Author Topic: CsTiOAsO4 ("CTA") as a potential Cs standard  (Read 184 times)

Brian Joy

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CsTiOAsO4 ("CTA") as a potential Cs standard
« on: June 09, 2018, 12:25:49 pm »
While following a trail of references related to potential Cs standards, I came across a handful of papers detailing synthesis of CsTiOAsO4 (“CTA”), which is isostructural with RbTiOPO4; I’ve attached those papers.  CTA contains 41.97 wt% Cs2O, 34.23 wt% As2O5, and 23.79 wt% TiO2.  Of course in EDS the Ti K lines interfere with the Cs L lines, but in WDS no interferences are present as long as one takes care in placing the low background offset for Cs La when using PET (likewise for Ti Ka).  I’m continuing to pursue synthesis of SrCs4(PO3)6, but perhaps CTA should be investigated as well.  I might try to synthesize small crystals of it, but I’m definitely not well enough equipped to grow large crystals in quantity.
Brian Joy
Queen's University
Kingston, Ontario
JEOL JXA-8230

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #1 on: June 09, 2018, 12:31:26 pm »
I believe Marc Schrier mentioned this compound to me during our initial discussions on Cs synthesis as a possibility. With such arsenates we were wondering about its potential beam stability...   also there's the toxicity issue.
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #2 on: June 09, 2018, 03:29:57 pm »
I believe Marc Schrier mentioned this compound to me during our initial discussions on Cs synthesis as a possibility. With such arsenates we were wondering about its potential beam stability...   also there's the toxicity issue.

Note that Kunz et al. (1995) also grew isometric CsTiPO5.  They were only able to grow ~50-micron crystals by spontaneous nucleation from a melt cooled slowly from 1050°C to 800°C.  Presumably larger crystals could be grown using these as seeds.
« Last Edit: June 09, 2018, 03:35:48 pm by Brian Joy »
Brian Joy
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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #3 on: June 10, 2018, 08:35:51 am »
I believe Marc Schrier mentioned this compound to me during our initial discussions on Cs synthesis as a possibility. With such arsenates we were wondering about its potential beam stability...   also there's the toxicity issue.

Note that Kunz et al. (1995) also grew isometric CsTiPO5.  They were only able to grow ~50-micron crystals by spontaneous nucleation from a melt cooled slowly from 1050°C to 800°C.  Presumably larger crystals could be grown using these as seeds.

Hi Brian,
I know nothing about crystal growing but if CsTiPO5 is the same as CsTiOPO4 then see this response here:

http://probesoftware.com/smf/index.php?topic=560.msg6674#msg6674

The only stupid question is the one not asked!

Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #4 on: June 10, 2018, 11:39:36 am »
I believe Marc Schrier mentioned this compound to me during our initial discussions on Cs synthesis as a possibility. With such arsenates we were wondering about its potential beam stability...   also there's the toxicity issue.

Note that Kunz et al. (1995) also grew isometric CsTiPO5.  They were only able to grow ~50-micron crystals by spontaneous nucleation from a melt cooled slowly from 1050°C to 800°C.  Presumably larger crystals could be grown using these as seeds.

Hi Brian,
I know nothing about crystal growing but if CsTiPO5 is the same as CsTiOPO4 then see this response here:

http://probesoftware.com/smf/index.php?topic=560.msg6674#msg6674

Hi John,

The family of compounds with formulas ATiOBO4, in which “A” represents an alkali metal or thallium and “B” represents phosphorus or arsenic, has orthorhombic symmetry.  To my knowledge, all attempts to synthesize CsTiOPO4 have failed.  In contrast, CsTiPO5 has isometric symmetry and can be synthesized by spontaneous nucleation from a melt, as was done by Kunz et al. (1995).

