Cs2V4O11: an easy-to-grow Cs standard

[Brian Joy]

I’ve come across a compound, Cs₂V₄O₁₁, that could serve as a useful Cs standard simply because it’s incredibly easy to produce, is not water soluble, is not hygroscopic, and is only moderately beam-sensitive.  The attached paper provides some details on the structure of Cs₂V₄O₁₁.  The compound contains 43.65 wt% Cs₂O and 56.35 wt% V₂O₅.  When using Cs₂CO₃ and V₂O₅ as starting materials, 47.25 wt% Cs₂CO₃ (dried) and 52.75 wt% V₂O₅ give the proper stoichiometry.  Or one can use 48.07 wt% CsCl (dried) and 51.93 wt% V₂O₅.  If an excess of Cs₂CO₃ or CsCl is added, then CsVO₃ is produced in addition to the target compound.  CsVO₃ is water soluble (though dissolves slowly), and so its presence provides a useful means of loosening the Cs₂V₄O₁₁ crystals, though some chipping may be necessary.  In my run, I used 1.56 g powdered Cs₂CO₃ and 1.48 g powdered V₂O₅, mixed thoroughly with a toothpick.  Although I used an alumina crucible to grow the compound, it would probably be fine to use a porcelain crucible.  The synthesis is outrageously simple:  Just place the mixture in a furnace overnight at ~550°C and then allow it to cool to room temperature within the furnace.  That’s it.  (I cooled the furnace at 5°C per hour for 20 hours, but I don't know that this is necessary.)  In this approach, when using Cs₂CO₃, the volume of the crucible needs to be at least an order of magnitude greater than the volume of the reactants, as the reaction releases CO₂.  The resulting intergrown reaction products are 100% crystalline, and so the yield is high.  The Cs₂V₄O₁₁ is orange-brown, while the CsVO₃ is colorless.  The crystals range up to several mm in length and possess voids previously occupied by CsVO₃ (with very minor remaining CsVO₃ producing bright spots in BSE):



I’ve subjected the material to my usual test of exposure to a focused 15 keV/10 nA beam for ten minutes.  The results, shown below, show that the Cs Lα count rate remains essentially constant for perhaps 150 seconds before starting to drop off. 



With a 30 nA beam current and the beam defocused to 10 microns, the Cs Lα count rate remains steady within counting error.  Note that the apparent slight upward drift in count rate on channel 5 is not present on channel 2.  Regardless, just slight defocusing of the beam (to perhaps 5 microns) at 10 nA should prevent beam damage and yield count rates in the few thousands per second on PET.



Analyzing my pollucite for Cs while assuming a fixed matrix composition produces the results shown below.  Note that Cs L_3,abs is located at ~79.16 mm on PET and at ~172.00 on LiF, so V Kα cannot ionize Cs L₃, but V Kβ can; therefore a small but non-negligible fluorescence correction to Cs Lα must be considered.  This is not the ideal situation, but, then, the correction is less than 0.5%.  Once again, the atomic number correction dominates the matrix corrections.

PAP/MAC30:


Armstrong/FFAST:


WD spectra are shown here:



Note that Cs Lβ₂ interferes at the V Kα peak position using either PET or LiF.

Although I currently regard CsTiOAsO₄ as the Cs standard (and I still want to synthesize CsNbOB₂O₅ and CsMnPO₄), Cs₂V₄O₁₁ is so easy to produce that it shouldn’t be disregarded.

[Probeman]

I’ve come across a compound, Cs₂V₄O₁₁...1_07_18_3_27_38.png[/img]

[snip]

I’ve subjected the material to my usual test of exposure to a focused 15 keV/10 nA beam for ten minutes.  The results, shown below, show that the Cs Lα count rate remains essentially constant for perhaps 150 seconds before starting to drop off. 

Hi Brian,
I don't think that much change in intensity is a problem at all. Even with higher beam currents this can be easily handled, e.g., in Probe for EPMA. Since PFE includes a TDI correction not only for unknowns but also for standards!

 

Nice work!   This could be really useful.

[Brian Joy]

Here is a plot of Cs Lα count rates in Cs2V4O11 using 15 keV/10 nA and with the beam defocused to 5 microns.