pseudotetragonal

Pseudotetragonal refers to a crystal structure that appears tetragonal but is actually a lower symmetry, typically monoclinic or orthorhombic. This apparent tetragonal symmetry arises because the deviation from true tetragonal symmetry is very small, or because the domain structure within the crystal effectively averages out the lower symmetry in macroscopic observations.

In crystallography, tetragonal crystals are characterized by having three mutually perpendicular axes of unequal length, with the unique axis being longer or shorter than the other two, which are equal. This results in a unit cell with a square base and a height perpendicular to it. A pseudotetragonal structure, however, may have a unit cell that is slightly distorted from this ideal arrangement. For example, in a monoclinic system, two axes might be nearly equal and perpendicular, with the third axis inclined, but the inclination angle is very close to 90 degrees. Similarly, in an orthorhombic system, all three axes might be nearly equal and perpendicular, but with very small differences in their lengths.

The observation of pseudotetragonal symmetry often depends on the resolution of the measurement technique. X-ray diffraction, for instance, can often distinguish between true tetragonal symmetry and its pseudomorphic forms by detecting subtle differences in peak positions or intensities. However, under certain experimental conditions or with less precise methods, the structure might be misinterpreted as tetragonal. This phenomenon is important in materials science, particularly in studies of phase transitions and ferroelectric or ferromagnetic materials where subtle distortions can significantly impact properties. Understanding the true, lower symmetry of pseudotetragonal materials is crucial for accurate characterization and for predicting their physical behavior.