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Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion (α) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, Cv.

In the Debye model, Cv is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus: $$\alpha \propto C_v$$ $$C_v \propto \frac {1}{c_s}$$ $$c_s \propto \sqrt{Y}$$ And therefore $$\alpha \propto \frac{1}{\sqrt{Y}}$$ Where Cs is the speed of sound in the solid and Y is Young's modulus.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Perhaps if you could share more about what contradictory information you've read, that might be helpful.

Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion ($\alpha$) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, $C_v$.

In the Debye model, $C_v$ is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus: $$\alpha \propto C_v$$ $$C_v \propto \frac {1}{c_s}$$ $$c_s \propto \sqrt{Y}$$ And therefore $$\alpha \propto \frac{1}{\sqrt{Y}}$$ Where $c_s$ is the speed of sound in the solid and Y is Young's modulus.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Perhaps if you could share more about what contradictory information you've read, that might be helpful.

Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion (α) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, Cv.

In the Debye model, Cv is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus: $$\alpha \propto C_v$$ $$C_v \propto \frac {1}{c_s}$$ $$c_s \propto \sqrt{Y}$$ And therefore $$\alpha \propto \frac{1}{\sqrt{Y}}$$ Where Cs is the speed of sound in the solid and Y is Young's modulus.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Perhaps if you could share more about what contradictory information you've read, it might be helpful.

Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion (α) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, Cv.

In the Debye model, Cv is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus: $$\alpha \propto C_v$$ $$C_v \propto \frac {1}{c_s}$$ $$c_s \propto \sqrt{Y}$$ And therefore $$\alpha \propto \frac{1}{\sqrt{Y}}$$ Where Cs is the speed of sound in the solid and Y is Young's modulus.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Perhaps if you could share more about what contradictory information you've read, that might be helpful.

Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion (α) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, Cv.

In the Debye model, Cv is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Thus your question, which seems to be why some ionic crystals have relatively high α's, would likely just mean that in this instance you cannot make an all encompassing general statement about α that is met by every such crystal.

Looking at Ziman's Principles of the Theory of Solids, section 2.10 he tells us that a first principles calculation of the coefficient of thermal expansion (α) is difficult, so he gives a phenomenological one the end result of which is that α is proportional to the specific heat at constant volume, Cv.

In the Debye model, Cv is inversely proportional to the speed of sound in a solid. Taking this one more step, the speed of sound in a solid is proportional to the Young's modulus of the solid, which is related to the bond strength.

Thus: $$\alpha \propto C_v$$ $$C_v \propto \frac {1}{c_s}$$ $$c_s \propto \sqrt{Y}$$ And therefore $$\alpha \propto \frac{1}{\sqrt{Y}}$$ Where Cs is the speed of sound in the solid and Y is Young's modulus.

Thus the coefficient of thermal expansion is approximately inversely proportional to the bond strength, which agrees with what you have been told. So that is correct.

Perhaps if you could share more about what contradictory information you've read, it might be helpful.