I assume you've looked at pages 123 & 127 (in the thesis) of:

http://usir.salford.ac.uk/30746/1/Stuart_Atkinson_thesis.pdf 

Sm2O3 a = 14.168(2)Å, b = 3.624(2)Å, c = 8.848(2)Å, b = 100.05°, sg C2/m,

Dear Alan

We have tried that too. But the profile is not matching.  We doped Sm2O3 with cerium and the powder pattern was taken.  All look the same. The one I have given here is the pure one. If I can get info about this then I can proceed further.  Thank You in advance

Israel Samuel

Israel, this the same data as in your other question on the same topic, I have answered there. Problem with your data density.

The pattern you have provided is that of Samarium Hydroxide Chloride [Sm(OH)2Cl]

Crystal system: Monoclinic

Space group: P21/m

a (Å): 6.1600

b (Å): 3.8000

c (Å): 6.7400

Alpha (°): 90.0000

Beta (°): 112.1700

Gamma (°): 90.0000

ICSD Collection Code: 020491

Reference: Klevtsova, R.F., Glinskaya, L.A., Zh. Strukt. Khim., 10, 494, (1969)

first, you need to further check there is not impurity phase, then you can index the pattern which space group it corresponding to. In fact, the structure of the Sm2O3 was reported inthe  ICSD. Therefore , I uncertain whether your sample is pure one.