Guisheng Xu

GROWTH AND CHARACTERIZATION OF RELAXOR FERROELECTRIC PMNT SINGLE CRYSTALS

Abstract The results of relaxor ferroelectric PMNT single crystals grown by a modified Bridgman method with the size more than φ25×40 mm are reported in this paper. The crystal habit and growth mechanism of PMNT has been investigated to optimize the growth conditions. The reason that the PMNT crystals will grow along [111] direction under the condition of no seed crystals has been illustrated. It was found that the domain configuration in PMNT is much complicated and they will dominate the piezoelectric properties of PMNT single crystals. The characterization of PMNT single crystals shows that PMNT 67/33 single crystals have d33>2000pC/N. ϵ∼5500, k33-0.93.

GROWTH, CHARACTERIZATION AND PROPERTIES OF RELAXOR FERROELECTRIC PMN-PT SINGLE CRYSTALS

Abstract The present paper reviews the recent progress of studies on growth, characterization and properties of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals in Shanghai Institute of Ceramics. Their chemical compositions were selected near the rhombohedral-tetragonal morphotropic phase boundary, more favorable in the rhombohedral phase. The dominant method used for growing the single crystals was the modified Bridgman technique, by which the single crystal boules with the size larger than 25mm diameter and 50 mm long were grown. Different orientation thin plates with thickness less than 1mm were cut from the boules and their domain structures, morphology and properties were characterized. Their phase transition were discussed as well.

Growth and electrical properties of large size Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystals prepared by the vertical Bridgman technique

Relaxor-based ferroelectric single crystals Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIMNT) have been grown directly from their melt using the vertical Bridgman method, and their boules have reached the size of ϕ45×80mm. The as-grown PIMNT28/40/32 crystals on the (001) cuts exhibit a dielectric constant e∼5200, dielectric loss tanδ∼0.50%, piezoelectric strain constant d33∼1700–2200pC∕N, electromechanical coupling factors kt∼0.61 and k33∼0.92, coercive field Ec∼10.88kV∕cm, remanent polarization Pr∼46μC∕cm2, Curie temperature TC∼192°C, and rhombohedral to tetragonal phase transition temperature Trt∼119°C. Moreover, their piezoelectric properties show good thermal stability under the heat treatment at 105°C.

Growth and piezoelectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals by the modified Bridgman technique

Abstract The Bridgman technique has been used to grow PMNT single crystals based on the understanding of the features of PMN–PT system and the thermal stability of PMNT crystals. The technique has some advantages for the control of spontaneous nucleation, parasitic growth, crystal size and perfection compared to conventional methods. In order to suppress the leaking of crucibles, improve the compositional uniformity and enhance the piezoelectric performance, some modifications were adopted in starting materials and crystal growth procedure. The PMNT crystals grown using this technique were large in size and excellent in piezoelectric properties.

Dielectric and piezoelectric properties of lead-free 0.95(K0.5Na0.5)NbO3–0.05LiNbO3 crystals grown by the Bridgman method

Lead-free potassium sodium niobate piezoelectric single crystals substituted with lithium 0.95(K0.5Na0.5)NbO3–0.05LiNbO3 have been grown by Bridgman method and their dielectric and piezoelectric properties were studied. The orthorhombic-tetragonal and tetragonal-cubic phase transition temperatures of the single crystal appear at 192 and 426°C according to the dielectric constant versus temperature loops, respectively, and the (001) plates show good piezoelectric properties with piezoelectric constant d33 as high as 405pC∕N, large thickness electromechanical coupling factor kt=61%, and low dielectric constant of 185 at room temperature. These excellent properties show that the 0.95(K0.5Na0.5)NbO3–0.05LiNbO3 single crystal is a good lead-free piezoelectric material.

