TEM Studies of modulated structures in the monoclinic (B) phase Of CaO-stabilized Dy2O3

1988 ◽  
Vol 46 ◽  
pp. 580-581
Author(s):  
Y. J. Kim ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Rapid Quenching ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Modulated Structure ◽  
Volume Increase ◽  
Modulated Structures ◽  
Temperature Transformation ◽  
Intermediate Rate

Dysprosia (Dy2O3) undergoes a monoclinic (B) to cubic (C) transformation on cooling through 1950°C, which is accompanied by an 8% volume increase and shattering. Minor additions of CaO combined with rapid quenching, however, are able to stabilize the high temperature phase down to room temperature. The similarities with the tetragonal to monoclinic transformation of ZrO2 suggest that it may be a possible high temperature transformation toughener. A sample of 8 mol% CaO was sintered at 1900°C and cooled at an intermediate rate. About 90% of B phase, which invariably had a modulated structure, was retained.From TEM studies of this B phase, it was shown that most of the selected area diffraction (SAD) patterns in different orientations consisted mainly of three types of reflections: (i) major reflections from the monoclinic lattice; (ii) satellites associated with each major reflection; and (iii) split reflections at the middle of the framework of major reflections. Depending on the orientation, (ii) and (iii) were accompanied by twinned reflections. Fig. 1 displays (i) and (iii) type reflections.

HREM studies of modulated structures of the monoclinic (B) phase in CaO-Dy2O3 solid solutions

1990 ◽  
Vol 48 (4) ◽  
pp. 218-219
Author(s):  
Y. J. Kim ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Solid Solutions ◽  
Room Temperature ◽  
Rapid Quenching ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Volume Increase ◽  
Normal Lattice ◽  
Modulated Structures ◽  
Moderate Resolution

Dysprosia (Dy203) undergoes a monoclinic (B) to cubic (C) transformation on cooling through 1860°C, which is accompanied by an 8% volume increase and shattering. Minor additions of CaO combined with rapid quenching, however, are able to stabilize the high temperature phase at room temperature, which is incommensurately modulated. TEM studies revealed the existence of three different modulations: q1 (001-type; λ ≈ 9.0 Å), q2 (200-type; λ ≈ 7.5 Å), and q3 (λ ≈ 40 Å). HREM studies on modulated specimens have been conducted to search for the origin of these modulated microstructures.Fig. 1 shows characteristic modulations in the [010]B orientation. Whereas both q1 and q2 look like normal lattice fringes in moderate resolution TEM images, HREM images indicate that they are actually not strictly linear but somewhat displaced. This discontinuity is more obvious in the HREM images displaying separate q1 and q2 modulations such as q1 in the [110] orientation (Fig. 2) and q2 in the [011] orientation (Fig. 3).

Examination of CaO-Dy2O3 for potential use as a high-temperature transformation toughening System

1988 ◽  
Vol 46 ◽  
pp. 790-791
Author(s):  
M. M. Fleming ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Transformation Toughening ◽  
Stabilized Zirconia ◽  
Two Phase ◽  
Volume Increase ◽  
Partially Stabilized Zirconia ◽  
Temperature Transformation ◽  
Fast Quenching ◽  
Potential Use

Similarities exist between the tetragonal to monoclinic transformation of ZrO2 and the monoclinic (B) to cubic (C) transformation of Dy2O3. On cooling the transformation occurs at 1950°C and is accompanied by an 8 % volume increase which causes shattering of bulk specimens. The transformation can be suppressed, however, by minor additions of CaO. An attempt was made to fabricate a “PSD” analogue to partially stabilized zirconia (PSZ).As-received and chemically precipitated powders of pure Dy2O3 were mixed with CaO (0 to 25 mol%), uniaxially and cold isostatically pressed, sealed in small Mo crucibles and sintered at various temperatures (1900° or 1650°C) and times before cooling or subsequent annealing treatments. Some pellets were annealed in the two phase (B + C) region at 1700°C for 2 hours before quenching. Specimens were examined by XRD, TEM, EDS, HVEM, and STEM.A fast quenching in combination with the =8 mol% CaO additions were found to be essential for retention of the high temperature B phase down to room temperature.

