When a block with a hole in it is heated why does not the material around the hole expand into the hole and make it small

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.

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What are the similarities & differences between a thermistor and a light dependent resistor in physics?