Crystallographic Orientation Relationships Between SrTiO₃ and Ruddlesden‐Popper Phase

Abstract

The crystalline phase mixture and microstructure of SrO‐excess SrTiO3 powder sintered at 1350°C/4 h is analyzed using X‐ray diffractometry (XRD), and scanning and transmission electron microscopy (SEM and TEM). Second phases represented by Ruddlesden–Popper Sr3Ti2O7 (RP2) and Sr4Ti3O10 (RP3) coexist with SrTiO3 (ST), consistent with the SrO–TiO2 phase equilibrium diagram. Some ST grains contain inter‐grown RP2 lamellae that permits analysis of the ST‐RP2 interface. The ST‐RP2 boundary shared by (001)ST and (001)RP2, although containing a lattice mismatch, is accommodated by long‐range elastic strain. The crystallographic orientation relationships of ST and RP2 at the interface are determined by selected area diffraction patterns (SADP) and described by transformation matrices. The crystallographic shear structure across the ST–RP boundary exhibiting the characteristic α‐fringe pattern can be represented by a fault vector R = 1/2(111)ST.

Structure and microwave dielectric characteristics of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x ≤ 0.50) ceramics

“…However a very minor amount (1‐2 wt%) of Sr 3 Ti 2 O 7 (JCPD card 89‐1383) secondary phase was detected for the composition x ≥ 0.25 from the Rietveld analysis (see Figure .). In fact, a combination of R‐P phases can always be found in the end member (SrTiO 3 ) having excess SrO layers, and the real reason for the appearance of Sr 3 Ti 2 O 7 R‐P phase can be well explained by the reaction energies. Since the difference between the reaction energies of these R‐P phases such as Sr 2 TiO 4 ( n = 1) and Sr 3 Ti 2 O 7 ( n = 2) is very small, and it subsequently leads to the coexistence of different metastable phases in the sintered ceramics.…”

“…As the Q-factor holds inverse relationship with frequency (f) in microwave range, the product of Qf was used instead of Q, to evaluate the dielectric loss. In fact, a combination of R-P phases can always be found in the end member (SrTiO 3 ) having excess SrO layers, 18,19 (…”