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Title: Lead apatites: structural variations among Pb 5( BO 4) 3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite)

Abstract

The crystal structure of four Pb apatite samples, Pb 5(BO 4) 3Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space groupP6 3/mandZ= 2. For this isotypic series,B= P 5+ is pyromorphite,B= As 5+is mimetite andB= V 5+is vanadinite. The ionic radius for As 5+(0.355 Å) is similar to that of V 5+(0.335 Å), and this is twice as large as that for P 5+(0.170 Å). However, thecunit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes,V, are almost equal to each other. No explanation was available for this peculiarc-axis value for mimetite. Structural parameters such as average $$\langle$$B—O$$\rangle$$ [4], $$\langle$$Pb1—O 9$$\rangle$$ [9] and $$\langle$$Pb2—O 6Cl 2$$\rangle$$ [8] distances increase linearly withV (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2—O1 distance, so the O1 oxygen atom interacts with the 6s 2lone-pair electrons of the Pb 2+ cation that causes the Cl—Cl distance (=c/2) to increase to the largest value in the series because of repulsion, which causes thec-axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.

Authors:
;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE - BASIC ENERGY SCIENCES
OSTI Identifier:
1413321
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Synchrotron Radiation (Online); Journal Volume: 25; Journal Issue: 1
Country of Publication:
United States
Language:
ENGLISH
Subject:
lead apatites; pyromorphite; mimetite; vanadinite; structure; chemistry; synchrotron high-resolution powder X-ray diffraction (HRPXRD); Rietveld refinement

Citation Formats

Antao, Sytle M., and Dhaliwal, Inayat. Lead apatites: structural variations among Pb5(BO4)3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite). United States: N. p., 2018. Web. doi:10.1107/S1600577517014217.
Antao, Sytle M., & Dhaliwal, Inayat. Lead apatites: structural variations among Pb5(BO4)3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite). United States. doi:10.1107/S1600577517014217.
Antao, Sytle M., and Dhaliwal, Inayat. 2018. "Lead apatites: structural variations among Pb5(BO4)3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite)". United States. doi:10.1107/S1600577517014217.
@article{osti_1413321,
title = {Lead apatites: structural variations among Pb5(BO4)3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite)},
author = {Antao, Sytle M. and Dhaliwal, Inayat},
abstractNote = {The crystal structure of four Pb apatite samples, Pb5(BO4)3Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space groupP63/mandZ= 2. For this isotypic series,B= P5+ is pyromorphite,B= As5+is mimetite andB= V5+is vanadinite. The ionic radius for As5+(0.355 Å) is similar to that of V5+(0.335 Å), and this is twice as large as that for P5+(0.170 Å). However, thecunit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes,V, are almost equal to each other. No explanation was available for this peculiarc-axis value for mimetite. Structural parameters such as average $\langle$B—O$\rangle$ [4], $\langle$Pb1—O9$\rangle$ [9] and $\langle$Pb2—O6Cl2$\rangle$ [8] distances increase linearly withV (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2—O1 distance, so the O1 oxygen atom interacts with the 6s2lone-pair electrons of the Pb2+ cation that causes the Cl—Cl distance (=c/2) to increase to the largest value in the series because of repulsion, which causes thec-axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.},
doi = {10.1107/S1600577517014217},
journal = {Journal of Synchrotron Radiation (Online)},
number = 1,
volume = 25,
place = {United States},
year = 2018,
month = 1
}
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