Ceramic platelets and oriented single crystals of PbTiO3have been investigated by Raman and infrared spectroscopy. The symmetries of the zonehyphen;center optical phonons are described and their temperature dependences from 20ndash;760deg;K are studied, demonstrating that the doubly degenerate modes are relatively the ldquo;softest.rdquo; It is shown that their behavior accounts for the variation of the static dielectric constant in the ceramic between those temperatures if singly and doubly degenerate modes coexist as pairs of a twohyphen;mode type of behavior. It is found that the shorthyphen;range crystal anisotropy predominates over the longhyphen;range electrostatic force in determining phonon frequencies. Above the 760deg;K Curie temperature the Raman spectrum is entirely second order and quite indistinct. No lowhyphen;temperature phase transition is found.
展开▼
