 Chemistry Help Forum Cubic perovskite bond distances and tolerance factor
 User Name Save? Password

 Undergraduate Chemistry Forum Ask your undergraduate chemistry questions here.

 Thread Tools Display Modes Dec 30th 2014, 12:21 PM #1 elt2112 Junior Member   Join Date: Dec 2014 Posts: 1 Cubic perovskite bond distances and tolerance factor If an ideal cubic perovskite ABO3 has cell parameter 3.905 angstroms, how would I work out the A-O and B-O bond distances for this compound? I thought maybe halving the cell parameter would give the B-O distance, and finding out the diagonal of the cube and halving it would give the A-O bond distance. The question then asks me to calculate the tolerance factor, which I know is t = (rA + rO)/sqrt.2(rB + rO) but how would I work out the radii having only been given the unit cell parameter?   Jan 9th 2015, 03:46 AM #2 MGW1248 Junior Member   Join Date: Jan 2015 Posts: 2 inter atomic bond distance in cubic system = a * SQRT(deltax^2 + deltay^2 + deltaz^2) where x y and z are the co ordinates of the atoms in the unit cell ABO3 perovskite will have 8 A cations on each corner (8 x 1/8 = 1) 1 B cation in the centre (0.5, 0.5, 0.5) 6 O anions, one on each face (6 x1/2 =3) A-O distance is therefore 3.905A * SQRT(0.5^2 + 0.5^2 + 0^2) = 2.761A (assuming you use A = (0,0,0) and O =(0.5,0.5,0) B-O distance is 3.905A * SQRT(0^2 + 0^2 + 0.5^2) = 1.9525A (assuming you use B = (0.5,0.5,0.5) and O = (0.5,0.5,0)   Jan 9th 2015, 04:11 AM   #3
MGW1248
Junior Member

Join Date: Jan 2015
Posts: 2  Originally Posted by elt2112 The question then asks me to calculate the tolerance factor, which I know is t = (rA + rO)/sqrt.2(rB + rO) but how would I work out the radii having only been given the unit cell parameter?
For ideal cubic perovskites:
a = SQRT(2)(rA + rO) = 2(rB + rO)
rearrange these to get
(rA + rO) = a/(SQRT(2)
SQRT(2)(rB + rO) = a*SQRT(2)/2

Sub into your equation, and the tolerance factor should equal 1, expected value for ideal cubic perovskite  Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode 