DTA and dielectric study of the high temperature phase of Na2SO4

Badr, Y.; El-Kabbany, F.; Tosson, M.

doi:10.1002/pssa.2210530165

Cited by 14 publications

(2 citation statements)

References 7 publications

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“…The dielectric constant measurements were performed using a specially designed cell [5], the temperature of which could be controlled in the range 0 to 1000 "C, with various heating rates. The sample cell system was then connected to a n RLC bridge type PM6302 (Phillips) with capacitance range 0.1 p F to 1000 p F a t frequency 1 kHz.…”

Section: Methodsmentioning

confidence: 99%

Mechanism of thermal hysteresis in reversible transformation of K2SO4

El-Kabbany

1980

Phys. Stat. Sol. (a)

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The reversible phase transformation of potassium sulphate is studied. Differential thermal analysis, dilatometric and dielectric measurements show the occurrence of a reversible phase transition at 571 °C for K2SO4 with heat of transformation H = 2.3 kcal/mol and activation energy E = −215 kcal/mol. The thermal hysteresis in this reversible transformation is examined, the magnitude of the temperature hysteresis does not exceed 5 K. An acceptable agreement is observed between the measured values of the transition temperature obtained by the three different techniques. The dilatometric analysis shows that this transition is accompanied by thermal expansion with a relative thermal expansion coefficient of 6 × 10−3. The mechanism and physical basis for the phenomenon of thermal hysteresis observed in the temperature of the phase transition are proposed and discussed thermodynamically on the assumption that there is a potential barrier between the atomic arrangements of any two phases.

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Section: Methodsmentioning

confidence: 99%

Mechanism of thermal hysteresis in reversible transformation of K2SO4

El-Kabbany

1980

Phys. Stat. Sol. (a)

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“…The obtained crystals were free from visible defects and had well developed (100) faces. The samples are coated with silver paste on two opposite faces, and inserted in a special cell [12] with accuracy of the measuring temperature being about f l K in the temperature range -60°C up to 30°C.…”

Section: Methodsmentioning

confidence: 99%

Electrical and Thermal Properties of NH₄Br_xCI_1‐x Single Crystal

1990

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A b s t r a c t . The effect of partial replacement of C1-ions by Brions in the mixed system of ammonium chloride and ammonium bromide during a set of thermal heating cycles is studicd. The study includes electrical measurements (d.e. resistivity, dielectric constant and the spontaneous thermal current), differential thermal analysis (DTA) and dilatometric thcrmal analysis in the tempera,ture range --6O"C up to 30°C. The results show a large change in the various measured parameters sensitive to thermal agitation process and to the presence of the bromine ions in the mixed crystal system close to the morphotropic boundary x == 0.5. At this boundary the temperature region of the ordered phase extended by about 28°C. The transformation enthalpy was reduced in such case to 41.3 cal/mol. According to the different experimental data of the system NH,Br,CI, --2, a phase diagram was proposed. This phase diagram predicted that the order-disorder phase transition point changed widely according to the value of x and retished -2°C when the mixed crystal system contained 50% of Br-ions. Elektrisehe und thermische Eigenschaften von NH~B1.,C11_,-EinkristallenI n h a l t s i i b e r s i c h t . Der Effckt einer teilweisen Ersetzung von C1--durch Br--Ionen in einem Alischsystem nus Ammoniumchlorid und Ammoniumbromid wjhrend eines Heizzyklusses wird elektrisch (Widerstand, dielektrische Konstante und spontaner Thermstrom), kalorimetrisch und dilatometrisch im Temperaturbereich von -60°C bis 30°C untersucht. Es zeigt sich ein groWer EinflnU thermischer Beweguiigsprozesse und der Bromkonzentration von 50%. Die Ergebnisse werden zu einem Phasendiugranim zusammengefaBt, das die Abhangigkeit des Ordnungs-Unordnnngsiibergangs von der Bromkonzentration unterstreicht. 1:)The values with asterisks are those obtained for ordered phase while the others for the disordered phase.

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Effect of the internal motion of NH4+ on the properties of some halides

Badr

El-Kabbany

Said

et al. 1980

Phys. Stat. Sol. (a)

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The temperature dependence of dc resistivity and dielectric constant for single crystals as well as polycrystalline samples of NH,Cl, and NH,Br show anomalous behaviour in bot,h, the low and high temperature regions. Anomalies in the high temperature region are attributed to the reorientational motion of the NH; ion between two alternative orientations, while a freezing out of the reorientational motion in the low temperature region takes place. The rate of change of dc resistivity is found t.0 be higher than the rats of change of the dielectric constant with temperature. A comparison between the temperature behaviour of dc resistivity, dielectric constant, DTA and TMA data for single crystals and polycrystalline samples show that the activation energy is higher for single crystals. The values of the dc resistivity, and DTA and TMA areas are found to be higher in the case of single crystals as well.Die Tempernturabhlngigkeit der Gleichspannungsleitfahigkeit und der Dielektrizitatskonstante 7eigt sowohl fiirEinkrist,alle als auch fur polykristalline Proben von NH,CI und NH,Br anomales Verhalten soivohl im Bereich t.iefer als auch hoher Temperaturen. Anomalien im Hochtemperaturbereich werden der Reorientierungsbemegung der NH:-Ionen zwischen zwei Orientierungsmoglichkeiten zugeschrieben, wLhrend im Tieftemperaturbereich ein Ausfrieren der Reorientierungsbewegung stattfindet. Es wird gefunden, da13 die Anderungsrate der Gleichspannungsleitflihigkeit hoher ist als die Anderungsrate der Dielektrizitatskonstante mit der Temperatur. Ein Vergleich zwischen dem Temperaturverhalten der Gleichstromleitfiihigkeit, Dielektrizitatskonstante, DTAund TMA-Daten fur Einkristalle und polykristalline Proben zeigt, daB die Aktivierungsenergie fur Einkristalle hoher ist. Die Werte der Gleichstromleitfiihigkeit und der DTA-und TMA-Flachen sind im Falle von Einkristallen ebenfalls hoher.

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DTA and dielectric study of the high temperature phase of Na2SO4

Cited by 14 publications

References 7 publications

Mechanism of thermal hysteresis in reversible transformation of K2SO4

Mechanism of thermal hysteresis in reversible transformation of K2SO4

Electrical and Thermal Properties of NH₄Br_xCI_1‐x Single Crystal

Effect of the internal motion of NH4+ on the properties of some halides

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DTA and dielectric study of the high temperature phase of Na2SO4

Cited by 14 publications

References 7 publications

Mechanism of thermal hysteresis in reversible transformation of K2SO4

Mechanism of thermal hysteresis in reversible transformation of K2SO4

Electrical and Thermal Properties of NH4BrxCI1‐x Single Crystal

Effect of the internal motion of NH4+ on the properties of some halides

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Electrical and Thermal Properties of NH₄Br_xCI_1‐x Single Crystal