Phase Transitions in Hoalga

1983 ◽  
Vol 21 ◽  
Author(s):  
M. Doukoure ◽  
D. Gignoux ◽  
F. Sayetat
Keyword(s):  
Thermal Expansion ◽  
Room Temperature ◽  
Magnetic Order ◽  
Magnetocrystalline Anisotropy ◽  
Exchange Interactions ◽  
Thermal Anomaly ◽  
Antiferromagnetic State ◽  
Hexagonal Symmetry ◽  
X Ray ◽  
Magnetic Structures

ABSTRACTHoAlGa is hexagonal at room temperature. It undergoes two magnetic transitions succesively at TN = 32 K from a paramagnetic to a triangular antiferromagnetic state where the Ho moments lie in the basal plane and at Tt = 18 K in the course of which the moments rotate toward c giving rise to a colinear antiferromagnetic arrangement. X-ray experiments performed between 5 and 300 K allow to determine the crystal evolution through the two transitions. The hexagonal symmetry is not lowered through the transitions; this result is compatible with the observed magnetic groups. The thermal expansion curves show a very anisotropic behaviour of the lattice parameters. The “c” parameter shrinks below TN and this anomaly is to be related to the magnetic order. Along a, a positive thermal anomaly appears below 70 K and this can be interpreted by crystal field effects. Stability of magnetic structures is discussed with regard to exchange interactions and magnetocrystalline anisotropy.

Study of thermal properties of Ga0.5In1.5Se3 by differential scanning calorimetry

2021 ◽  
pp. 2150407
Author(s):  
S. I. Ibrahimova
Keyword(s):  
Crystal Structure ◽  
Differential Scanning Calorimetry ◽  
Thermal Properties ◽  
Thermal Effects ◽  
Room Temperature ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Hexagonal Symmetry ◽  
Scanning Calorimetry ◽  
X Ray

The crystal structure and thermal properties of the [Formula: see text] compound have been investigated. Structural studies were performed by X-ray diffraction at room temperature. The crystal structure of this compound was found to correspond to the hexagonal symmetry of the space group P61. Thermal properties were studied using a differential scanning calorimetry (DSC). It was found in the temperature range [Formula: see text] that thermal effects occur at temperatures [Formula: see text] and [Formula: see text]. The thermodynamic parameters of these effects are calculated.

Effects of Vacancies on the Thermal Expansion of Mercury Indium Telluride Crystals

2010 ◽  
Vol 663-665 ◽  
pp. 1008-1011
Author(s):  
Ling Hang Wang
Keyword(s):  
Thermal Expansion ◽  
Room Temperature ◽  
Linear Expansion ◽  
Semiconductor Material ◽  
X Ray ◽  
Temperature Range ◽  
Vertical Bridgman ◽  
Indium Telluride

The thermal expansion of a novel semiconductor material, mercury indium telluride (MIT) grown by vertical Bridgman (VB) method, was measured from room temperature till 573K by two methods, i.e. Macroscopic dilatometric and X-ray measurements. It is found that the macroscopic expansion is quite different from the expansion of the lattice (micro-expansion). The macroscopic expansion is lower than micro-expansion in the temperature range of 303-425.5K and has a minimum of -0.14% linear expansion, while the macro-expansion becomes larger than micro-expansion in the temperature higher than 425.5K. The former may be due to the effects of the existing neutral vacancies. The latter may result from the influence of thermal-activated vacancies on the lattice.

CRYSTAL STRUCTURE, ELECTRICAL CONDUCTIVITY AND THERMAL EXPANSION OF Pr1-xSrxFeO3-δ(0 ≤ x ≤ 0.6)

2012 ◽  
Vol 26 (32) ◽  
pp. 1250174 ◽  
Author(s):  
V. PRASHANTH KUMAR ◽  
Y. S. REDDY ◽  
P. KISTAIAH ◽  
C. VISHNUVARDHAN REDDY
Keyword(s):  
Crystal Structure ◽  
Electrical Conductivity ◽  
Thermal Expansion ◽  
Room Temperature ◽  
Small Polaron ◽  
Linear Thermal Expansion ◽  
Lattice Parameter ◽  
Polaron Hopping ◽  
X Ray ◽  
Perovskite Type

The crystal structure at room temperature (RT), thermal expansion from RT to 1000°C and electrical conductivity, from RT to 600°C, of the perovskite-type oxides in the system Pr 1-x Sr x FeO 3(x = 0, 0.2, 0.4, 0.6) were studied. All the compounds have the orthorhombic perovskite GdFeO 3-type structure with space group Pbnm. The lattice parameters were determined by X-ray powder diffraction. The Pseudo cubic lattice parameter decreases with an increase in x, while the coefficient of linear thermal expansion increases. The thermal expansion is almost linear for x = 0 and 0.2. The electrical conductivity increases with increasing x while the activation energy decreases. The electrical conductivity can be described by the small polaron hopping conductivity model.

