Hi all,
All I can think of is an exsolution of some type. But, this seems
difficult to imagine at a low temperature such as this.
- Kurt
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 22, 2007 12:29 PM
To: Jon Wright
Cc: rietveld_l@ill.fr
Subject: Re: peaks splitting
OOOPSSS! True: 006 can't split!
I just overlooked the hkl's of the split peak.
Needless to say, I should have read the message more carefully...
Norberto Masciocchi
Quoting Jon Wright <[EMAIL PROTECTED]>:
> Hi everyone,
>
> Three responses saying it might be a lower spacegroup? I wonder if the
> emperors have their clothes on today?
>
> (006) reflections can't split in R-3c as they only have a multiplicity
> of 2 in the first place (0,0,6 and 0,0,-6). You were lucky enough to
> split (00l) which rules out any lattice distortion. Or lots of people
> are about to shout at me.
>
> Either a paper about "phase segregation" or an experimental artifact
> like a temperature instability. Or both!
>
> Cheers,
>
> Jon
>
> [EMAIL PROTECTED] wrote:
>> Dear all
>> I need your kind help
>> I am investigating a trigonal system. I collected neutron diffraction
>> patterns at T=300K and T=4K.
>> The data at T=300K can be nicely fitted with the spg R-3c.
>> At T=4K again I can described the data with the spg R-3c, but I
>> noticed that now
>> the peaks with a larger c-axis component (see the (006) peak picture
in
>> attachment) are splitted in two: it is like as at low temperature
>> there are two
>> phases with different c-axis (10.5838 and 10.566 Amstrong) and same
a-axis.
>> I don't think that the sample is chemically phase separated because
at room
>> temperature the (006) reflection is clearly a single peak. The
splitting
>> appears only at low temperature.
>>
>> Could anyone suggest me any possible explanation of this splitting
(lattice
>> distortion, modulation, etc)? Could be possible a triclinic
distortion?
>>
>> I don't know how to fit the data at T=4K. Should I change the space
group
>> because now I have two peaks while the R-3c gives me only one peak?
Then by
>> which criteria should I choose the new space group?
>>
>> thank you very very very much for your advices
>>
>>
>> best regards
>>
>> Stefano Agrestini
>>
>> Physics Department
>> The University of Warwick, UK
>>
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>>
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