Phase Transition Domains in Ca‐based Complex Perovskite Dielectric Ceramics

Abstract

Phase transition‐induced lamellar domain structures together with the phase transition process in Ca [( Mg 1/3 Ta 2/3)0.9 Ti 0.1] O 3 complex perovskite ceramics have been investigated by high‐resolution transmission electron microscopy. As the orthorhombic and monoclinic structures coexist in the present ceramics and even in a single grain, groups of lamellar domains have been observed and analyzed in the three characteristic zone axes of the parent cubic perovskite structure: 〈100〉, 〈110〉, and 〈111〉. zone axes. The antiparallel displacement of A‐site cations, in‐phase, and antiphase oxygen octahedra tilting and B‐site 1:2 cation ordering cause superstructure reflections to destroy the symmetry of the parent cubic structure and subsequently induce domain structures. Groups of (010), (100) reflection twin domains and 90° rotation domains along the [100], [010], and [001] directions in the 〈100〉 and 〈110〉 zone axes are refined to be caused by the loss of reflection planes and fourfold rotation symmetry, whereas the loss of threefold rotoinversion and gain of twofold rotation symmetry lead to 120° and 180° rotation domains in the [111] zone axis. Rhombohedral 3 ¯ m and tetragonal 4/mmm structures are revealed to act as the bridging intermediate phase to make the first‐order phase transitions from the parent cubic m 3 ¯ m structure to the orthorhombic mmm structure and monoclinic 2/m structure without group‐subgroup relations continuous and diffusionless, and thus could occur via second order to form domain structures.

Structure and microwave dielectric properties of SrSmAlO4-Sr2TiO4 solid solutions

“…Recently, SrRAlO 4 (R=La, Nd, Sm) ceramics with K 2 NiF 4 layered structure and I4/mmm space group have been put forward as candidates of ultra-low loss microwave dielectric materials for high-band microwave application [3,4]. Compared with the typical high-Q microwave dielectric ceramics such as Ba(Mg 1/3 Ta 2/3 )O 3 [5], Ba(Zn 1/3 Ta 2/3 )O 3 [6], and Ba(Zn 1/3 Nb 2/3 )O 3 [7], SrRAlO 4 without noble elements such as Ta and Nb have the merits of relative low cost combined with its easier preparation. SrRAlO 4 (R=La, Nd, Sm) layered structure is composed by one perovskite layer (AlO 2 ) alternating with two rock salt layer ((Sr,R)O) and they can be viewed as two kinds of c h a r g e d l a y e r s : − A l O 2 -( S r , R ) O -( S r , R ) OAlO 2 -(Sr,R)O-(Sr,R)O-alternately stacking along the c-axis [8].…”

Effects of Y2O3 substitution on microwave dielectric properties of Ba(Co0.6Zn0.38)1/3Nb2/3O3 ceramics

“…They also found the appropriate content Zn deficiency on B 0 -site was beneficial for improving the microwave dielectric properties. Fu et al [23] studied the Ba(Zn 1-x Mg x ) 1/3 Nb 2/3 O 3 (x = 0-1) ceramics. From their results, Ba 5 Nb 4 O 15 was detected as the secondary phases due to the loss of zinc and cobalt during the sintering at high temperature.…”

“…In order to obtain relative high Q 9 f and adjust s f to zero, BCN and BZN have been modified using various valence states of different oxides, such as Al 2 O 3 [22], MgO [4,23], SnO 2 [24], SrO [25], WO 3 [24,26], ZrO 2 [1], Ta 2 O 5 [3], etc. Wu et al [26].…”

Improved high Q value of (1−x)Ca(Mg1/3Ta2/3)O3–xCa0.8Sm0.4/3TiO3 solid solution with zero temperature coefficient of resonant frequency

“…In addition, it possesses a high dielectric constant (ε r ∼ 21), a high quality factor (Q × f value ∼78,000 GHz) and a negative f value (−61 ppm/ • C) [13]. In order to compensate the f of the Ca(Mg 1/3 Ta 2/3 )O 3 , CaTiO 3 was added to form the 0.55Ca(Mg 1/3 Ta 2/3 )O 3 -0.45CaTiO 3 solid solution with an ε r ∼ 45.1, a Q × f value ∼34,800 GHz and a f value ∼17.4 ppm/ • C [14]. However, the Q × f still needs to be promoted before putting it to practical applications, such as GPS antennas.…”