scholarly journals Deformation-induced nanoscale high-temperature phase separation in Co–Fe alloys at room temperature

2007 ◽  
Vol 90 (20) ◽  
pp. 201908 ◽  
Author(s):  
Lai-Chang Zhang ◽  
Mariana Calin ◽  
Flora Paturaud ◽  
Christine Mickel ◽  
Jürgen Eckert
Keyword(s):  
Phase Separation ◽  
High Temperature ◽  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Fe Alloys

ZERO RESISTANCE AT 113 K IN THE (Bi1.9−xPbxSb0.1)Sr2Ca2Cu3Oy SYSTEM (x=0.1, 0.2, 0.3, 0.4)

1989 ◽  
Vol 03 (07) ◽  
pp. 581-584 ◽  
Author(s):  
H.B. LIU ◽  
Z.Q. MAO ◽  
L. ZHOU ◽  
W.J. ZHANG ◽  
J. LU ◽  
...  
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Superconducting Transition ◽  
Zero Resistance

The 110 K superconducting transition in Bi-Pb-Sr-Ca-Cu-O system has been observed by S.M. Green et al.1 However, T c, zero was 107 K. We have achieved zero resistance at temperature 113 K in Bi-Pb-Sb-Sr-Ca-Cu-O system, higher than that of Bi-Pb-Sr-Ca-Cu-O by more than 6 K. At room temperature, this high temperature phase is steady. After several heating-cooling circle, T c, zero decreases slowly.

X-ray powder diffraction investigation of new high temperature polymorphs of CaTeO3 and CaTe2O5

2001 ◽  
Vol 16 (4) ◽  
pp. 205-211 ◽  
Author(s):  
S. N. Tripathi ◽  
R. Mishra ◽  
M. D. Mathews ◽  
P. N. Namboodiri
Keyword(s):  
High Temperature ◽  
Powder Diffraction ◽  
Room Temperature ◽  
Solid Phase ◽  
High Temperature Phase ◽  
Unit Cell ◽  
Stable Phase ◽  
Temperature Phase ◽  
X Ray ◽  
Monoclinic Lattice

X-ray powder diffraction investigation of the new high temperature polymorphs beta- and gamma-CaTeO3 and gamma- and delta-CaTe2O5 and picnometric measurements of the room temperature phases of the two compounds have been carried out. The study led to the elucidation of their unit cell structures and assignment of entirely new lattice types and parameters to the room temperature phases of CaTeO3 and CaTe2O5 in contrast and supersession to the existing structural information. The results are as follows: CaTeO3 has only one stable phase at room temperature and temperatures up to 882 °C, i.e., α- and has a triclinic unit cell with a=4.132±0.003 Å, b=6.120±0.006 Å, c=12.836±0.013 Å, α=121.80°, β=99.72°, γ=97.26°. The first high temperature phase stable between 882 and 894 °C, i.e., β-CaTeO3, has a monoclinic lattice: a=20.577±0.007 Å, b=21.857±0.009 Å, c=4.111±0.002 Å, β=96.15°, while the next phase stable above 894 °C, i.e., γ-CaTeO3, has a hexagonal unit cell with parameters: a=14.015±0.0001 Å, c=9.783±0.001 Å, c/a=0.698. CaTe2O5 has one stable phase at temperatures up to 802 °C, i.e., α-CaTe2O5 with a monoclinic lattice and parameters: a=9.069±0.002 Å, b=25.175±0.007 Å, c=3.366±0.001 Å, β=98.29 °. The first high temperature phase stable in the range 802–845°, i.e., β-CaTe2O5, is monoclinic with unit cell parameters: a=4.146±0.001 Å, b=5.334±0.002 Å, c=6.105±0.002 Å, β=98.362 °; the next higher temperature phase stable over 845–857 °C, i.e., γ-CaTe2O5, has an orthorhombic unit cell with: a=8.638±0.001 Å, b=9.291±0.001 Å, c=7.862±0.001 Å and the highest temperature solid phase stable above 857 °C, i.e., δ-CaTe2O5 has a tetragonal unit cell with a=5.764±0.000 Å, c=32.074±0.020 Å, c/a=5.5637.

