Study of tricritical point in triglycineselenate crystal by dynamical heat method at high pressure

The temperature dependences of the heat capacity of triglycineselenate crystal are experimentally studied over a broad range of temperatures and in direct proximity to the phase transition at different pressures up to 6.5 kbar. The dependences $(∆C)^{-2}=f(T)$ are approximated by straight lines only in the range $T_{c}$-T=0,2—1,5°С. The coefficient В in the Landau expansion of free energy is independent of pressure. Processing of the results in terms of critical indices showed there was a gradual variation in the index with pressure. At a pressure of 4 kbar, it was close to one half. The results are discussed under the assumption that defects influence the phase transition in triglycineselenate. It is concluded that at p = 1 bar, the phase transition in triglycineselenate is a phase transition of the first kind close to the tricritical point.