Elastic behavior associated with phase transitions in incommensurateBa2NaNb5O15

Abstract

The elastic behavior of barium sodium niobate ͑Ba 2 NaNb 5 O 15 ͒ has been investigated by resonant ultrasound spectroscopy through six different structural phases, with emphasis on the five incommensurate phase transitions near 40, 110, 547, 565, and 582 K. Data near 40 K are at least consistent with the existence of a lock-in transition to P4nm at that temperature ͓Filipic et al., J. Phys.: Condens. Matter 19, 236206 ͑2007͔͒, which has been controversial. A relaxation process occurs around the transition near 110 K and is assigned to a process involving movement of domain walls of the phase. Unusual behavior is observed through the high-temperature incommensurate transitions with large variations in frequency in the ultrasonic resonances, and a broad peak in the dissipation. No clear signature of the 1q-2q incommensurate-incommensurate transition at 565 K is observed. This is compatible with a model in which incommensurate-incommensurate transitions are not expected to manifest elastic anomalies.

Phase diagram and phase transitions in ferroelectrictris-sarcosine calcium chloride and its brominated isomorphs

“…Note, in the top trace, that there is a small peak at 64 K and also one at 74 K; the 64-K transition is slightly first order, and this may be due to thermal hysteresis (other anomalies are also found at 74 K), alternatively, it could involve subsidiary dielectric anomalies due to domains. 26 This figure shows, rather remarkably, the fact that, for the brominated specimens (not pure TSCC), the dielectric peak at 64 K disappears for slow (K/min) cooling runs [as in Fig. 3(b)].…”

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5OSmith1, Gardner2, Morrison3 et al. 2018Phys. Rev. MaterialsSelf Cite3020View full textAdd to dashboardCite

“…It is possible that the differences in f 2 and Q -1 between cooling and heating in the temperature range ~50-295 K are due to opening up of grain boundaries associated with changes in volume due to structural changes below ~50 K. This effect has been seen, for example, when a polycrystalline sample of quartz with grain sizes in the range 0.1-0.3 mm is heated through the α β transition [74], except that opening of the grain boundaries causes the polycrystalline sample to become elastically softer rather than stiffer, as here. The broad peaks at ~270 K in the heating sequence and at ~240 K in the cooling sequence (Figure 7a), are reminiscent of broad peaks seen at ~200 K in RUS data collected from Ba2NaNb5O15 (BNN) [75] and an alternative explanation is that the loss is associated with pinning (during cooling) and unpinning (during heating) of ferroelastic twin walls in both materials. This would be analogous to the anelastic behaviour of twin walls in improper ferroelastic perovskites [76].…”

“…The broad peaks at ∼270 K in the heating sequence and at ∼240 K in the cooling sequence [ Fig. 7(a)] are reminiscent of broad peaks seen at ∼200 K in RUS data collected from Ba 2 NaNb 5 O 15 (BNN) [77] and an alternative explanation is that the loss is associated with pinning (during cooling) and unpinning (during heating) of ferroelastic twin walls in both materials. This would be analogous to the anelastic behavior of twin walls in improper ferroelastic perovskites [78].…”

Formation of Ba2NaNb5O15 Crystal and Crystallization Kinetics in BaO–Na2O–Nb2O5–SiO2–B2O3 Glass

“…The ferroelectric orthorhombic Pba2 structure BNN with the lattice parameters a = 12.425, b = 12.484, c = 3.997 Å at room temperature transforms to the ferroelectric tetragonal 4mm at 260 °C, and with further heating, to the paraelectric tetragonal 4/mmm at 560 °C. 4,5 At room temperature, BNN has the useful values of dielectric constant ε = 250 and spontaneous polarization P = 0.40 C/m 2 , 6 which can be compared with those of LiNbO 3 (ε = 80, P = 0.71 C/m 2 ), 7,8 LiTaO 3 (50, 0.5 C/m 2 ), 9 BaTiO 3 (3000, 0.25 C/m 2 ). 10 BNN has been used in second harmonic generation and electro-optic devices because of its high nonlinear coefficient and resistance to optical damage.…”

“…Barium sodium niobate (Ba 2 NaNb 5 O 15 , BNN) crystal has attracted attention for a long time because of its important physical properties of ferroelectricity, high nonlinear optical coefficient, and intense photoluminescence. − BNN crystal possesses a sequence of structural phase transitions accompanying the change of dielectric properties. The ferroelectric orthorhombic Pba 2 structure BNN with the lattice parameters a = 12.425, b = 12.484, c = 3.997 Å at room temperature transforms to the ferroelectric tetragonal 4mm at 260 °C, and with further heating, to the paraelectric tetragonal 4/ mmm at 560 °C. , At room temperature, BNN has the useful values of dielectric constant ε = 250 and spontaneous polarization P = 0.40 C/m 2 , which can be compared with those of LiNbO 3 (ε = 80, P = 0.71 C/m 2 ), , LiTaO 3 (50, 0.5 C/m 2 ), BaTiO 3 (3000, 0.25 C/m 2 ) . BNN has been used in second harmonic generation and electro-optic devices because of its high nonlinear coefficient and resistance to optical damage. , …”