The thermodynamics and mechanisms of ordering systems

Irani, R. S.

doi:10.1080/00107517208228017

Cited by 17 publications

(2 citation statements)

References 42 publications

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“…There are, in principle, three distinct transformation mechanisms in solids: heterogeneous, homogeneous, and spinodal . The observation of distinct BZT phases here, formed from a single-phase pseudocubic calcined precursor, indicates that heterogeneity develops during the ordering transition.…”

Section: Discussionmentioning

confidence: 73%

In Situ Measurement of Cation Order and Domain Growth in an Electroceramic

et al. 2003

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In situ methods are ideally suited for the study of the development of property-critical structural features during materials processing. As an example of their potential in the area of complex oxide electroceramics, here, we apply in situ synchrotron powder diffraction to investigate the ordering processes responsible for optimizing the microwave dielectric properties of the commercial electroceramic barium zinc tantalate. The collection of synchrotron diffraction data with high resolution and high intensity during processing has allowed the growth of cation site order within a domain and the size of the ordered domains to be separated during the multistage thermal treatment processing used by industry. Domain growth does not commence until the extent of order within a domain is maximized. Analysis of the superstructure intensities with the Avrami equation shows that nucleation is not important in this process. Domain growth then occurs by the curvature-driven Allen-Cahn mechanism. The complex nature of the ordering is confirmed by the coexistence of two phases whose temporal evolution divides into two stages according to the two stages of ordering and domain growth mentioned above. The implications of these observations for industrial processing procedures aimed at reducing the processing time are discussed.

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Section: Discussionmentioning

confidence: 73%

In Situ Measurement of Cation Order and Domain Growth in an Electroceramic

et al. 2003

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“…Other systems where grain-boundary ordering transformations have been observed 8 have involved a change in Bravais lattice with associated distortions.…”

Section: Discussionmentioning

confidence: 97%

Microstructure and Kinetics of the Ordering Transformation in Iron–Cobalt Alloys, FeCo, FeCo–0.4%Cr, FeCo–2.5%V

Buckley¹

1975

Metal Science

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Ordering in FeCo, FeCo-0·4Cr, and FeCo-2·5V is studied using X-ray diffraction, saturation magnetization, and optical and electron microscopy. The kinetics of the disorder to order transformation on isothermal heat-treatment of quenched alloys are determined over the temperature range 250-600°C. Between 500 and 600°C alloys order by a homogeneous process followed by coalescence of antiphase domains. Below I'V 430°C FeCo and FeCo-0·4Cr order by nucleation and growth of ordered regions at grain boundaries, this mechanism does not occur in FeCo-2·5V. The grain-boundary orderedregionsexhibita facetedmorphology.Upon ordering the equiatomic alloy of iron and cobalt changes from the A2 (bcc) to the B2 type of structure. Only a rearrangement of atoms on the same lattice sites occurs, with a very small change in volume (0'2 % expansion) and no compositional changes. A previous experimental study of ordering in this system 1 indicated that the transformation was of the homogeneous type, i.e. the degree of order within the alloy remained uniform during the transformation; however, a network of antiphase domains was formed which coalesced with prolonged annealing. Within the temperature range 400-600°C there was no detectable difference in the kinetics of ordering between the binary alloy and alloys containing up to 2·5 % vanadium with iron and cobalt in equal proportions. However, the kinetics of the subsequent antiphase domain coalescence appeared to be affected by the presence of the ternary additions, particularly at temperatures < I"V 500°C. For the binary alloy the apparent antiphase domain size, as measured by X-ray superlattice line broadening, increased very rapidly with time during isothermal annealing of quenched alloys, the domain size reaching a very large value before ordering was completed. For the ternary alloys with vanadium the antiphase domain size increased only slowly after the alloy was fully ordered. The present work involves the study of the ordering transformation in both binary and ternary alloys at temperatures of between 250 and 600°C with emphasis on the lower temperature regions and the binary alloy. ExperimentalThree alloys were examined, viz. 50 %Fe-50 %Co; 48·8 %Fe-48·8 %Co-2'5 %V; 49·8 %Fe-49'8 %Co-0'4 %Cr. It was found that the third alloy behaved in much the same way as the binary alloy except that it was more easily handled (the binary Paper No. MS 432. Manuscript received 17 May 1974; in final form 22 August 1974. R. A. Buckley, DPhil, is in the Department of Metallurgy, University of Sheffield. METAL SCIENCEalloy was exceedingly brittle). The methods for the preparation of the alloys from elemental materials have been described previously.! For X-ray and metallographic work, discs I"V O' 5 mm thick were quenched from a temperature of 810°C, and isothermal ordering was carried out in a fused-salt bath. Samples for magnetic analysis were cut from the quenched discs.X-ray measurements were made using a Philips diffracto-. meter fitted with diffracted-beam monochromator set for cobalt K a r...

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(101) Order-twinning mode in a CuAuI superlattice

Smith

1976

Phys. Stat. Sol. (a)

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The thermodynamics and mechanisms of ordering systems

Cited by 17 publications

References 42 publications

In Situ Measurement of Cation Order and Domain Growth in an Electroceramic

In Situ Measurement of Cation Order and Domain Growth in an Electroceramic

Microstructure and Kinetics of the Ordering Transformation in Iron–Cobalt Alloys, FeCo, FeCo–0.4%Cr, FeCo–2.5%V

(101) Order-twinning mode in a CuAuI superlattice

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