A series of large-sized (maximum 16 × 16 × 20 mm 3 ), high-quality K 1−x Na x NbO 3 (x = 0.118, 0.378, 0.462, 0.545, and 0.666) single crystals were successfully cultivated using the top-seeded solution growth method. The crystallization and structures of the K 1−x Na x NbO 3 single crystals were studied using first-principles calculations and X-ray diffraction, respectively. The segregation of the K 1−x Na x NbO 3 single crystals was investigated, which enabled precise control of the individual components of the crystals during growth. Excellent properties were obtained without annealing, including a low dielectric loss (minimum 0.2%), a saturated hysteresis loop with a low coercive field E c , a large piezoelectric coefficient d 33 (d 33 = 161 pC/N when x = 0.378), and a low leakage current density J (10 −6 A/cm 2 ). These results indicated that the K 1−x Na x NbO 3 (x = 0.118, 0.378, 0.462, 0.545, and 0.666) crystals can be used as a high-quality, lead-free piezoelectric material.
Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K x Na 1−x )NbO 3 single crystals with an ultrahigh large-signal piezoelectric coefficient d 33 * of 9000 pm V −1 , which is superior to the highest value reported in stateof-the-art lead-based single crystals (~2500 pm V −1 ). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals. , Ultra-large electric field-induced strain in potassium sodium niobate crystals. Sci. Adv. 6, eaay5979 (2020).
The quadratic electro-optic effect in K0.95Na0.05Ta1−xNbxO3 crystals near the Curie temperature was investigated. Both the electro-optic coefficients |R11| and |R12| decreased rapidly as the temperature increased beyond the Curie point. Interestingly, the ratio |R11/R12| increased. The polar nanoregions found in K0.95Na0.05Ta1−xNbxO3 crystals near the Curie temperature are believed to be responsible for this effect. A phenomenological model is proposed to analyze the impact of these polar nanoregions on the quadratic electro-optic effect.
Internal
fields caused by strain gradient, composition gradient
(CG), and space charges have significant influences on micro and macro
properties of ferroelectrics. Here, we report the relationship among
composition gradient, microdomain structure, and macroscopic ferroelectric/piezoelectric
properties. Three KTa1–x
Nb
x
O3 samples with the same Curie
temperature T
c = 39 °C and different
CGs are designed and investigated. As CG decreases, the scale of domains
decreases from ∼10 μm to 200 nm, and the spontaneous
polarizations orientate more randomly, which leads to a smaller ratio
of lattice content c to a (c/a). Furthermore, dielectric constant
and d
33 increases dramatically from 6000
to 11 000 and from 203 to 345 pC N–1, respectively.
This relationship is important for prospective applications due to
its controllability of microdomains and polarization states. In addition,
we reveal that CG and composition fluctuation induce internal fields
(E
in) and resilience, respectively, leading
to the frequency-dependent biased and standard double polarization–electric
field (P–E) loops. Moreover,
the existence of CGs drives the formation of different size domains
by E
in, which provides a way to adjust
ferroelectric and piezoelectric properties by controlling CG. As well,
it is important for the study of flexoelectric on continuous CG bulk
materials.
Component regulation has a significant influence on the ferroelectric structural phase‐transition characteristics such as the temperature (Tc) and the functional properties. Here, the electrocaloric (EC) properties in potassium tantalate niobate (KTa1−xNbxO3) single crystal are reported. The KTN43 (x = 0.43) single crystal exhibits an adiabatic temperature change of ΔT = 0.76 K at 15 kV cm−1 with both the first‐order and the diffuse phase transition performances near Tc. It represents a good solution for the two intractable contradictions for electrocaloric effect (ECE), namely that the large EC peak value prevents a low working temperature and a wide temperature span. It is shown that improving the Nb component in KTN single crystal can obviously elevate the EC properties. KTN shows good EC properties, including large adiabatic temperature change, low driving electric fields, large refrigeration capacity, working near room temperature and reversibility for all temperature range. These properties indicate that KTN is a promising EC material for practical application.
The evolution of
domains, which reveals the special structure in
the vicinity of the para-ferroelectric phase transition, is the key
to explaining the excellent properties of ferroelectric materials.
However, although existing studies offer insight into the process
of the para-ferroelectric phase transition, questions remain regarding
the intermediate structure in the order–disorder state. To
investigate this phenomenon, we studied the stability and intensity
of polarization for the temperature-dependent microstructure, deduced
from the vibrations of ions. The evolution of polarization and orientation
in the polar regions is investigated through the vibrations of the
deformation of the octahedral units. In addition, the intensity and
full width at half-maximum (fwhm) of the B1+E(3TO) mode
revealed the stability of polar regions in the dynamic process, which
differentiates the static state and dynamic state. Such findings will
have a significant impact in the field of property manipulation.
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