I should note that CsTiOAsO4 itself is not likely toxic, as it is insoluble in water.  Of course the As2O5 starting material is quite dangerous.  Owen Neill should be able to speak to the stability of RbTiOAsO4 under the beam, as he accidentally received some of this material when ordering RbTiOPO4 from Marc.
« Last Edit: June 10, 2018, 06:06:34 pm by Brian Joy »
Brian Joy
Queen's University
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #5 on: June 26, 2018, 01:48:36 pm »
I’m making an attempt at growing CsTiOAsO4, roughly following the instructions in the attached patent document under the heading, “Comparative Example A.”  Instead of using a Pt crucible, I’m using a 15 mL alumina crucible lined with Pt foil and have scaled the amounts of starting materials down by a factor of about 75.  I increased the furnace temperature slowly in order to allow any water and carbon dioxide to escape non-destructively.  When I last checked the crucible early yesterday PM after it had been sitting at 500°C for nearly an hour (to calcine the Cs2CO3), everything looked stable.  I allowed the crucible to sit in the furnace at temperature just below 1000°C for 16 hours and am now in the process of slow cooling.  Unfortunately, I have no digital temperature control, and so I simply have to lower the set temperature manually in order to induce crystal nucleation (and it’ll have to sit at constant temperature during nights).  I should have some sort of result by the weekend.  I'll be ecstatic if I can grow even just 0.5 mm crystals, though the patent is aimed at production of large crystals for laser frequency doubling.

I may try to modify another, similar old furnace for use with a digital “PID” ramp/soak controller in conjunction with a solid-state relay.  If anybody has experience with this sort of modification, please let me know how you went about it.
Brian Joy
Queen's University
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #6 on: June 30, 2018, 03:28:16 pm »
I just removed my CTA run from the furnace.  Although the Pt foil appeared undisturbed, unfortunately most of the reactants bubbled out of the foil enclosure and into the enclosing alumina crucible.  This probably occurred relatively early in the run during dehydration and/or calcination.  I’m currently dissolving the Cs arsenate flux in hot water to see if I produced any CTA at all, but I fear that I may just get ~100 mL of aqueous toxic waste.  Thankfully I have a means of disposing of this safely.

As Crystalgrower has noted in another post, I could likely get these runs to go more smoothly if I were working with a Pt crucible.  However, I simply don’t have the funds available to buy one.  Would anyone out there be willing to lend one to me?
Brian Joy
Queen's University
Kingston, Ontario
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #7 on: July 02, 2018, 07:48:54 pm »
It appears that I did in fact produce some CsTiOAsO4 during that last, otherwise disastrous run.  It formed blocky crystals that appear to have fractured either during cooling or during removal of the flux.  In some of the crystals, P substitutes for some of the As, as some Cs phosphate flux was probably left over in the crucible from the previous run (and was supposed to have been isolated from the reactants by the Pt foil).  The BSE image below shows one of the CTA crystals surrounded by fine grains of a variety of other phases, some of them Al-rich; the polish isn't so great, as I was in a hurry.  I’ve evaluated the beam sensitivity of the CTA by subjecting it to my usual test of monitoring the Cs Lα count rate at 15 kV and 10 nA for ten minutes with the beam fully focused.  It appears to hold up under the beam remarkably well.  I probably won’t get a chance to do any quantitative analyses until next week.

I think this one shows some real potential as a quality Cs standard, especially if I can manage to grow larger crystals.  However this will require a Pt crucible and better furnace temperature control.




Brian Joy
Queen's University
Kingston, Ontario
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #8 on: July 03, 2018, 06:01:43 am »
And here are WD and ED spectra.  The tiny peak at ~67 mm on TAP is P Kα.




Brian Joy
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #9 on: July 09, 2018, 07:03:29 pm »
I made a second mount of some of the products from my recent CsTiOAsO4 (“CTA”) run after realizing that the CTA was actually quite coarse and not mixed in with the fine-grained fraction.  In fact it was coarse enough (up to ~2 mm) that I was able to pick out individual grains for mounting.  The BSE image below shows two intergrown grains that contain regions rich in inclusions and also regions that are relatively inclusion-free.  The very dark inclusions are TiO2, and the very bright, tiny ones are Pt metal.  The larger, roughly equant inclusions that are just a little darker than the main phase are a Cs-deficient, nonstoichiometric, likely isometric polymorph that probably nucleated during the early 16-hour soak at ~980°C.  These inclusions probably would have been fully resorbed had I been able to control the cooling rate of the furnace a little better.

