Farbe und Konstitution anorganischer Feststoffe (Pigmente)

Color shift inAl2O3⋅xCr2O3solid solutions and the electroneutrality principle

“…3 these changes have already been observed for Cr 3+ concentrations down to 5%. 5,6 The results of this work thus support that the same cause is responsible for the color shift in the Al 2 O 3 · xCr 2 O 3 series and also the distinct color displayed by ruby, emerald, or the chromium spinel. In the case of Cr 3+ -based gemstones the different shape of E R ͑r͒ reflects that the Al 2 O 3 , Be 3 Si 6 Al 2 O 18 , and MgAl 2 O 4 host lattices are not isomorphous.…”

“…Although 50 years ago it was already established that in that series there is a progressive color change from red to green upon increasing the chromium content, 5 the actual origin of this shift is not understood yet. A similar color shift has also been observed along the series of MgAl 2 O 4 · xMgCr 2 O 4 and YAl 2 O 4 · xYCr 2 O 4 mixed crystals 5,6 where crystal structure is also kept.…”

“…[1][2][3] As an example, in the case of insulating solid solutions containing transition-metal cations such as Al 2 O 3 · xCr 2 O 3 ͑0 Ͻ x Ͻ 1͒, CoAl 2 O 4 · xCoCr 2 O 4 , or PbCrO 4 · xPbMoO 4 · yPbSO 4 the color dependence on the composition is used for preparing different inorganic pigments. 2,[4][5][6] Although the change in a given property along a series of insulating mixed crystals is of interest for applications, the main origin of this fact is often not well established. This situation has already been encountered looking at the series of Al 2 O 3 · xCr 2 O 3 mixed crystals which has widely been investigated [5][6][7] and thus can be considered as a model system within the realm of insulating solid solutions.…”

“…2,[4][5][6] Although the change in a given property along a series of insulating mixed crystals is of interest for applications, the main origin of this fact is often not well established. This situation has already been encountered looking at the series of Al 2 O 3 · xCr 2 O 3 mixed crystals which has widely been investigated [5][6][7] and thus can be considered as a model system within the realm of insulating solid solutions. Although 50 years ago it was already established that in that series there is a progressive color change from red to green upon increasing the chromium content, 5 the actual origin of this shift is not understood yet.…”