Xiqi Feng

Pyroelectric properties of [111]-oriented Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystals

The pyroelectric properties of [111]-oriented Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 (PMN-0.29PT) crystals have been investigated both as a function of frequency and temperature. At room temperature, [111]-oriented crystals have a high pyroelectric coefficient of 12.8×10−4C∕m2K and a low thermal diffusivity of ∼3.7×10−7m2∕s. The calculated voltage responsivity and detectivity figures of merit Fv and Fd exceed 0.11m2∕C and 9.8×10−5Pa−1∕2, respectively, over a wide range of frequency from 50 to 20000 kHz. The crystals are inert in practical application environment and can be easily processed as well. Such investigation reveals that superior pyroelectric performance makes PMN-0.29PT crystals a promising candidate for uncooled infrared detectors and imagers.

Pyroelectric performances of rhombohedral 0.42Pb(In 1/2 Nb 1/2 )O 3 -0.3Pb(Mg 1/3 Nb 2/3 )O 3 -0.28PbTiO 3 single crystals

Relaxor-based ferroelectric single crystals xPb(In_1/2Nb_1/2)O_3-yPb(Mg1/3Nb2/3)O3-(100x100y)PbTiO₃ {PIMNT [100x/100y/100(100x100y)]} have been grown by a modified Bridgman technique. The as-grown PIMNT (42/30/28) crystal with rhombohedral perovskite-type structure shows higher Curie temperature TC ~ 187°C, and higher ferroelectric rhombohedral-to-tetragonal phase transition temperature TRT ~ 152°C, both about 50°C higher than those found for 0.71Pb(Mg_1/3Nb_2/3)O₃-0.29PbTiO₃ crystals. Moreover, as a core parameter of pyroelectric material, the detectivity figures-of-merit of PIMNT (42/30/28) crystal are higher than other typical relaxor-based ferroelectric crystals, which primarily stems from the lower dielectric loss, making it promising candidate for infrared detector applications.

Ba3BP3O12:Eu2+—A potential scintillation material

The sample of Eu2+-doped Ba3BP3O12 was prepared by a solid-state reaction at high temperature and was showed to be an excellent scintillator when excited with hard x ray s. The phosphor showed a broad emission band in the wavelength range of 400–650 nm and a comparable light yield with that of Bi4Ge3O12 powders. Its room temperature fluorescence decay curve exhibited a two-exponent shape with decay time of 20.0±1.4ns (98.97%) and 522±9ns (1.03%), respectively. Considering the suitable emission wavelength range, large light yield, short decay time, moderate density, moderately low melting point, and nonhygroscopic property of Ba3BP3O12:Eu2+, one has reason to assume that this compound might find an application as a new scintillation material.

Crystal structure and magnetic properties of Pr5Si4−xGex compounds

The magnetic properties of Pr5Si4-xGex (x = 0.0, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0) were investigated by magnetic measurements. The compounds Pr5Si4-xGex crystallize in the tetragonal Zr5Si4-type structure for x = 0.0 and 1.0, in the monoclinic Gd5Si2Ge2-type structure for x = 2.0 and 2.5; and in the orthorhombic Sm5Ge4-type structure for x = 3.0-4.0. Unlike the heavy rare earth RE5Si4-xGex (RE = Gd, Tb, Dy) system, the Curie temperature of this system exhibits the following features: the Curie temperature of the compound increases with the increasing of the Ge content in the tetragonal phase region, whereas it shows a weak dependence on the Ge content in the monoclinic phase region and decreases in the orthorhombic phase region. All of the compounds in this system may have a canted magnetic structure

Structure dependence of magnetic properties of Nd5Si4−xGex (x=1.2 and 2)

The crystal structure and magnetic properties of ternary compounds Nd5Si4-xGex (x = 1.2 and 2) were investigated by means of X-ray powder diffraction and magnetic measurements. The as-cast samples alpha-Nd5Si2.8Ge1.2 and beta-Nd5Si2Ge2 crystallize in the orthorhombic Gd5Si4-type structure with space group Puma and the monoclinic Gd5Si2Ge2-type structure with space group P112(1)/a, respectively. The samples beta-Nd5Si2.8Ge1.2 and beta-Nd5Si2Ge2 annealed at 1273 K all crystallize in the tetragonal Zr5Si4-type structure with space group P4(1)2(1)2. All phases of alpha-Nd5Si2.8Ge1.2, beta-Nd5Si2.8Ge1.2, alpha-Nd5Si2Ge2 and beta-Nd5Si2Ge2 exhibit a spin glasslike behavior and may have a canted magnetic structure. The Curie temperature shows a strong dependence on the crystal structure of the compounds. The average interatomic distances of magnetic Nd atoms and the amount of the covalent (Si,Ge)-(Si,Ge) bond pairs in these phases are different, which may be responsible for their different magnetic properties

Magnetic phase transition and 3d susceptibility in Laves phase Gd1-xDyxCo2 compounds

Magnetization and AC susceptibility measurements have been carried out to investigate the magnetic phase transition of Gd1-xDYxCo2 compounds. It is revealed that the type of the magnetic phase transition changes from second order to first order around x(c) = 0.8 with the increase of Dy concentration. A satisfactory explanation is offered in terms of the Inoue-Shimizu model. The exchange-enhanced susceptibility of the compounds within the exchange-enhanced paramagnetism model is in good agreement with the 3d-electrons susceptibility deduced by Inoue-Shimizu model

Decoupling between rare-earth moment and transition metal moment in NdCo12-xVx compounds

Single-phase compounds NdCo12−xVxu200a(x=2.2–2.6) crystallizing in the tetragonal ThMn12 structure with space group I4/mmm are synthesized. The lattice parameters a and c increase linearly with increasing V content. The Curie temperature of the compounds shows a linear decrease from 309 K for x=2.2 to 147 K for x=2.6. A domain-wall pinning phenomenon is observed in all of the compounds. It is intriguing that the Nd ions seem to make no contribution to the total moment of the compounds in an applied magnetic field up to 50 kOe. A further increase of the applied field induces a moment of a Nd sublattice that ferromagnetically couples with the moment of a Co sublattice. The instability of the Nd moment in NdCo12−xVx compounds can be well understood by the local environment effect.