of mostly monoclinic Zr02 in oxide films on Zr-2.5Nb exhibit a dual texture: a fibre mode with an axis close to the 102m pole and a [001]m growth mode with an orientation relationship [100]m // [4510]α and (010)m // (0001)α with the α-Zr metal. In both modes, “tetragonal” (and/or cubic) ZrO2 was present. Raman spectroscopy differentiated two non-cubic “tetragonal” forms of ZrOz within the [001]m growth texture. In thin oxides (0.5 μm or less), this corresponds to the tetragonal ZrO2 observed in ceramic zirconia and is characterised by a Raman band near 260 cm−1. The 278 and related 438 cm−1 Raman bands observed here in some oxide films (and in other Zr corrosion oxides) are attributed to a separate, non-cubic phase structurally related to the tetragonal ZrO2. The intensities of the 278 and 438 cm−1 bands are dependent not only on the amount of this modified-tetragonal phase but also on the oxide texture (related to the metal texture) and the beam orientation. The lack of Raman response from the “tetragonal” ZrO2 within the fibre mode of texture indicates either a low volume fraction or a cubic-like structure. For oxide on Zr-20Nb, XRD and Raman spectroscopy show a mixture of monoclinic and “tetragonal” ZrO2; the Raman results indicate the “tetragonal” ZrO2 has a high crystal symmetry or nearly cubic structure.

Phase transition, lithium ion conductivity and structural stability of tin substituted lithium garnets

RSC Advances ◽  
2016 ◽  
Vol 6 (97) ◽  
pp. 94706-94716 ◽  
Author(s):  
C. Deviannapoorani ◽  
S. Ramakumar ◽  
Mir Mehraj Ud Din ◽  
Ramaswamy Murugan
Keyword(s):  
Phase Transition ◽  
Benzoic Acid ◽  
Structural Stability ◽  
Lithium Ion ◽  
Cubic Phase ◽  
Distilled Water ◽  
Humid Condition ◽  
Cubic Structure ◽  
Lithium Ion Conductivity ◽  
Lithium Garnets

The high Li+ conductive cubic phase (Ia3̄d) Li6.5La3Sn1.5Ta0.5O12 immersed with the solution of benzoic acid and ethanol, distilled water and exposed to humid condition for 2 weeks preserved its high conductive cubic structure (Ia3̄d).

The not so simple cubic structure of PbZr1 − x Ti x O3 (PZT): complex local structural effects in perovskites

2011 ◽  
Vol 67 (6) ◽  
pp. 461-466 ◽  
Author(s):  
Nan Zhang ◽  
Hiroko Yokota ◽  
A. M. Glazer ◽  
P. A. Thomas
Keyword(s):  
Lead Zirconate Titanate ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Lead Zirconate ◽  
Cubic Phase ◽  
Unexpected Result ◽  
Structural Effects ◽  
Simple Cubic ◽  
Piezoelectric Lead Zirconate Titanate ◽  
Cubic Structure

High-resolution neutron diffraction on the important piezoelectric lead zirconate titanate (PZT) has found that oxygen disorder exists well into the cubic phase. This unexpected result shows that within this phase there persists a remnant of the tilted oxygen octahedra present within the room-temperature ferroelectric phase. The result is that the cubic phase, far from having a simple crystal structure, exhibits a more complex local structure than had hitherto been thought.

On the new structural phases in Al65Cu20Cr15 quasicrystalline alloy

1995 ◽  
Vol 10 (8) ◽  
pp. 1905-1912 ◽  
Author(s):  
Varsha Khare ◽  
N.P. Lalla ◽  
R.S. Tiwari ◽  
O.N. Srivastava
Keyword(s):  
Metastable Phase ◽  
Structural Characteristics ◽  
Icosahedral Phase ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Structural Variants ◽  
Simple Cubic ◽  
Face Centered ◽  
Specific Orientation

The quasicrystalline (qc) alloy Al65Cu20Cr15, unlike its Ru- and Fe-bearing counterparts like Al65Cu20Ru15 and Al65Cu20Fe15, is a metastable phase. This qc alloy has been shown to possess several structural variants and curious structural characteristics. We have investigated the qc alloy Al65Cu20Cr15 with special reference to the possible occurrence of new structural variants. TEM exploration of the as-quenched qc alloy has indeed revealed the existence of several new phases. These are (i) body-centered cubic (bcc) (a = 12.60 Å, disordered) and simple cubic (s.c.) (a = 12.60 Å, ordered), which are the 1/1 approximants of the primitive icosahedral phase (i phase); (ii) a twice order-induced modulated cubic phase (bcc, a = 25.20 Å) which has been shown to correspond to 1/1 approximant of the ordered i phase [i.e., face-centered icosahedral (FCI)]; and (iii) real crystalline bcc (a = 8.90 Å) and face-centered cubic (fcc) (a = 17.98 Å) phases possessing a specific orientation relationship with the icosahedral matrix phase. Tentative structural models showing the interrelationships between the bcc/fcc phases have been outlined.

Sign in / Sign up

Export Citation Format

Share Document