Stabilizing the Tb-based 214 cuprate by partial Pd substitution
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Jing Tao Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, USA
Elizabeth M. Carnicom, Tai Kong, Marisa B. Sanders, and R. J. Cavab) Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA (Received 26 January 2018; accepted 3 April 2018)
Previously known to form only under high pressure synthetic conditions, here we report that the T9-type 214-structure cuprate based on the rare earth atom Tb is stabilized for ambient pressure synthesis through partial substitution of Pd for Cu. The new material is obtained in purest form for mixtures of nominal composition Tb1.96Cu0.8Pd0.2O4. The refined formula, in orthorhombic space group Pbca, with a 5 5.5117(1) Å, b 5 5.5088(1) Å, and c 5 11.8818(1) Å, is Tb2Cu0.83Pd0.17O4. An incommensurate structural modulation is seen along the a axis by electron diffraction and high resolution imaging. Magnetic susceptibility measurements reveal long-range antiferromagnetic ordering at 7.9 K, with a less pronounced feature at 95 K; a magnetic moment reorientation transition is observed to onset at a field of approximately 1.1 T at 3 K. The material is an n-type semiconductor.
I. INTRODUCTION
The R2CuO4 (“214”) rare earth (R) cuprates have been of interest due to their remarkable properties.1,2 Longrange magnetic ordering of the rare earth moments has been observed for a variety of these materials, including R 5 Gd, Tb, Dy, Ho, Er, and Tm.3–5 Most importantly, with the appropriate partial substitutions, R2CuO4 compounds with R 5 La, Pr, Nd, and Sm become n- or p-type high TC superconductors.6,7 R2CuO4 compounds based on the rare earths smaller than Gd have previously been synthesized only at high pressures, with at least 8 GPa applied pressure required to form 214 cuprates for R 5 Tb, Dy, Ho, and Er; no R2CuO4formula compounds are known to be stable at ambient pressure for the small rare earths.6,8,9 The materials display a rich evolution of structure based on the size of the rare earth ion. The structures range from the socalled T-type structure of La2CuO4, in which the Cu is in distorted octahedral coordination, through the T*-type structure typified by Nd2xzCexSrzCuO4 in which the Cu is in pyramidal coordination, through the T9 structure displayed by Nd2CuO4 in which the Cu is in square planar coordination. The T9-type 214 structure, which is of interest here, is most often reported as body-centered tetragonal, with Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2018.102
a0 ; 3.9 Å and c0 ; 11.0 Å, although there are reports of orthorhombic symmetry for T9-type Gd2CuO4 in a side-centered space group with a9 ; b9 ; O2 a0, and c9 ; c0.10,11 Three supercells have been reported for the T9 structure, with the most common (A) supercell having cell parameters of 2O2a0 O2a0 c0.9 The current study is based on the hypothesis that some of the rare-earth–based 214 cuprates previously formed only at high pressures might form at amb
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