see the attached paper

Journal of the Korean Physical Society, Vol. 51, No. 2, August 2007, pp. 850853

Hi Zumaira, in addition to previous answer....

I would like to inform you how to calculate the indices Miller of perovksite  materials . Indeed, indices Miller represent the equation of a plane in the space (a, b, and c  are the intercepts of the plane with the x,y,z  axes, respectively).  So, h = 1/a ; k = 1/b ; and l = 1/c ( indices miller : hkl ).  By using Bragg Law : lamda = 2 d(hkl) sin theta(hkl)   and equation of  between d space and indices miller hkl :  1/d^2  = (h^2 + k^2 + l^2)/a^2   if  cubic,   or 1/d^2 = (h^2/a^2) + (k^2/b^2) + (l^2/c^2) if orthorhombic. 

I hope this information will be useful.

regard, 

Rudy Situmeang

Your answer can be found on this website containing really well-prepared lectures:

http://www.xtal.iqfr.csic.es/Cristalografia/index-en.html

Especially on the lecture 4 called 'direct & reciprocal lattices'.

Good luck.

In addition to orthorhombic and cubic symmetry , you can obtain tetragonal symmetry and then you should use the relation:

1/d^2  = h^2/a^2 + k^2/a^2 + l^2/c^2

I hope this will work, please check it out: https://youtu.be/C3S2qEnTlgI