Figure 1: Electrical resistance as a function of temperature and pressure for Ba0.61K0.39Mn2Bi2.

(a) and (b) Temperature dependent resistance of Ba0.61K0.39Mn2Bi2 at different pressures. (c) Pressure dependence of resistance measured at different temperatures, displaying a dome-like feature centered at ~20–23 GPa. (d) and (e) Blown-up R-T curves at different pressures, showing no evidence of superconductivity.

BaMn2Bi2 possesses an iso-structure of iron pnictide superconductors and similar antiferromagnetic (AFM) ground state to that of cuprates, therefore, it receives much more attention on its properties and is expected to be the parent compound of a new family of superconductors. When doped with potassium (K), BaMn2Bi2 undergoes a transition from an AFM insulator to an AFM metal. Consequently, it is of great interest to suppress the AFM order in the K-doped BaMn2Bi2 with the aim of exploring the potential superconductivity.

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Contributors: Dachun Gu, Xia Dai, Congcong Le, Liling Sun, Qi Wu, Bayrammurad Saparov, Jing Guo, Peiwen Gao,Shan Zhang, Yazhou Zhou, Chao Zhang, Shifeng Jin, Lun Xiong, Rui Li, Yanchun Li, Xiaodong Li, Jing Liu, Athena S Sefat, Jiangping Hu, Zhongxian Zhao

Lattice distortions corresponding to Ba displacements with respect to the FeAs sublattice are revealed to break the room-temperature tetragonal symmetry in Ba(Fe1−xCox)2As2. The displacements yield twin domains of the size of ≈10 nm. The domain size correlates with the magnitude of the local Fe magnetic moment and its non-monotonic dependence on Co concentration.

Lattice distortions corresponding to Ba displacements with respect to the FeAs sublattice are revealed to break the room-temperature tetragonal symmetry in Ba(Fe1-x Cox)2 As2. The displacements yield twin domains of the size of ≈10 nm. The domain size correlates with the magnitude of the local Fe magnetic moment and its non-monotonic dependence on Co concentration.

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Contributors: Claudia Cantoni, Michael A McGuire, Bayrammurad Saparov, Andrew F May, Trevor Keiber, Frank Bridges, Athena S Sefat, Brian C Sales

Figure 1

Temperature dependence of (a) resistivity, (b) magnetization and (c) heat capacity for the three samples of CaFe2As2.

The interplay between magnetism and crystal structures in three CaFe2As2 samples is studied. For the nonmagnetic quenched crystals, different crystalline domains with varying lattice parameters are found, and three phases (orthorhombic, tetragonal, and collapsed tetragonal) coexist between TS = 95 K and 45 K. Annealing of the quenched crystals at 350°C leads to a strain relief through a large (~1.3%) expansion of the c-parameter and a small (~0.2%) contraction of the a-parameter, and to local ~0.2 Å displacements at the atomic-level. This annealing procedure results in the most homogeneous crystals for which the antiferromagnetic and orthorhombic phase transitions occur at TN/TS = 168(1) K. In the 700°C-annealed crystal, an intermediate strain regime takes place, with tetragonal and orthorhombic structural phases coexisting between 80 to 120 K. The origin of such strong shifts in the transition temperatures are tied to structural parameters. Importantly, with annealing, an increase in the Fe-As length leads to more localized Fe electrons and higher local magnetic moments on Fe ions. Synergistic contribution of other structural parameters, including a decrease in the Fe-Fe distance, and a dramatic increase of the c-parameter, which enhances the Fermi surface nesting in CaFe2As2, are also discussed.

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Contributors: Bayrammurad Saparov, Claudia Cantoni, Minghu Pan, Thomas C. Hogan, William Ratcliff II, Stephen D. Wilson,Katharina Fritsch, Makoto Tachibana, Bruce D. Gaulin, and Athena S. Sefat

PHOTOVOLTAIC PROPERTIES OF TWO-DIMENSIONAL (CH3NH3)2PB(SCN)2I2 PEROVSKITE: A COMBINED EXPERIMENTAL AND DENSITY FUNCTIONAL THEORY STUDY.

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We explore the photovoltaic-relevant properties of the 2D MA2Pb(SCN)2I2 (where MA = CH3NH3(+)) perovskite using a combination of materials synthesis, characterization and density functional theory calculation, and determine electronic properties of MA2Pb(SCN)2I2 that are significantly different from those previously reported in literature. The layered perovskite with mixed-anions exhibits an indirect bandgap of ∼2.04 eV, with a slightly larger direct bandgap of ∼2.

Contributors: Zewen Xiao, Weiwei Meng, Bayrammurad Saparov, Hsin-Sheng Duan, Changlei Wang, Chunbao Feng, Weiqiang Liao, Weijun Ke, Dewei Zhao, Jianbo Wang, David B Mitzi, Yanfa Yan

Although known since the late 19th century,

organic-inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic-inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

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Contributors:

Bayrammurad Saparov, David B Mitzi

Lead thiocyanate in the perovskite precursor can increase the grain size of a perovskite thin film and reduce the conductivity of the grain boundaries, leading to perovskite solar cells with reduced hysteresis and enhanced fill factor. A planar perovskite solar cell with grain boundary and interface passivation achieves a steady-state efficiency of 18.42%.

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Contributors:

Weijun Ke, Chuanxiao Xiao, Changlei Wang, Bayrammurad Saparov, Hsin-Sheng Duan, Dewei Zhao,Zewen Xiao, Philip Schulz, Steven P Harvey, Weiqiang Liao, Weiwei Meng, Yue Yu, Alexander J Cimaroli, Chun-Sheng Jiang, Kai Zhu, Mowafak Al-Jassim, Guojia Fang, David B Mitzi, Yanfa Yan