Lanthanide-Containing Zirconotitanate Solid Solutions

Shoup, Shara S.; Bamberger, C.E.; Tyree, Jennifer L.; Anovitz, Lawrence M.

doi:10.1006/jssc.1996.0379

Cited by 26 publications

(12 citation statements)

References 6 publications

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“…Two phases coexist in the titanate matrix: the major compound with a monoclinic symmetry of the framework and the minor portion of pyrochlore. This provides evidence for a narrower compositional area of the monoclinic phase, which is consistent with the results of investigation of the phase structure of the Nd 2 O 3 -TiO 2 -ZrO 2 system [14]. We established the low stability of the titanate monoclinic phase to radia tion; the dose of its amorphization is on the level of values for La 2 Ti 2 O 7 of the same structure and titanate pyrochlores.…”

Section: Phase Composition and Radiation Stability Of Matrices For Issupporting

confidence: 83%

Phase composition and radiation stability of matrices for isolation of REE-actinide waste

Лаверов

Yudintsev

Stefanovsky³

et al. 2012

Dokl. Earth Sc.

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526Safe treatment with highly radioactive wastes from processing of irradiated fuel is a key problem at the final stage of the nuclear energy cycle. The waste prod ucts are currently immobilized in glassy matrices for loading in underground storage [1]. Glasses are insuf ficiently stable for isolation of long living radionu clides, including actinides. It is suggested to fraction ate such wastes and include long living nuclides in the most stable crystalline matrices in order to increase safety [2]. The available technologies allow us to sepa rate actinides (U, Np, Pu), the REE-actinide compo nent, and products of decay.Zirconates and titanates with the structures of pyrochlore, zirconolite, perovskite, murataite, and others are suggested for isolation of actinide wastes [1-10 and others]. Materials with wastes of simple composition (plutonium and its imitators) were basi cally studied in these investigations; less attention was given to matrices for immobilization of the REEactinide fraction. Its approximate composition is the following (wt %): 80-90 REE + 10-20 actinides, where light lanthanides (La, Ce, Pr, Nd, and Sm) pre vail among REEs, and actinides are mainly repre sented by Am and Cm. The structure of matrices undergoes changes during actinide decay, which may influence their isolation properties.In this paper we report the new data on the struc tural peculiarities of perspective matrices for the REE actinide fraction and their radiation stability during irradiation by accelerated krypton ions.The starting charge was prepared from TiO 2 , ZrO 2 , and a mixture of REE oxides taken in proportions cor responding to the ideal formula (REE) 2 Zr 2 -x Ti x O 7 , where х = 0 (Sample Z) or 2 (Sample T). The propor tions of elements in the REE mixture are the following (wt %): La 4.7 (or in atomic proportions: 0.24La + 0.46Ce + 0.21Pr + 0.75Nd + 0.15Sm + 0.02Eu + 0.03Gd + 0.14Y); they reflect the proportions between them in the REEactinide fraction of wastes from reprocessing of irradi ated nuclear fuel. The size of the Nd 3+ cation is close to the sizes of the Am 3+ and Cm 3+ cations, that is why it was an imitator of these actinides. The mixtures were homogenized carefully and pressed into tablets at 200 atm and 25°С, and after that they were loaded in the oven for 5 h at 1550°С (х = 0) or 1400°С (х = 2). Reaching equilibrium in the zirconate system requires higher temperatures for acceleration of the phase for mation during synthesis. The samples were studied by X ray diffraction (XRD) and on a scanning electron microscope equipped with an energy dispersive spec trometer (SEM/EDS). They were irradiated in the Argonne National Laboratory (United States) on an accelerator combined with a transmission electron microscope [7]. This approach allows us to observe disordering of atoms in the framework and destruction upon irradiation. This method is an express way to determine the doses of amorphization in a wide tem perature range [1-3, 6-8, and others].According to the XRD data, Sample Z consists of dominating pyro...

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Section: Phase Composition and Radiation Stability Of Matrices For Issupporting

confidence: 83%

Phase composition and radiation stability of matrices for isolation of REE-actinide waste

Лаверов

Yudintsev

Stefanovsky³

et al. 2012

Dokl. Earth Sc.

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“…As to physical properties, Nd 2 Ti 2 O 7 is characterized by an extremely high Curie temperature T C > 1500°C, spontaneous polarization P s = 9 lC/cm 2 , high permittivity e = 31-47 [1,[3][4][5] and high piezoelectric properties [1,6] that holds promises for using this compound for the manufacture of ferroelectric random access memory (FRAM) elements [7][8][9][10][11]. Thermal stability up to T$1400°C and low dielectric losses open the way for a wide use of NTO as a key component in the fabrication of microwave ceramics and nanocomposites [12][13][14][15][16][17][18][19][20][21][22]. High refractive indices n a = 2.15, n b = 2.27 and n c = 2.23 (k = 526.5 nm) and a reasonable level of nonlinear optical susceptibility were measured for NTO [4,[23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of layered titanate Nd2Ti2O7

et al. 2008

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“…The pyrochlore field extends along the Nd 2 Zr 2 O 7 -Nd 2 Ti 2 O 7 line (Fig. 2) to the following values, mol %: 50 NdO 1.5 , 28.5 ZrO 2 , 21.5 TiO 2 [28], and the titanium-richest composition corresponds to the formula Nd 2 (Zr 1.14 Ti 0.86 )O 7 . Our results disagree with the data of Harvey et al [33], where higher Ti content of pyrochlore is reported, 56 mol % Nd 2 Ti 2 O 7 , which corresponds to the formula Nd 2 (Zr 0.89 Ti 1.11 )O 7 .…”

Section: Resultsmentioning

confidence: 96%

“…The atomic content of elements counting on Ti 4+ + Zr 4+ = 2 differs from the ideal formula in lower content of Nd 3+ and О 2-. The deficiency of ions is quite common for these positions in the pyrochlore structure, which is due to crystal-chemical features of compounds of this type [28][29][30].…”

Section: Resultsmentioning

confidence: 99%

Matrices for immobilization of the rare earth–actinide waste fraction, synthesized by cold crucible induction melting

et al. 2015

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The structure of eight samples containing simulated rare earth-actinide fraction of high-level waste was studied. Samples of weight from 0.2 to 6 kg were prepared by cold crucible induction melting followed by crystallization of the melt. The target phases (britholite, pyrochlore, zirconolite, rhombic and monoclinic rare earth titanates) prevail in all the matrices; glass, zirconolite, and rutile were detected as impurities, sometimes in significant amounts. These phases do not contain waste components (rutile) or are stable in solutions (zirconolite); therefore, their presence should not impair the properties of the matrix. The possibility of controlling the phase composition of the matrix by introducing zirconium or aluminum oxide into the charge was demonstrated.

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Lanthanide-Containing Zirconotitanate Solid Solutions

Cited by 26 publications

References 6 publications

Phase composition and radiation stability of matrices for isolation of REE-actinide waste

Phase composition and radiation stability of matrices for isolation of REE-actinide waste

Electronic structure of layered titanate Nd2Ti2O7

Matrices for immobilization of the rare earth–actinide waste fraction, synthesized by cold crucible induction melting

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