Accidental but potentially useful Cs compounds

[Brian Joy]

Two weekends ago, in a failed attempt to synthesize CsZr₂(PO₄)₃, I accidentally produced a Cs compound that shows at least some potential.  I don’t have access to Pt crucibles, so in lieu of this, I lined a 15 mL alumina crucible with Pt foil and then placed it along with the reactants in a furnace at 700°C for 70 hours.  What I didn’t realize was that the platinum would react extensively with the liquid mixture of Cs phosphate and phosphoric acid to produce a distinctively orange Pt-bearing liquid and three crystalline Pt phosphates, two of which are Cs-bearing (the third being PtP₂O₇).  In the BSE image below, the (relatively) large, bright grain to the right is the more Cs-rich of the two.  Based on a set of 23 analyses, I believe it to be Cs₄Pt(III)₆P₈O₃₁, which contains 23.0 wt% Cs₂O.  It grew on the Pt foil as clusters of deep orange-red crystals that have adamantine luster and appear to have hexagonal(?) symmetry though are nearly equant -- they’re actually quite pretty.  Another fractured grain of it is present in the upper left of the BSE image.  Just below that grain is a crystal of the other Cs-Pt phosphate, which, based on a set of six analyses, appears to be Cs₂Pt(II)₆P₈O₂₇.  This one, which contains 13.3 wt% Cs₂O, is less common, has a deep olive-brown color in transmitted light (it’s almost opaque), and has near-metallic luster; when carbon-coated it acquires a distinctive blue tint.  The abundant dark grains in the BSE image are Al(PO₃)₃, which formed due to reaction of the alumina crucible with the liquid after the Pt foil tore due to excessive thinning.

The Cs₄Pt(III)₆P₈O₃₁ appears to be relatively stable under the beam.  When collecting a set of wavelength scans at 15 kV and 50 nA and with the beam defocused to 10 microns, the absorbed current remained constant for about eight minutes before starting to drop.  When I get a chance, I’ll test it in the same manner as I did the pollucite and CsCoPO₄.

I should note that I haven't found any literature at all on Cs-Pt phosphates.  The formulas that I wrote above require more than one type of phosphate anion to be present.  For instance, the more Cs-rich compound would need to contain both P₂O₇ and PO₄ groups.  Alternatively, the formula of each compound could be simplified if the Pt is present in more than one oxidation state.

[Brian Joy]

The Cs₄Pt(III)₆P₈O₃₁ appears to be relatively stable under the beam.  When collecting a set of wavelength scans at 15 kV and 50 nA and with the beam defocused to 10 microns, the absorbed current remained constant for about eight minutes before starting to drop.  When I get a chance, I’ll test it in the same manner as I did the pollucite and CsCoPO₄.

OK, forget about this one.  It looks like a pretty interesting and possibly undocumented compound, but here is what happened when I exposed it to a 10 nA focused beam with energy = 15 keV:

[Probeman]

This reminds me of the "incubation time" effect that Ben Buse and Stuart Kearns have discussed.  At lower beam currents it takes a while for the interaction volume to heat up enough to start the ions migrating to the sub surface charge...

That is why there is a "decontamination/incubation" delay for the TDI acquisition in PFE.  However, Anette von der Handt proposes finding a beam current high enough to get the ions migrating quickly (to avoid this incubation shape), but not too high a beam current, so one can characterize the intensity loss in a linear (log) fashion.