scholarly journals Thermal Expansion of MgTiO3 Made by Sol-Gel Technique at Temperature Range 25–890 °C

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 887 ◽  
Author(s):  
Tamir Tuval ◽  
Brian A. Rosen ◽  
Jacob Zabicky ◽  
Giora Kimmel ◽  
Helena Dilman ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Sol Gel ◽  
Lattice Parameters ◽  
Published Data ◽  
Temperature Structure ◽  
Solid State Method ◽  
Synthesis Technique ◽  
Thermal Expansion Coefficients ◽  
Reported Data

MgTiO3 is a material commonly used in the industry as capacitors and resistors. The high-temperature structure of MgTiO3 has been reported only for materials synthesized by the solid-state method. This study deals with MgTiO3 formed at low temperatures by the sol-gel synthesis technique. Co-precipitated xerogel precursors of nanocrystalline magnesium titanates, with Mg:Ti ratio near 1:1, were subjected to thermal treatment at 1200 °C for 5 h in air. A sample with fine powders of MgTiO3 (geikielite) as a major phase with Mg2TiO4 (qandilite) as a minor phase was obtained. The powder was scanned on a hot-stage X-ray powder diffractometer at temperatures between 25 and 890 °C. The lattice parameters and the atomic positions of the two phases were determined as a function of temperature. The thermal expansion coefficients of the geikielite were derived and compared with previously published data using the solid-state synthesis technique, providing insights on trends in materials properties at elevated temperature as a function of synthesis. It was found that the deviation of the present results in comparison to previously reported data do not originate from the method of synthesis but rather from the fact that there is an asymmetric solubility gap in geikielite. The lattice parameters of this study present the property of stoichiometric MgTiO3 and are compared to previously reported non-stoichiometric MgTiO3 with excess of Ti. The values of lattice parameters of the non-stoichiometric versus temperature of geikielite found the same for both solid-state reaction and sol-gel products.

scholarly journals Temperature-dependent structural behaviour of samarium cobalt oxide

2017 ◽  
Vol 32 (S2) ◽  
pp. S38-S42
Author(s):  
Matthew R. Rowles ◽  
Cheng-Cheng Wang ◽  
Kongfa Chen ◽  
Na Li ◽  
Shuai He ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Cobalt Oxide ◽  
Sol Gel ◽  
Linear Thermal Expansion ◽  
Rietveld Analysis ◽  
Structural Behaviour ◽  
Temperature Dependent ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Sol Gel Synthesis

The crystal structure and thermal expansion of the perovskite samarium cobalt oxide (SmCoO3) have been determined over the temperature range 295–1245 K by Rietveld analysis of X-ray powder diffraction data. Polycrystalline samples were prepared by a sol–gel synthesis route followed by high-temperature calcination in air. SmCoO3 is orthorhombic (Pnma) at all temperatures and is isostructural with GdFeO3. The structure was refined as a distortion mode of a parent $ Pm{\bar 3}m $ structure. The thermal expansion was found to be non-linear and anisotropic, with maximum average linear thermal expansion coefficients of 34.0(3) × 10−6, 24.05(17) × 10−6, and 24.10(18) × 10−6 K−1 along the a-, b-, and c-axes, respectively, between 814 and 875 K.

Assessment of phase transition and thermal expansion coefficients by means of secondary multiple reflections of Renninger scans

2019 ◽  
Vol 52 (6) ◽  
pp. 1271-1279
Author(s):  
Adenilson O. dos Santos ◽  
Rossano Lang ◽  
José M. Sasaki ◽  
Lisandro P. Cardoso
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Structural Phase ◽  
Angular Position ◽  
Lattice Parameters ◽  
Rochelle Salt ◽  
Multiple Reflections ◽  
Multiple Diffraction ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

This paper reports the successful extension of the basis of the X-ray multiple diffraction phenomenon in the assessment of structural phase transitions and the determination of thermal expansion coefficients along three crystallographic directions, using synchrotron radiation Renninger scans. Suitable simultaneous four-beam cases have accurately resolved the lattice-parameter variation in a nearly perfect single-crystal Rochelle salt using a high-stability temperature apparatus. Secondary reflections observed in the Renninger patterns, chosen by their sensitivity to the shifts in angular position as a function of temperature, have allowed the detection of a monoclinic to orthorhombic phase transition, as well as subtle expansions of all the basic lattice parameters, i.e. without having to carry out measurements on each crystal axis. The thermal expansion coefficients have been estimated from the linear fit of the temperature dependence of the lattice parameters, and are in agreement with those reported in the literature.