After performing quantitative analyses, I find that most CTA grains in the mount contain ~0.25 wt% P2O5 contributed by Cs phosphate residue that was present in the enclosing alumina crucible; some contain higher concentrations of P2O5, and I’ve omitted these from the results that I show below.  In order to avoid relatively large matrix corrections for Ti and As using the standards that I have available, I’ve recalculated the analysis results assuming stoichiometric amounts of TiO2 and As2O5 and assuming substitution of 0.25 wt% P2O5 for As2O5, as is consistent with the original measurements. With this concentration of P2O5, wt% Cs2O should be 42.04 for the stoichiometric compound.  The results are as follows, using my earlier-produced Cs2Co2Al(PO4)3 as a Cs standard:

PAP/MAC30:


Armstrong/FFAST:


Note that the matrix corrections for Cs Lα are small.  In summary, it appears that the material that grew with decreasing temperature does in fact contain a stoichiometric concentration of Cs2O.  In further support of this, it is quite homogeneous in Cs:  the last column ("ratio") in the results above is the Boyd homogeneity index for the 95 measurements that I made.

Note that the CTA crystals should be orthorhombic, but their habit is more suggestive of the isometric system.  The crystals are too thick and contain too many inclusions to get a good sense of whether they are isotropic, and I don’t have enough material for powder XRD.

This sure looks like a promising material, and I should be able to grow larger and more inclusion-free crystals once I improve my synthesis setup.


« Last Edit: July 10, 2018, 05:06:20 pm by Brian Joy »
Brian Joy
Queen's University
Kingston, Ontario
JEOL JXA-8230

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #10 on: July 10, 2018, 09:24:38 pm »
This looks like very promising material for utilizing as seed crystals... too bad the Ti K and Cs L lines overlap, but it shouldn't be a problem with WDS.
« Last Edit: July 10, 2018, 09:26:12 pm by Probeman »
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #11 on: July 11, 2018, 11:56:13 am »
I’ve analyzed my pollucite standard using my recently synthesized CsTiOAsO4 as a Cs standard and assuming a fixed matrix composition aside from Cs2O.  These are the results of 30 analyses:

PAP/MAC30:


Armstrong/FFAST:


Note that the source of the difference in results between the two models is the atomic number correction.  Use of Cs2Co2Al(PO4)3 instead as the Cs standard results in a smaller atomic number correction.  I found that Cs Lα count rate in this latter material was stable over a period of at least 10 minutes when using a 10 nA beam current and with the beam defocused to 10 microns (but was not stable with a focused beam at 10 nA).  I've just started another run to produce more Cs2Co2Al(PO4)3 (intentionally this time) and hope to report on it within the next 10 days or so.
« Last Edit: July 12, 2018, 06:42:45 am by Brian Joy »
Brian Joy
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Brian Joy

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Re: CsTiOAsO4 ("CTA") as a potential Cs standard
« Reply #12 on: July 11, 2018, 02:37:54 pm »
Now this is worth checking out.  Below are the results of a test of exposure of CsTiOAsO4 to a focused 50 nA beam for a period of ten minutes.  I focused the beam as tightly as possible (W filament) and made sure that it was as free of astigmatism as possible.  The absorbed current dropped a little during the test, but Cs Lα count rates remained steady within counting error.  In a secondary electron image collected following the test, I could see only a very faint mark at the point of impact of the beam, and I saw no discoloration or relief at all in reflected light.  This is a pretty robust material!

« Last Edit: July 11, 2018, 04:30:39 pm by Brian Joy »
Brian Joy
Queen's University
Kingston, Ontario
JEOL JXA-8230