scholarly journals Structure and Properties of Ln2MoO6 Oxymolybdates (Ln = La, Pr, Nd) Doped with Magnesium

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 611
Author(s):  
Ekaterina Orlova ◽  
Elena Kharitonova ◽  
Timofei Sorokin ◽  
Alexander Antipin ◽  
Nataliya Novikova ◽  
...  
Keyword(s):  
Rare Earth ◽  
Infrared Spectroscopy ◽  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Spectroscopy Data ◽  
Structure And Properties ◽  
Hygroscopic Properties ◽  
Thermogravimetric Studies ◽  
Mg Doped

The literature data and the results obtained by the authors on the study of the structure and properties of a series of polycrystalline and single-crystal samples of pure and Mg-doped oxymolybdates Ln2MoO6 (Ln = La, Pr, Nd) are analyzed. Presumably, the high-temperature phase I41/acd of Nd2MoO6 single crystals is retained at room temperature. The reason for the loss of the center of symmetry in the structures of La2MoO6 and Pr2MoO6 and the transition to the space group I4¯c2 is the displacement of oxygen atoms along the twofold diagonal axes. In all structures, Mg cations are localized near the positions of the Mo atoms, and the splitting of the positions of the atoms of rare-earth elements is found. Thermogravimetric studies, as well as infrared spectroscopy data for hydrated samples of Ln2MoO6 (Ln = La, Pr, Nd), pure and with an impurity of Mg, confirm their hygroscopic properties.

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).

Structure and Bonding of Tribromocadmates, ACdBr3, A = NH4, Rb, Cs, CH3NH3, (CH3)2NH2, (CH3)4N], [H2NNH3, and (H2N)3C. An X-ray Diffraction and 79-81Br NQR Study

1991 ◽  
Vol 46 (12) ◽  
pp. 1063-1082 ◽  
Author(s):  
V. G. Krishnan ◽  
Shi-qi Dou ◽  
Alarich Weiss
Keyword(s):  
Room Temperature ◽  
High Temperature Phase ◽  
Phase Iii ◽  
Line Spectrum ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Single Chain ◽  
Double Chain ◽  
81Br Nqr ◽  
A Chain

Abstract The 79-81Br NQR spectra of tribromocadmates with the cations K⊕, NH4⊕, Rb⊕, Cs⊕, CH3NH3⊕, (CH3)2NH2⊕, (CH3)4N⊕, H2NNH3⊕, and C(NH2)3⊕ were studied as functions of temperature from 77 K on up to T>300 K. CsCdBr3 shows a singlet 81Br NQR spectrum over the whole temperature range studied. [CH3NH3]CdBr3, with one 81Br NQR line spectrum at room temperature, experiences a phase transition at 167 K; below this temperature an 18-line spectrum is observed. In [(CH3)4N]CdBr3 (phase II), at 290 K, a singlet 81Br NQR is present as is in the high temperature phase III (TII.1 , = 390 K); the low temperature phase III (TII,m, = 160 K has a triplet 81Br NQR spectrum. KCdBr3 shows an 81Br NQR doublet spectrum, as do RbCdBr3, [H2NNH3]CdBr3, and [C(NH2)3]CdBr3. 81Br NQR triplets are observed for [(CH3)2NH2]CdBr3 and NH4CdBr3. Several crystal structures were determined (at room temperature). [(CH3)4N]CdBr3: P63/m, Z = 2, a - 940 pm, c = 700 pm, disordered cation, single chain Perovskite with face connected [CdBr6]- octahedra (nearly CsNiCl3-type). [(CH3)2NH2]CdBr3: P21/c, Z = 4, a = 898 pm, 6 = 1377 pm, c = 698 pm, ß = 91.2°, face connected [CdBr3-octahedra single chain Perovskite. NH4CdBr3: Pnma, Z = 4, a = 950 pm, b = 417 pm, c= 1557 pm, with a double chain of condensed [CdBr6]-octahedra, NH4CdCl3-type. [N2H5]CdBr3: P2,/c, Z = 4, a = 395 pm, 6 = 1749 pm,c = 997 pm,ß = 94.2°, double chain polyanion similar to NH4CdBr3. [C(NH2)3]CdBr3: C2/c, Z = 4, a = 778 pm, 6 = 1598 pm, c = 746 pm, ß = 110.2°, a single chain Perovskite with a chain of condensed trigonal bipyramids [CdBr5]. Three types of anion chains of CdBr3 have been observed: Single octahedral chains, face connected; double octahedral chains, edge connected; a trigonal-bipyramidal chain, edge connected. The relation between the crystal structure and the Br NQR is discussed

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

Structural phase transformation and microwave dielectric studies of SmNb1−x(Si1/2Mo1/2)xO4 compounds with fergusonite structure

2015 ◽  
Vol 17 (19) ◽  
pp. 12623-12633 ◽  
Author(s):  
S. D. Ramarao ◽  
V. R. K. Murthy
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
Room Temperature ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Dielectric Studies ◽  
Scheelite Structure ◽  
Structural Phase Transformation ◽  
Microwave Dielectric

Temperature variation powder XRD measurements reveal that SmNbO4 undergoes a phase transition around 800 °C. SmNbO4 possesses a monoclinic fergusonite structure at ambient temperature and a tetragonal scheelite structure above the transition temperature. We report the stabilization of this high temperature phase at room temperature.

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.

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