Microwave Dielectric Properties of Perovskite-Like Structured Ba₈Ta₆(Ni_1-xM_x)O₂₄ (M=Co, Cu, and Zn) Solid Solutions

Abstract

Magnetic separatrix configurations have been produced in JET for plasma currents of up to 3 MA. Experimental results obtained with these configurations show that some features can be achieved that are common to divertor tokamaks. In Ohmic discharges, high recycling regimes can be produced. In neutral beam heated discharges, substantial improvement of the energy confinement time is achieved together with the characteristic signatures of an H-mode. These characteristics include improved particle confinement, flatter density profile, and an increase in electron temperature especially at the edge, leading to a characteristic pedestal feature. At higher neutral beam power, higher plasma densities are reached, with deterioration of beam penetration and strong radiation losses in the outer region of the plasma. The global energy confinement time in the H-mode is observed to degrade with additional power. However, results of radial power balance analysis suggest that in the central region, where the radiation is not important, the degradation of confinement is small.

New eight‐layer twinned hexagonal perovskite microwave dielectric ceramic Ba8NiNb6O24

“…Among the various hexagonal perovskite dielectrics, eight‐layer B‐site‐deficient hexagonal perovskites are the most fascinating compounds owing to (i) their high Qf values comparable to the values of complex tantalate perovskites compositions and (ii) the interesting twin‐shift phase competition and cationic ordering. Ba 8 M Ta 6 O 24 ( M= Zn, Ni, Co) adopts a eight‐layer twinned structure with a ( ccch ) 2 stacking sequence for BaO 3 layers and the B‐site vacancies and M 2+ cations are distributed in a partially ordered manner within the face‐sharing octahedral (FSO) dimers. These materials exhibit ε ~ 29, high Qf values ~70 000‐90 000 GHz, although the relatively high τ f values within ~30‐45 ppm/°C .…”

“…Ba 8 M Ta 6 O 24 ( M= Zn, Ni, Co) adopts a eight‐layer twinned structure with a ( ccch ) 2 stacking sequence for BaO 3 layers and the B‐site vacancies and M 2+ cations are distributed in a partially ordered manner within the face‐sharing octahedral (FSO) dimers. These materials exhibit ε ~ 29, high Qf values ~70 000‐90 000 GHz, although the relatively high τ f values within ~30‐45 ppm/°C . The search for cheaper niobate counterparts of the Ba 8 M Ta 6 O 24 led to the discovery of the eight‐layer shifted Ba 8 CoNb 6 O 24 and Ba 8 ZnNb 6 O 24 compounds.…”

The synthesis and polymorphic phase transitions of Ba4Nb2O9 ceramics

“…[1][2][3][4][5][6][7][8][9][10][11][12] In contrast to the archetypical cubic perovskites, the crystal structure of the hexagonal perovskites comprise face-sharing BX 6 octahedra along close-packed AX 3 layers comprising the (1 1 1) planes of the perovskite lattice. The layers of face-sharing octahedra break the usual ccp stacking along the <1 1 1> axes, the structure locally acquires the hcp stacking, and the axis normal to this layer becomes the c-axis of the hexagonal structure 13 .…”

Tuning the temperature coefficient of resonant frequency for 8-layer twinned hexagonal perovskite Ba8ZnTa6O24 ceramics

“…For example, 2:1-ordered Ba 3 ZnTa 2 O 9 and Ba 3 MgTa 2 O 9 ceramics have superior Q9f * 100,000-150,000 GHz, being able to offer efficient utilization of the allocated electromagnetic frequency window [3,4]. Recently, the closely related 8-layer twinned hexagonal perovskite tantalates [7][8][9][10][11][12] were reported to demonstrate good microwave dielectric properties, e.g. Ba 8 Li 2 Ta 6 O 24 [7] and Ba 8 MTa 6 O 24 (M = Zn, Ni, Co, Mg) [8][9][10][11] exhibit modest e r * 27-30, high Q9f * 70,000-100,000 GHz, comparable to the 2:1-ordered complex perovskite resonators.…”

“…Recently, the closely related 8-layer twinned hexagonal perovskite tantalates [7][8][9][10][11][12] were reported to demonstrate good microwave dielectric properties, e.g. Ba 8 Li 2 Ta 6 O 24 [7] and Ba 8 MTa 6 O 24 (M = Zn, Ni, Co, Mg) [8][9][10][11] exhibit modest e r * 27-30, high Q9f * 70,000-100,000 GHz, comparable to the 2:1-ordered complex perovskite resonators. Dense pellets of these hexagonal perovskite dielectrics can be obtained at temperatures significantly lower than the complex perovskites and do not require prolonged annealing to achieve cationic ordering for the high Q.…”