Ferroelectric crystal Ca9Yb(VO4)7 in the series of Ca9R(VO4)7 non-linear optical materials (R = REE, Bi, Y)статья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 8 сентября 2017 г.
Аннотация:The crystal structure, thermal, dielectric and second harmonic generation (SHG), and nonlinear optical
activity data for whitlockite-type Ca9Yb(VO4)7 single crystals were obtained on one and the same sample
produced by means of the Czochralski method. The crystal structure refinement has revealed that Yb3+
cations substitute for Ca2+ ions only in the M1, M2 and M5 positions of the whitlockite-type structure.
Dielectric, differential thermal analysis and SHG data have shown that Ca9Yb(VO4)7 belongs to the family
of high-temperature Ca3(VO4)2 ferroelectrics with Curie temperature Tc = 1221 K, where the symmetry
changes from R3c to R%3c. At higher temperatures a previously unknown complementary phase transition
is discovered at T2 = 1276 K and is associated with the symmetry change during heating from R%3c to
R%3m. Unlike other whitlockites, two phase transitions in Ca9Yb(VO4)7 are separated by a broad interval
(DT = 55 K) which allows one to register two phase transitions by DSC and dielectric measurements.
According to the thermal type both transitions are classified as first-order transformations and their
structural mechanisms are considered. Inhomogeneity in the cation distribution is argued to have a
crucial influence on the optical quality and ferroelectric domain structures of Ca9Yb(VO4)7 and other
whitlockite-type laser crystals.