Dielectric Properties and Phase Diagram of (Sr 1-x Ba x ) 2 Nb 2 O 7 Single Crystals.

Dielectric constants, εb′ and εc′ along the crystallographicbandcaxes respectively, were measured in a temperature range of 10 − 700 K on Ba-substituted Sr2Nb2O7single crystals with different Ba concentrations up tox= 0.32. Whenx= 0, two dielectric anomalies were observed atTI= 489 K and atTL= 100 K, owing to the incommensurate phase transition and the low-temperature ferroelectric phase transition, respectively. BothTIandTLdecrease with Ba-contentxat initial slopes of ca. −19 and −37 K/mol%, respectively, and become broad atx= 0.04 and almost disappear atx= 0.08. Furthermore, Ba-substitution induces a weak and broad dielectric maximum in εb' vs.Tcurve at approximatelyTm= 465 K forx> 0.2. Phase diagram of this system was proposed. [ABSTRACT FROM AUTHOR]