Crystal Structure of the High-Temperature Phase of a Compound Sr2ZnWO6

1992 ◽  
Vol 7 (4) ◽  
pp. 226-227 ◽  
Author(s):  
Fu Zhengmin ◽  
Li Wenxiu
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Powder Diffraction ◽  
Room Temperature ◽  
Lattice Parameter ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray ◽  
Cubic System ◽  
Measured Density

AbstractThe crystal structure of the high-temperature phase of Sr2ZnWO6 prepared by air quenching from 1200° C has been determined by means of X-ray powder diffraction. β-Sr2ZnWO6 belongs to the cubic system, with space group Fm3m and a lattice parameter a = 7.9266 Å at room temperature. Its measured density is Dm = 6.93g/cm3, and each unit cell contains four formula weights.

High-temperature phase transitions and domain structures of KLiSO4: studied by polarisation-optics, X-ray topography and liquid–crystal surface decoration

2017 ◽  
Vol 232 (6) ◽  
Author(s):  
Christian Scherf ◽  
Nicolay R. Ivanov ◽  
Su Jin Chung ◽  
Theo Hahn ◽  
Helmut Klapper
Keyword(s):  
Liquid Crystal ◽  
High Temperature ◽  
Room Temperature ◽  
Crystal Surface ◽  
High Temperature Phase ◽  
Phase Iii ◽  
Temperature Phase ◽  
X Ray ◽  
Domain Structures ◽  
Surface Decoration

AbstractThe transitions between the room temperature phase III (space group

scholarly journals Notizen: The Crystal Structure of β-CsReO4, the Room-Temperature Modification of Cesium Perrhenate

1993 ◽  
Vol 48 (5) ◽  
pp. 685-687 ◽  
Author(s):  
Peter Rögner ◽  
Klaus-Jürgen Range
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Single Crystal ◽  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Orthorhombic Distortion ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Cs Ions

The crystal structure of β-CsReO4, the roomtemperature modification of cesium perrhenate, was determined from single-crystal X-ray data as orthorhombic, space group P nma, a = 5.7556(9), b = 5.9964(8), c = 14.310(2) Å and Z = 4.The structure was refined to R = 0.027, Rw = 0.023 for 779 absorption-corrected reflections. It represents an orthorhombic distortion of the tetragonal high-temperature phase α-CsReO4. The structure of β-CsReO4 comprises isolated ReO4 tetrahedra, linked together by Cs ions. The average Re-O distance was found to be 1.714(4) Å.

TEM of Phase Transitions in Tridymite and Cristobalite Based Materials.

2000 ◽  
Vol 6 (S2) ◽  
pp. 358-359
Author(s):  
Gustaaf Van Tendeloo
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Solid State ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Paraelectric Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Extended Defects

We have determined the structure of the paraelectric phase of BaAl2O4, which is a stuffed tridymite, by different TEM techniques and we will describe the phase transition between the ferroelectric room temperature phase and the paraelectric high temperature phase. We have also obtained HREM images of the higly radiation sensitive acristobalite phase of (Si0,9 Ge0,1)O2 and analysed the extended defects in this material.The stuffed tridymite BaAl2O4 is ferroelectric at room temperature and undergoes a paraelectric-ferroelectric (PEFE) phase transition. The transition is reversible, takes place over a wide temperature range (400K-670K) and has a dynamical character. BaAl2O4 is easily obtained by solid state reaction of BaCO3, and A12O4,. The stoichiometric amounts of the initial reagents were mixed, grinded in an agate mortar under acetone and pressed into a pellet. The pellet was annealed in alumina crucibles at 1000 °C and 1300 °C for 40 h in air and furnace cooled.

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