Barium hydroxide (Ba(OH)2.8H2O) (>

Barium hydroxide (Ba(OH)2.8H2O) (> %98, Acros Organics, CAS#: 12230-71-6) was used as barium source. The pressed pellets were first subjected to pre-infiltration by wetting the sides of the green-body with a prepared solution of barium hydroxide, followed by placement of the sample into the Teflon liner containing vessel (Parr Instruments 4748 model, USA), addition of the reaction solution, hydrothermal processing at 180 °C and 240 °C up to 72 h, washing by DI water and drying. The obtained samples were coded as BT1 for the sample formed at 240 °C for 24 h, and BT2 for the one obtained at 240 °C for 72 h. Similarly the samples produced at 180 °C for 24 h and 72 h were coded as BT3 and BT4, respectively.