X-ray powder diffraction study of synthetic Palmierite, K2Pb(S04)2 Ralph G. Tissot and Mark A. Rodriguez Sandia National Laboratories, Materials Characterization Department 1822, Albuquerque, New Mexico, 87185 Diana L. Sipola and James A. Voigt Sandia National Laboratories, Ceramic Materials Department 1843, Albuquerque, New Mexico, 87185 ABSTRACT Palmierite (K2Pb(S04)2) has been prepared via a chemical synthesis method. Intensity differences were observed when X-ray powder data from the newly synthesized compound were compared to the published powder diffraction card (PDF) 29-1015 for Palmierite. Investigation of these differences indicated the possibility of preferred orientation and/or chemical inhomogeniety affecting intensities, particularly those of the basal (OW) reflections. Annealing of the Pahnierite was found to reduce the effects of preferred orientation. Electron microprobe analysis confirmed KPb:S as 2:1:2 for the annealed Pahnierite powder. Subsequent least–squares refinement and Rietveld analysis of the annealed powder showed peak intensities very close to that of a calculated Palrnierite pattern (based on single crystal data), yet substantially higher than many of the PDF 29-1015 published intensities. Further investigation of peak intensity variation via calculated patterns suggested that the intensity discrepancies between the annealed sample and those found in PDF 29-1015 were potentially due to chemical variation in the K2Pb(S04)2 composition. X-ray powder diffraction and crystal data for Pahnierite are reported for the annealed sample. Pahnierite is TrigonaUHexagonal with unit cell parameters a = 5.497(1)&c= 20.864(2)& space group R-3rn (166), and 2=3. Keywords: Palmierite, x-ray powder diffraction, Rietveld refinement, preferred orientation, synthesis
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X-ray powder diffraction study of synthetic Palmierite, K2Pb(S04)2
Ralph G. Tissot and Mark A. RodriguezSandia National Laboratories, Materials Characterization Department 1822, Albuquerque,New Mexico, 87185
Diana L. Sipola and James A. VoigtSandia National Laboratories, Ceramic Materials Department 1843, Albuquerque,New Mexico, 87185
ABSTRACT
Palmierite (K2Pb(S04)2) has been prepared via a chemical synthesis method. Intensity
differences were observed when X-ray powder data from the newly synthesized
compound were compared to the published powder diffraction card (PDF) 29-1015 for
Palmierite. Investigation of these differences indicated the possibility of preferred
orientation and/or chemical inhomogeniety affecting intensities, particularly those of the
basal (OW) reflections. Annealing of the Pahnierite was found to reduce the effects of
preferred orientation. Electron microprobe analysis confirmed KPb:S as 2:1:2 for the
annealed Pahnierite powder. Subsequent least–squares refinement and Rietveld analysis
of the annealed powder showed peak intensities very close to that of a calculated
Palrnierite pattern (based on single crystal data), yet substantially higher than many of the
PDF 29-1015 published intensities. Further investigation of peak intensity variation via
calculated patterns suggested that the intensity discrepancies between the annealed
sample and those found in PDF 29-1015 were potentially due to chemical variation in the
K2Pb(S04)2 composition. X-ray powder diffraction and crystal data for Pahnierite are
reported for the annealed sample. Pahnierite is TrigonaUHexagonal with unit cell
parameters a = 5.497(1)&c= 20.864(2)& space group R-3rn (166), and 2=3.
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X-ray powder diffraction study of synthetic Palmierite, K2Pb(S04)2
Ralph G. Tissot and Mark A. RodriguezSandia National Laboratories, Materials Characterization Department 1822, Albuquerque,New Mexico, 87185
Diana L. Sipola and James A. VoigtSandia National Laboratories, Ceramic Materials Department 1843, Albuquerque,New Mexico, 87185
I. INTRODUCTION
In order to develop a quantitative standard containing K2Pb(S04)2, synthesis of
this phase was required. Schwartz, Von H. (1966) described both a thermal and aqueous
method of producing a synthetic Pahnierite and Saalfeld Von H. (1973) investigated a
natural occurring Palmierite from Mount Vesuvius, Italy. An aqueous method for
Palmierite synthesis has been developed and is reported here. X-ray powder diffraction
of this synthetic Palmierite revealed intensity differences compared to the current ICDD
Powder Diffraction File (PDF) No. 29-1015. Modeling of the structure from single
crystal data and both Rietveld and least-square refinements also showed differences in
intensity compared to PDF 29-1015. This study examines these differences and shows
that the powder diffraction intensities presented here more closely match with predicted
by modeling and structure refinements. Additionally, we discuss possible reasons for
intensity deviation, including preferred orientation and chemical inhomogeneit y.
II. EXPERIMENTAL PROCEDURES
Sample Synthesis: The synthesis was conducted with a large excess of K to Pb
(4. 19 moles K per mole of Pb) to promote the formation of KzPb(S04)z rather than
PbS04. Fisher Scientific certified A.C.S. Pb(N03)2 and K2S04 salts were used. The salts
were dissolved in deionized water. The individual salt solutions were filtered through
0.45 pm filter paper prior to the reaction, the lead nitrate solution being filtered twice.
The reaction was patched to synthesize 20g K2Pb(S04)2. The Pb(NOs)z solution
TABLE 4. Experimental Conditions for Rietveld refinement of annealed Palmieriteformula weight 483.5728 range for Rietveld refinement (degrees) 15-120
number of reflections in the 2e range 128preferred orientation vector along (003) 0.984(3)overall Temperature parameter B, (A2) 1.99(4)Peak shape function Pearson VII, (4 parameters)Background function Complex polynomial, n=5Temperature (“C) 25R. 0.0724RW. I 0.1256D n n77 *
TABLE 5. Crystal structure data for Palmierite.Crystal System Trigonal/HexagonalSpace Group R-3 m (#166)Formula number in unit cell Z=3
TABLE 6. Positional Parameters for annealed PahnieriteAtom x Y Occ.
K 1/3 2/3 0.46;0(4) 1.01(2)Pb o 0 0 1.03(3)s o 0 0.4033(4) 1o(1) o 0 0.333(2) 1o(2) 0.296 0.148 0.427 1
(003)(015)
I(012) J
(101) (104) (006)
repared ~l--
d
I
) \From 29-1015 i
10 12 14 16 18 20 22 24 26 28 30
Two-Theta (degrees)
FIGURE 1. Comparison of the calculated KzPb(SOJz pattern to observed diffraction data for the as-prepared and annealed powders. An additional pattern generated from the PDF card 29-1015 is also given.
FIGURE 2. SEM micrograph of as-prepared Palmierite particles.
FIGURE 3. SEM micrograph of annealed Pahnierite particles.
. .
456.4
391.2
326.0
-260,6%~>G~=
195.6
130.4
65.2
0.0,,
,
Difference Pattern
■
�im—
37.6 46.8 56,0 65.2 74.4 83.6 92,8 102.0 111.2
2theta (degrees)
).4
FIGURE 4. Rietveld refinement KzPb(SOJz from annealed powder.
Distorted .XC=Q .*Pb-O octahedron
&
Y\/o
so~tetrahedron A K D,, k
a-axis
u
Ic-axis
FIGURE 5. Packing diagram of KzPb(SO& structure showing SOdtetrahedral and distorted PbOGoctahedra.