This set of Ceramics Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Perovskite”.
1. What is the general formula of Perovskite?
a) ABO2
b) ABO3
c) ABO
d) ABO4
View Answer
Explanation: The ‘A’ cation and the anions effectively form an FCC array with a large octahedron in the center of the cell. Generally, the oxygen ions occupy face centers. Together ABO3 forms a stable structure.
2. What is the structure of CaTiO3 at room temperature?
a) Orthorhombic
b) Cubic
c) Monoclinic
d) Tetragonal
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Explanation: The mineral perovskite CaTiO3 has a orthorhombic structure at room temperature which is a stable structure. At high temperatures, the distortion becomes inevitable but the most symmetrically distorted structure is cubic. So it prefers to attain cubic structure.
3. Barium titanate has ideal perovskite structure above ________
a) 120°C
b) 220°C
c) 727°C
d) 432°C
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Explanation: Some amount of energy is required to place the ions on right position to form perovskite structure. This amount of energy is fulfilled a120°C of temperature. Therefore it has perovskite structure above 120°C.
4. Which of the following is a superconducting oxide?
a) YBCO
b) CaCO3
c) BaTiO3
d) MgSiO3
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Explanation: Yttrium barium copper oxide is a superconducting oxide. It shows superconductivity at 92K. CaCO3, BaTiO3, MgSiO3 are perovskites.
5. In BaTiO3 crystal structure, which position does the titanium cation occupy?
a) Center of the lattice
b) Face center
c) Body center
d) Corners
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Explanation: Titanium cation has four valence electrons. These four valence electrons can be satisfied only if it is placed at body center position. Hence it occupies center position of the lattice.
6. In BaTiO3 crystal structure, which position do oxygen anions occupy?
a) Center of the lattice
b) Face center
c) Body center
d) Corners
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Explanation: Oxygen anion has 2 valence electrons. These 2 valence electrons can be satisfied only if it is placed at face centers so that it can form 2 bonds. Hence it occupies face center position of the lattice.
7. What causes ferroelectricity in a perovskite?
a) Shifting off titanium cations from ideal position
b) Presence of defects and impurity
c) Brittleness
d) Presence of free electrons
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Explanation: The shifting off titanium cations from ideal position creates an electric dipole which polarizes the structure electrically. The structure becomes non-cubic. This causes ferroelectricity.
8. In the crystal structure of calcite, which position do calcium cations occupy?
a) Tetrahedral site
b) Face centers
c) Body centers
d) Octahedral sites
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Explanation: Calcium cation has 2 valence electrons. These 2 valence electrons can be satisfied only if it is placed at body centers so that it can form 2 bonds. Hence it occupies body center position of the lattice.
9. What is the melting point of barium titanate?
a) 1625°C
b) 1000°C
c) 850°C
d) 2564°C
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Explanation: It takes a lot of energy to break the ionic-covalent bonds of a ceramic perovskite structure. Thus melting point of barium titanate is 1625°C.
10. Why are perovskite crystal structure used in photocatalytic splitting of water?
a) Due to their diamagnetic nature
b) Due to their ferroelectric nature
c) Due to high dielectric constant
d) Due to their piezoelectric behaviour
View Answer
Explanation: Due to their piezoelectric behavior, they can trap ultra-violet rays and are able to split water into constituent molecules. Therefore they are used as photocatalytic splitting of water and in solar cells.
Sanfoundry Global Education & Learning Series – Ceramics Engineering.
To practice all areas of Ceramics Engineering, here is complete set of Multiple Choice Questions and Answers.
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