Transformation cubic-tetragonal

Melting points and the tetragonal-cubic transformations of the rare earth dicarbides... 

The average atom model also affords an examination ofthe effect ofCa concentration on the structure of silicate perovskite. Given that CaSi03 is cubic, we expect (Mgi Ca )Si03 to become cubic for some value of x, even for a static lattice, and to lower the temperature of the predicted temperature induced orthorhombic to tetragonal/cubic transformation. Figure 11 shows the b/a and c/a lattice ratios as functions of. At the low concentrations that are compatible with our miscibility estimates (figure 10), Ca is unlikely to have a substantial effect on the structure of the static lattice. However, the effect of Ca on the critical temperature remains unknown. A full assessment of calcium s effect on the structure of silicate... 

ZnSnAs2, order-disorder transitions take place at a few degrees below the melting point, leading to a tetragonal-cubic transformation. 

Fig. 46. - Practical cases of the course of equilibrium background, Xa,. and actual kinetic degree of traiisformalion, A (dashed), for the variant processes taking place during the tetragonal-cubic transformation of manganese spinels of the composition MnxFe3-s04 for the various levels of manganese content, see the inserted values,. t. in the region from 2.3 to 3.0.

The temperature dependence of nano-sized Ce ri 02 was studied by in situ synchrotron X-ray powder dififractometry. Due to peak broadening for the nano-sized Ce Zr. Og and weak X-ray scattering by oxygen, the reported tetragonal-cubic transformation temperature might be incorrect. 

The tetragonal phase transforms to the cubic fluorite structure at 2584 15 K [68]. This transformation temperature has been found to be dependent on the atmosphere... 

Tetragonal to cubic transformation temperature of rare earth dicarbides (°C). 

The cubic-to-tetragonal phase transformation temperature of various binary dicarbide solid solutions have been measured (McColm et al. 1973, Adachi et al. 1974,1976, 1978, Loe et al. 1976). A typical example is shown in fig. 13. 

As in the mixed rare earth dicarbide systems, the rare earth dicarbides also form a solid solution with uranium dicarbide and there exists a composition dependence of the cubic-to-tetragonal phase transformation for the UC2-LaC2 or the UC2 CeC2 solid solutions (McColm et al. 1972), as well as for the UC2-GdC2 solid solution (Wallace et al. 1964). 

Diffusionless phase transformations do not require the net transport of atoms across a phase boundary. For example, phase transformations involving a change in spin or magnetic moment or certain changes in crystal structure or symmetry do not require diffusional fluxes. Examples of such processes include the martensitic transformation in steel or certain cubic-to-tetragonal phase transformations. 

Guo Q, Zhao Y, Mao WL et al (2008) Cubic to tetragonal phase transformation in cold-compressed Pd nanocubes. Nano Letters 8 972-975... 

Afterwards, above 2300°C, tetragonal zirconia transforms into high-temperature cubic zirconia (i.e., fluorite type) with a mass density of 5500 kg.m and a coefficient of linear thermal expansion of 10.5 x 10 K ... 

Occasionally, solid-solid transformations will be dependent on the specific composition. An example is the tetragonal to cubic transformation in solid solutions of perovskites where Sr or Pb have been substituted for Ba in BaTi03. The transition temperature measured by DTA or DSC wiU be indicative of the extent of substitution. 

Since these substances are isostructural, solid solution formation is easy across the whole series, and the hardness of 50 mol % alloys, Lno.5Lno.5C2, can be considered alongside the observed depression of the cubic-to-tetragonal phase transformation on cooling. It has been shown that the depression in transformation temperature, AT), is related to cell volume difference AV and the shear modulus G for such solid solutions when the dicarbide of smaller cell volume is considered as the solvent and the dicarbide of larger cell volume is dissolved in it the relationship is... 

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