Confirmation of the new technique for measuring the linear thermal expansion of silicon

1993 ◽  
Vol 8 (1) ◽  
pp. 36-38 ◽  
Author(s):  
Liu Fengchao
Keyword(s):  
Thermal Expansion ◽  
Room Temperature ◽  
Accurate Determination ◽  
Linear Thermal Expansion ◽  
Linear Expansion Coefficient ◽  
X Ray ◽  
High Purity Silicon ◽  
Different Temperatures ◽  
Better Than

This paper further confirms that the direct measurement of diffraction angles at different temperatures by using the X-ray diffractometer is better than measurement of the lattice parameters for the rapid and accurate determination of the linear thermal expansion of silicon. High purity silicon has the linear expansion coefficient, α= (2.45±0.05) × 10−6/°C at room temperature. This value does not change for doped P-type and N-type silicon.

Polymorphism in Ho2(MoO4)3

2013 ◽  
Vol 28 (S2) ◽  
pp. S33-S40 ◽  
Author(s):  
C. González-Silgo ◽  
C. Guzmán-Afonso ◽  
V. M. Sánchez-Fajardo ◽  
S. Acosta-Gutiérrez ◽  
A. Sánchez-Soares ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Room Temperature ◽  
Linear Expansion ◽  
Negative Thermal Expansion ◽  
Thermal Treatments ◽  
Positive Coefficient ◽  
X Ray ◽  
Expansion Coefficients ◽  
First Time

Two polymorphs of Holmium molybdate, known as β'-phase and γ-phase, were prepared by solid state reaction with different thermal treatments. These polycrystalline samples have been studied for the first time by X-ray thermodiffractometry from room temperature up to 1300 K. We found that the initial β'-phase undergoes a transition to a β-phase and then to a γ-phase. The γ (hydrated)-phase, turns to the γ (dehydrated)-phase and then to the β-phase. Each sequence involves a reversible and an irreversible phase transition for Ho2(MoO4)3. Both polymorphs have remarkable physical properties like nonlinear optics, ferroelectricity and negative thermal expansion. We have calculated the linear expansion coefficients of both phases. We have obtained a positive coefficient for the β'-phase and a negative one for the γ-phase. Moreover, we have made a comparison of the obtained coefficients with previous results for other rare earth molybdates.

Magnetism, electronic spectra, and structure of transition metal alkoxides. II. The preparation and magnetism of iron(III) alkoxides

1966 ◽  
Vol 19 (3) ◽  
pp. 363 ◽  
Author(s):  
RW Adams ◽  
RL Martin ◽  
G Winter
Keyword(s):  
Room Temperature ◽  
Benzene Solution ◽  
Magnetic Moments ◽  
Exchange Interactions ◽  
Metal Alkoxides ◽  
Antiferromagnetic Exchange ◽  
Crystal Data ◽  
Magnetic Susceptibilities ◽  
X Ray ◽  
The Core

The iron(III) alkoxides, Fe(OMe)3, Fe(OEt)3, and Fe(Obun)a have been prepared by a procedure alternative to those previously described in the literature. The trimeric nature of the three compounds in benzene is confirmed by cryoscopy, and preliminary X-ray single crystal data for the ethoxide are consistent with trimeric entities in the solid. The temperature variation of the magnetic susceptibilities for the three compounds follows the Curie-Weiss law between 90 and 300�K but with large values of θ=- 200�K. The unusually low magnetic moments vary markedly with temperature, and at room temperature remain depressed in benzene solution at peer μeff 4.4 B.M. This anomalous behaviour is ascribed to the presence of weak antiferromagnetic exchange interactions within the cluster of iron atoms which forms the core of the trimeric species Fe3(0R)9. The compounds are sensitive both to hydrolysis and to heating. Hydrolysis decreases and pyrolysis increases the magnetic susceptibility. This provides a convenient method for following the progress of both types of reaction.

Behaviors of the Zr–1.0Sn–0.39Nb–0.31Fe–0.05Cr Alloy at High Temperature

2011 ◽  
Vol 399-401 ◽  
pp. 80-84
Author(s):  
Yi Yuan Tang ◽  
Jie Li Meng ◽  
Kai Lian Huang ◽  
Jian Lie Liang
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
High Temperature ◽  
Oxide Film ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thin Oxide Film ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Phase transformation of the Zr-1.0Sn-0.39Nb-0.31Fe-0.05Cr alloy was investigated by high temperature X-ray diffraction (XRD). The XRD results revealed that the alloy contained two precipitates at room temperature, namely β-Nb and hexagonal Zr(Nb,Fe,Cr,)2. β-Nb was suggested to dissolve into the α-Zr matrix at the 580oC. Thin oxide film formed at the alloy’s surface was identified as mixture of the monoclinic Zr0.93O2and tetragonal ZrO2, when the temperature reached to 750oC and 850 oC. The thermal expansion coefficients of αZr in this alloy was of αa = 8.39×10-6/°C, αc = 2.48×10-6/°C.

