The heat capacity of ammonium chloride near the order-disorder transition
Schwartz, Paul Michael
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https://hdl.handle.net/2142/25796
Description
Title
The heat capacity of ammonium chloride near the order-disorder transition
Author(s)
Schwartz, Paul Michael
Issue Date
1969
Doctoral Committee Chair(s)
Slichter, C.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
heat capacity
ammonium chloride
order-disorder transition
first order phase transition
Language
en
Abstract
A theory is presented to explain the behavior of ammonium
chloride near the first order phase transition at 240K in terms of·
a physical model that has singular and nonsingu1ar parts of the free
energy coupled together. The singularity is normally associated with
a second order phase transition, but it can lead to a first order
transition in the model discussed.
The heat capacity at constant pressure is measured in the
neighborhood of the transition in order to test the predictiors of
the theory.
An A.C. technique is used to measure the heat capacity of
ammonium chloride single crystals, and a discussion of the
experimental factors involved in making the measurement is given. The
heat capacities measured showed a strong sample dependence.
Values are obtained for parameters occurring in the theory and are
compared with those obtained from other experiments on ammonium chloride
and from theoretical predictions. In particular, the volume dependence
of the interaction responsible for the transition is in qualitative
agreement with a prediction based upon an octopo1e-octopo1e,
electrostatic interaction. The critical exponents a+ and a are
found to be in the neighborhood of .7, which is quite different from.
the predictions of Ising model calculations.
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