Electrical and transparent properties induced by structural modulation in (Sr0.925Ca0.075)2.5–0.5Na Nb5O15 ceramics

Abstract

The effects of Na + concentration on the microstructural, dielectric, ferroelectric and transparent properties of (Sr 0.925 Ca 0.075) 2.5−0.5x Na x Nb 5 O 15 (SCNN; 0.4 ≤ x ≤ 1.0) ceramics prepared using a conventional solid-state reaction method were investigated. X-ray diffraction results showed that the phase structure transitioned from tetragonal to orthorhombic tungsten bronze along with the structural type changing from 'unfilled' to 'filled' state. The NbO 6 octahedron became more distorted and had higher interaction strength when introducing Na + in A-sites to decrease the structural vacancies, leading to the improvement of dielectric and ferroelectric properties. The dielectric spectra of all specimens showed two broad dielectric anomalies: a hightemperature anomaly (the ferroelectric phase transition) and a low-temperature anomaly caused by the subtle structural effects in 'unfilled' SCNN ceramics, which evolved into the ferroelastic phase transition in 'filled' SCNN ceramics.

Relaxor Nature and Energy Storage Properties of Sr2–xMxNaNb5–xTixO15 (M = La3+ and Ho3+) Tungsten Bronze Ceramics

“…Parts a and b of Figure S4 show the Raman spectra of LT and HT ceramics in the frequency range from 130 to 1000 cm –1 , respectively. In the high-frequency range (>200 cm –1 ), it is easy to determine the three typical internal vibration modes in TTB, where ν 1 and ν 2 are classified as B–O stretching, and ν 5 is identified as O–B–O bending . In addition, the modes in the low frequency range are defined as external vibrations, which represent the displacement of cations relative to the oxygen octahedron.…”

“…In the high-frequency range (>200 cm −1 ), it is easy to determine the three typical internal vibration modes in TTB, where ν 1 and ν 2 are classified as B−O stretching, and ν 5 is identified as O−B−O bending. 43 In addition, the modes in the low frequency range are defined as external vibrations, which represent the displacement of cations relative to the oxygen octahedron. The ν 1 and ν 5 modes are observed to be slightly red-shifted in both LT and HT as the doping amount increases, indicating the expansion of the oxygen octahedron as the lattice constants decrease and the weakening of the B−O interaction caused by Ti 4+ replacing Nb 5+ .…”