Negative Thermal Expansion of Yb2Mo3O12 and Lu2Mo3O12

2008 ◽  
Vol 368-372 ◽  
pp. 1662-1664 ◽  
Author(s):  
X.L. Xiao ◽  
M.M. Wu ◽  
J. Peng ◽  
Y.Z. Cheng ◽  
Zhong Bo Hu
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Solid State Reaction ◽  
Linear Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Orthorhombic Structure ◽  
Conventional Solid State Reaction ◽  
Temperature Range ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Compounds Yb2Mo3O12 and Lu2Mo3O12 were prepared by conventional solid-state reaction. Their crystal structures and thermal expansion properties were investigated. It was found that Yb2Mo3O12 and Lu2Mo3O12 adopt orthorhombic structure and show negative thermal expansion (NTE) in the temperature range of 200-800 °C. Their a-axis and c-axis exhibit stronger contraction in the temperature range of 200-800 °C, while b-axis slightly expands in the temperature range of 200-300 °C and then contracts in the temperature range of 300-800 °C. The linear thermal expansion coefficients al of Yb2Mo3O12 and Lu2Mo3O12 are −5.17 × 10−6 °C−1 and −5.67 × 10−6 °C−1, respectively.

scholarly journals Extraordinary anisotropic thermal expansion in photosalient crystals

IUCrJ ◽  
2020 ◽  
Vol 7 (1) ◽  
pp. 83-89 ◽  
Author(s):  
Khushboo Yadava ◽  
Gianpiero Gallo ◽  
Sebastian Bette ◽  
Caroline Evania Mulijanto ◽  
Durga Prasad Karothu ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Metal Complexes ◽  
Single Crystals ◽  
Room Temperature ◽  
Volumetric Thermal Expansion ◽  
Anisotropic Thermal Expansion ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Multifunctional Properties

Although a plethora of metal complexes have been characterized, those having multifunctional properties are very rare. This article reports three isotypical complexes, namely [Cu(benzoate)L 2], where L = 4-styrylpyridine (4spy) (1), 2′-fluoro-4-styrylpyridine (2F-4spy) (2) and 3′-fluoro-4-styrylpyridine (3F-4spy) (3), which show photosalient behavior (photoinduced crystal mobility) while they undergo [2+2] cycloaddition. These crystals also exhibit anisotropic thermal expansion when heated from room temperature to 200°C. The overall thermal expansion of the crystals is impressive, with the largest volumetric thermal expansion coefficients for 1, 2 and 3 of 241.8, 233.1 and 285.7 × 10−6 K−1, respectively, values that are comparable to only a handful of other reported materials known to undergo colossal thermal expansion. As a result of the expansion, their single crystals occasionally move by rolling. Altogether, these materials exhibit unusual and hitherto untapped solid-state properties.

Structural Disorder and Thermal Dilatation Behavior in Cr-Doped Mullite

1994 ◽  
Vol 346 ◽  
Author(s):  
M.P. Villar ◽  
J.M. Geraldia ◽  
L. Gago-Duport
Keyword(s):  
Thermal Expansion ◽  
Diffraction Data ◽  
Chromium Content ◽  
Sol Gel ◽  
Structural Disorder ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
X Ray ◽  
Anisotropic Expansion ◽  
Thermal Dilatation

ABSTRACTLattice parameters of some different chromium-doped mullites obtained by a sol-gel route and sintered at 1650° C have been determined from X-Ray Diffraction data as a function of both temperature and Cr contents. Profile refinements on the X-ray diffraction diagrams have been carried out, showing that, at temperatures between 800° and 1535° C, an anisotropic thermal expansion takes place for the a and b lattice parameters of the Cr-doped mullite. We show that this anisotropic expansion is dependent on the temperature increase and the chromium content for the different compositions of the mullite crystals.

STUDY ON SYNTHESIS AND EVOLUTION OF NANOCRYSTALLINE Mg4Ta2O9 BY AQUEOUS SOL–GEL PROCESS

2012 ◽  
Vol 19 (03) ◽  
pp. 1250024 ◽  
Author(s):  
H. T. WU ◽  
C. H. YANG ◽  
W. B. WU ◽  
Y. L. YUE
Keyword(s):  
Electron Microscopy ◽  
Solid State ◽  
Sol Gel ◽  
Phase Evolution ◽  
Solid State Method ◽  
Conventional Solid State Method ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
State Method ◽  
Size And Morphology

Nanosized and highly reactive Mg4Ta2O9 were successfully synthesized by aqueous sol–gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg4Ta2O9 was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol–gel process showed great advantages over conventional solid-state method and Mg4Ta2O9 nanopowders with the size of 20–30 nm were obtained at 800°C.

Thermal Expansion and Oxidation of Calcium Oxysulfides by Diffusion

2006 ◽  
Vol 258-260 ◽  
pp. 316-321 ◽  
Author(s):  
Evgeny N. Selivanov ◽  
R.I. Gulyaeva ◽  
V.M. Chumarev ◽  
N.I. Selmenskikh
Keyword(s):  
Thermal Expansion ◽  
Inert Atmosphere ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
Thermal Expansion Coefficients ◽  
Limiting Stage ◽  
Reacting Mixtures ◽  
Iron And Zinc

The iron and zinc calcium oxysulfides Ca3Fe4S3O6, CaFeSO and CaZnSO are synthesized by reacting mixtures of CaO and FeS or of CaO and ZnS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by X-ray microanalysis and X-ray diffraction. From the temperature-dependent lattice parameters of oxysulfides (measured up to 1170K) their thermal expansion coefficients are evaluated. Oxidation Ca3Fe4S3O6 and CaZnSO are studied by thermogravimetric analysis when air heated. Oxidation speed temperature coefficients showing that process limiting stage is diffusion are determined.

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