Ferroelectric and piezoelectric properties of novel relaxor ferroelectric single crystals PMNT

Relaxor ferroelectric single crystals PMNT with the size of ϕ40 mm × 80 mm have been grown by a modified Bridgman method and their ferroelectric and piezoelectric properties have been characterized. The properties varied with the compositions and cut types. On the (001) cut, PMNT76/24 single crystals exhibited a dielectric constant ∈ of about 3 400, a dielectric loss of tanδ <0.7%, a piezoelectric constantd33 of 980 pC/N, an electromechanical coupling factorkt of 0.55 andTc of about 110°C. Whereas the properties of PMNT67/33 single crystals on (001) cut were better:∈ of about 5 300, tanδ <0.6%, d33 up to 3 000 pC/N,kt 0.64, k33 0.93 and Tc of about 150°C. The piezoelectric properties on other cuts such as (110) and (111) were much lower than those on the (001) cut. The rhombohedral PMNT crystals grown by this method showed more excellent piezoelectric properties than those grown by high temperature solution method and higher value of kt than the rhombohedral PZNT single crystals. It has also been found that the fluctuation in ferroelectric and piezoelectric properties was related to such factors as composition uniformity and poling degree.

Structural defects of Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals grown by a Bridgman method

The types, formation mechanism and suppressing approaches of structural defects in PMNT crystals grown by a Bridgman method were investigated in this paper. The structural defects include composition non-uniformity, scattering particles, pores, negative crystal structures, cellular structures, fissure structures and point defects. They are formed due to one or several of the following: composition deviation, incomplete melting and diffusion, high-temperature volatilization, temperature fluctuation and instability of the position and shape of growth interfaces. On understanding the formation mechanism of structural defects, one can restrain them by means of adjusting stoichiometry of starting materials, using PMNT crystal bulks, suppressing composition volatilization and modifying growth parameters.

Growth and electrical properties of Pb(Sc1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary single crystals by a modified Bridgman technique

Single crystals of 0.05Pb(Sc 1.2 Nb 1.2 )O 3 -0.63Pb(Mg 1.3 Nb 2.3 )O 3 -0.32PbTiO 3 have been grown directly from melt by a modified Bridgman technique. The crystals with perovskite structure were 15 mm in diameter and 20 mm in length. The segregation during the growth of the single crystals was studied by means of X-ray diffraction analysis. The results show that PbTiO 3 content increases throughout the crystal growth. The electrical properties of the single crystals oriented along the [001] axis have been characterized. The plates cut from the seed end of a boule exhibited a permittivity (e 33 /e 0 ) of about 3500, dielectric loss tangent (tgδ)<1%, dielectric constant peaks at 162°C, piezoelectric constant (d 33 ) ≃ 1200 pC/N, and electromechanical coupling factor (k t ) ≃ 60% for the thickness mode. Our results show that xPb(Sc 1/2 Nb1 /2 )O3-yPb(Mg 1.3 Nb 2.3 )O 3 -(1-x-y)PbTiO 3 single crystals are promising for a wide range of electromechanical transducer applications.

Growth and Dielectric Properties of 0.48 Pb(Fe1/2Nb1/2)O3–0.52 PbTiO3 Single Crystal

Large ferroelectric single crystals of 0.48 Pb(Fe1/2Nb1/2)O3?0.52 PbTiO3 solid solution system were first successfully grown using a modified Bridgman technique and their properties were investigated. The obtained crystals were about 25 mm in diameter, 100 mm in length and black in color. The crystal exhibited abnormal dielectric properties that the dielectric constant was as high as 30000 and the dielectric loss factor was about 0.5 at room temperature. The mechanism of this phenomenon was discussed.

Ferroelectric phase transition in relaxor ferroelectric single crystals 0.76PMN-0.24PT

The features of the single crystals 0.76PMN-0.24PT in dietectric, ferroetectric, pyroetectric properties and domain structures indicate that they are located between typical ferroetectrics and normal ones. The unpoled crystals present a transitional domain configuration between microdomains and typical macrodomains while the crystals on (001) cuts undergo fietd-induced phase transition under poling, showing two special temperature points Td andTm during the succedent heating procedure. The dietectric constant starts to decrease drastically at Td during cooling, or the transformation from induced macrodomain to transitional domain takes place atTd during heating. Ferroetectric-paraetectric phase transition or depolarization continues within the whole temperature range ofTd-Tm, where ferroetectric phase in the form of transitional macrodomains coexists with paraetectric phase. Then the crystals macroscopically transoform into paraetectric phase containing ferroetectric microdomains at a temperature aboveTm. However, owing to the influence of crystallite orientation on fietd-induced phase transition, the temperatureTd does not appear in the same temperature-etectric fietd history in multicrystal ceramics with the same composition as the above single crystals.