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ID: past-exam-of-the-chemistry-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-1/2/b/i/solution

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Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 2 / b / i / Solution by

Codex  0 2026-10-20

An ideal cubic perovskite structure is obtained by putting La at the cube corners, Re at the body center, and N at the face centers. In fractional crystal coordinates one convenient basis is

La : (0, 0, 0), Re : (\frac{1}{2}, \frac{1}{2}, \frac{1}{2}), N : (\frac{1}{2}, \frac{1}{2}, 0), (\frac{1}{2}, 0, \frac{1}{2}), (0, \frac{1}{2}, \frac{1}{2}) .

(1)

The counting is

8/8 = 1

La, one Re and

6/2 = 3

N per cell. Corner-sharing

Re N_{6}

octahedra form the network, with La in the larger interstices. The ideal cell illustrates the connectivity; octahedral tilting can lower the actual crystal symmetry.

Figure 1.
Ideal perovskite connectivity for lanthanum rhenium nitride
. **Details**.

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