LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 – four new rare earth metal polyselenides with incommensurate site occupancy and displacive modulation
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Christian Graf
Abstract
Crystals of the four new binary rare earth metal polyselenides LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 were obtained by flux reactions. Their two-dimensionally incommensurately modulated structures were solved from X-ray diffraction data. Structure models were established in super space group X4/n(–αβ0)(βα0)00 with modulation wave vectors q1 = –αa* + βb* and q2 = βa* + αb* and the centering vector (0, 0, 1/2, 1/2, 1/2). The unit cell parameters at T = 293 K are a = 4.216(1) Å and c = 17.048(2) Å for LaSe1.85, a = 4.178(1) Å and c = 16.942(3) Å for CeSe1.83, a = 4.123(1) Å and c = 16.792(2) Å for NdSe1.83 and a = 4.080(1) Å and c = 16.672(2) Å for SmSe1.84; the components of the modulation wave vectors are α = β = 0.292(1) for LaSe1.85 and CeSe1.83, and α = β = 0.293(1) for NdSe1.83 and SmSe1.84, respectively. The modulation originates from a site occupancy wave caused by defects in planar selenium layers coupled to a displacive modulation.
© by Oldenbourg Wissenschaftsverlag, München, Germany
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Articles in the same Issue
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- In search of the crystal structure of low quartz
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