The formation of a spinel and a hexagonal ferrite by the thermal transformation of cronstedtite
Abstract
Single crystals of cronstedtite, Fe32+(Fe3+Si)O4(OH)5, have been heated in air at temperatures up to 745°C and the structural transformations investigated using x-ray diffraction.
One polymorph examined transformed at 715°C to a single crystal of a spinel, two others formed hexagonal ferrites, and a further polymorph produced no well-defined structure.
The mechanisms of the transformations from cronstedtite to the spinel and to the ferrite are similar. First, at about 275°C, a ferric form of cronstedtite is formed with a structure very similar to the original polymorph. Between this temperature and 715°C, two mechanisms operate simultaneously in the crystal. The anion arrangement in the matrix of the crystal slowly adopts a close-packed structure appropriate to spinel or a hexagonal ferrite. At the same time, zones, resembling Guinier-Preston zones, are formed which are coherent with the matrix and which have a cation arrangement similar to, but not identical with, that of the spinel or the ferrite. The zones increase in number until, between 650°C and 715°C, the entire crystal (matrix and zones) adopts the spinel or the ferrite structure.
Simple magnetic measurements show that the spinel and ferrite are ferrimagnetic but that the temporary zones show no trace of this effect.
The mechanisms are contrasted with those which occur in the kaolinite-mullite series of transformations.
Artikel in diesem Heft
- The formation of a spinel and a hexagonal ferrite by the thermal transformation of cronstedtite
- Growth of NaCl whiskers on NaCl single crystals
- A condensed way of representing inorganic close-packed structures
- Systematic derivation of inorganic close-packed structures: AX and AX2 compounds, sequence of equal layers
- Die Kristallstruktur von Lanthantrifluorid
- Über Verbindungen vom Anti-LaF3-Strukturtyp
- Atomanordnung und Strukturverfeinerung von Cancrinit
- The crystal structure of YB4
- The crystal structure of rathite-I*
- A phase transition in potassium chromium sulphate alum at low temperature
- Origin of dislocations in solution-grown crystals
- L'oxonium dans certains composés uranifères
- An x-ray study of metal complexes of biguanide
- A preliminary investigation of the structure of mercury dibenzyl
Artikel in diesem Heft
- The formation of a spinel and a hexagonal ferrite by the thermal transformation of cronstedtite
- Growth of NaCl whiskers on NaCl single crystals
- A condensed way of representing inorganic close-packed structures
- Systematic derivation of inorganic close-packed structures: AX and AX2 compounds, sequence of equal layers
- Die Kristallstruktur von Lanthantrifluorid
- Über Verbindungen vom Anti-LaF3-Strukturtyp
- Atomanordnung und Strukturverfeinerung von Cancrinit
- The crystal structure of YB4
- The crystal structure of rathite-I*
- A phase transition in potassium chromium sulphate alum at low temperature
- Origin of dislocations in solution-grown crystals
- L'oxonium dans certains composés uranifères
- An x-ray study of metal complexes of biguanide
- A preliminary investigation of the structure of mercury dibenzyl
