TY - JOUR

T1 - Morphology and Optical Properties of Precipitated Vivianite, Fe3(PO4)2·8H2O

AU - Madsen, Hans Erik Lundager

PY - 2020/6/1

Y1 - 2020/6/1

N2 - Crystals of vivianite, Fe3(PO4)2∙8H2O, belonging to the monoclinic prismatic class 2/m , are grown by precipitation from aqueous solution at temperatures from 25 to 56 °C. At 25 °C aggregates are dominating, but at 35 °C and above single crystals are more common, being tabular along {010} and most often with parallelogram outline; in a few cases twins are observed. The outline is distinct and consistent with published lattice parameters, but at low temperature the {010} faces are very rough as judged from interference colors seen in the polarizing microscope. Lateral faces belonging to the {110} form are visible on crystals grown at 45 and 56 °C, and the widths of their projections on {010} as measured with a micrometer eyepiece served for estimating crystal thickness, making use of the face angle from lattice parameters. Optical parameters are determined by a combination of three methods: 1) measurement of birefringence with an Ehringhaus 6λ compensator, 2) Kamb's method for the optic axis angle determined by the angle‐of‐flight method in conoscopic illumination, and 3) visual interferometry using a polarizing microscope incorporating a Mach–Zehnder interference device. Reasonably precise values of principal refractive indices in the expected range are found.

AB - Crystals of vivianite, Fe3(PO4)2∙8H2O, belonging to the monoclinic prismatic class 2/m , are grown by precipitation from aqueous solution at temperatures from 25 to 56 °C. At 25 °C aggregates are dominating, but at 35 °C and above single crystals are more common, being tabular along {010} and most often with parallelogram outline; in a few cases twins are observed. The outline is distinct and consistent with published lattice parameters, but at low temperature the {010} faces are very rough as judged from interference colors seen in the polarizing microscope. Lateral faces belonging to the {110} form are visible on crystals grown at 45 and 56 °C, and the widths of their projections on {010} as measured with a micrometer eyepiece served for estimating crystal thickness, making use of the face angle from lattice parameters. Optical parameters are determined by a combination of three methods: 1) measurement of birefringence with an Ehringhaus 6λ compensator, 2) Kamb's method for the optic axis angle determined by the angle‐of‐flight method in conoscopic illumination, and 3) visual interferometry using a polarizing microscope incorporating a Mach–Zehnder interference device. Reasonably precise values of principal refractive indices in the expected range are found.

U2 - 10.1002/crat.v55.6

DO - 10.1002/crat.v55.6

M3 - Journal article

VL - 55

JO - Journal of Crystal Growth

JF - Journal of Crystal Growth

SN - 0022-0248

IS - 6

M1 - 1900226

ER -