# Need information

## Main Question or Discussion Point

need urgent information

Dear All,

Can anyone inform me the following things on urgent basis ?

- The crystal structure of Bi2Te3 is Rhombohedral or Hexagonal ?
- How can I calculate the grain size from the XRD data/curve for Bi2Te3 ?
- how to calculate the lattice parameter of Bi2Te3 (Rhombohedral/Hexagonal crystal structure) from the XRD data/curve ?

Providing such information would be very much helpful to me.

Sincerely
Mahedi

drizzle
Gold Member

not so sure about your first question, Bi2Te3 can posses both structures..
to calculate the grain size [g]:
g=0.9λ/Bcosθ
where,
0.9 is the shape factor
λ is the wavelength of the Cu Kα1 radiation [λ =1.5406×10-10 m]
B is the band width at half maximum [BWHM], and here’s how to get it:
in the diffraction pattern and at an exact Bragg angle, find the maximum intensity value, divide it by 2, you would have 2 points with the same value on both sids of the peak [illustrated below]:
http://img12.imageshack.us/img12/5416/31327198.png [Broken]

B= 2θ2-2θ1 [B should be measured in Radians]

To find the lattice parameters, you use two equations
1] Bragg’s law:

n λ= 2d(hkl)sinθ
set n=1

2] the function that describe the inter-planar distance [d] as a function of the unit cell parameters and Miller indices, h, k and l. i.e. in the case of the hexagonal system:

1/d2(hkl)=4/3[h2+hk+k2]/a2 + l2/c2

hope I’m helping, good luck.

Last edited by a moderator:

Dear Sir,
Thanks for your kind information regarding my inquiry. Sorry for late reply as I was in vacation.