scholarly journals The thermal expansion of bismuth by X-ray measurements

1934 ◽  
Vol 143 (849) ◽  
pp. 465-472 ◽  
Keyword(s):  
Thermal Expansion ◽  
Melting Point ◽  
Single Crystals ◽  
Room Temperature ◽  
The Other ◽  
Optical Methods ◽  
Lattice Expansion ◽  
X Ray ◽  
Expansion Curve ◽  
Methods Of Measurement

X-ray measurements recently carried out by the author on the lattice expansion of silver and quartz showed that the coefficients of thermal expansion, over the ranges investigated, are the same as those observed for the specimen as a whole using optical methods. Goetz and Hergenrother, on the other hand, from X-ray measurements on the coefficients of thermal expansion of single crystals of bismuth, claimed to have found a large difference between values obtained by the two methods of measurement. A possible explanatiion of this that their accuracy is not sufficient to establish definitely the deviation of the X-ray measurements from the optical expansion curve. The author has since made X-ray measurements on the expansion of the bismuth lattice from room temperature to just below the melting point, and finds no evidence of such a discrepancy as Goetz and Hergenrother record.

Properties Of Epitaxial Cdte On Si(lll) With a (Ca,Ba)F2 Buffer Layer

1987 ◽  
Vol 91 ◽  
Author(s):  
H. Zogg ◽  
S. Blunier
Keyword(s):  
Thermal Expansion ◽  
Buffer Layer ◽  
Room Temperature ◽  
Band Edge ◽  
Structural Quality ◽  
Near Band Edge ◽  
Thermal Expansion Mismatch ◽  
X Ray ◽  
Device Applications ◽  
Near Band Edge Peak

ABSTRACTEpitaxial CdTe has been grown onto Si(lll) wafers by MBE with the aid of a composition graded (Ca,Ba)F2 buffer layer to surmount the large misfit of 19%. Untwinned CdTe layers with smooth surfaces, narrow X-ray lines and strong photoluminescence with a narrow near band edge peak were obtained. The results indicate a comparable structural quality to well known CdTe layers on sapphire, InSb or GaAs used as buffers to grow (Hg, Cd)Te for IR-device applications. In addition, the CdTe layers are near strain free despite a large thermal expansion mismatch. This is most probably due to dislocations which are able to move along the fluoride/Si interface even after growth and down to near room temperature.

The thermal expansion of aluminate- and aluminogermanate-sodalites

1979 ◽  
Vol 43 (327) ◽  
pp. 429-431 ◽  
Author(s):  
C. M. B. Henderson ◽  
D. Taylor
Keyword(s):  
Thermal Expansion ◽  
Expansion Coefficient ◽  
Room Temperature ◽  
Large Cavity ◽  
Chemical Difference ◽  
X Ray ◽  
Stepwise Heating ◽  
Displacive Transformation ◽  
Two Phases ◽  
Expansion Behaviour

SynopsisDiscontinuities occurring in the expansion behaviour of aluminosilicate-sodalites with large cavity anions such as I− and are thought to occur when the coordinate of the cavity cation becomes 0.25 (Henderson and Taylor, 1978). We also suggested that further thermal expansion work could explore how the disposition of sodalites in a diagram such as fig. 4 of Henderson and Taylor relates to the presence or absence of discontinuities.We have now studied the expansion of three more sodalites which were expected to show discontinuities, namely one aluminogermanate-sodalite (Na8(Al6Ge6O24)I2) and two aluminate-sodalites (Sr8(Al12O24)(CrO4)2 and Sr2Ba6(Al12 O24)(SO4)2). Sr8(Al12O24)(CrO4)2 was thought to have an ∼ 9 Å cubic cell at room temperature but the occurrence of broadened and split reflections in our sample suggests that this is not the case. Stepwise heating experiments on our sample showed the presence of a reversible, presumably displacive, transformation at 40±2 °C above which the X-ray reflections were sharp.All three sodalites showed significantly smaller expansion rates than for aluminosilicate-sodalites having similar degrees of structural collapse. The lower mean expansion coefficient (0–500 °C) for Na8(Al6Ge6O24)I2 of 12.5 × 10−6C−1 compared with that for Na8(Al6Si6O24)I2 of 15.1 × 10−6C−1 is particularly significant as the only chemical difference between these two phases is substitution of Ge for Si. In addition none of the three sodalites showed the discontinuities expected and this suggests that the low expansion rates do not allow the cavity cation to reach a coordinate of 0.25 over the temperature range investigated.Our earlier concept of the mechanism of expansion of the sodalite structure assumed that the expansion of the cavity cation-cavity anion bond forced the cavity cations against and between the framework oxygens so untwisting the partially collapsed structure (Henderson and Taylor, 1978). It now appears that this concept was over-simplified and that the expansion characteristics of sodalites depend on the nature of the tetrahedrally coordinated framework cations present as well as on the cavity cations and anions.

Sign in / Sign up

Export Citation Format

Share Document