Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHigh oxygen pressure floating zone growth and crystal structure of the layered nickelates R$_4$Ni$_3$O$_{10}$ (R=La, Pr)
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Single crystals of the metallic Ruddlesden-Popper trilayer nickelates R$_4$Ni$_3$O$_{10}$ (R=La, Pr) were successfully grown using an optical-image floating zone furnace under oxygen pressure (pO$_2$) of 20 bar for La$_4$Ni$_3$O$_{10}$ and 140 bar for Pr$_4$Ni$_3$O$_{10}$. A combination of synchrotron and laboratory x-ray single crystal diffraction, high-resolution synchrotron x-ray powder diffraction and measurements of physical properties revealed that R$_4$Ni$_3$O$_{10}$ (R=La, Pr) crystallizes in the monoclinic $P$2$_1$/$a$ (Z=2) space group at room temperature, and that a metastable orthorhombic phase ($Bmab$) can be trapped by post-growth rapid cooling. Both La$_4$Ni$_3$O$_{10}$ and Pr$_4$Ni$_3$O$_{10}$ crystals undergo a metal-to-metal transition (MMT) below room temperature. In the case of Pr$_4$Ni$_3$O$_{10}$, the MMT is found at ~157.6 K. For La$_4$Ni$_3$O$_{10}$, the MMT depends on the lattice symmetry: 147.5 K for $Bmab$ vs. 138.6 K for $P$2$_1$/$a$. Lattice anomalies were found at the MMT that, when considered together with the pronounced dependence of the transition temperature on subtle structural differences between $Bmab$ and $P$2$_1$/$a$ phases, demonstrates a not insignificant coupling between electronic and lattice degrees of freedom in these trilayer nickelates.
rate research
Read More
We investigate the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, high-resolution synchrotron powder X-ray diffraction and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry, and undergo a metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At MMT, the lattice parameters show distinct anomalies; however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen in magnetic and thermal measurements, which suggest a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with experiments. We show that the 9-fold coordinated Pr ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering at 5 K. The Pr ions located in the perovskite block (PB) layers with 12-fold coordination, however, exhibit a non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like anomaly near35 K, and an upturn below T = 10 K suggesting the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy fermion behavior could be found in any of the three compounds.
Single crystals of PrNiO3 were grown under an oxygen pressure of 295 bar using a unique high-pressure optical-image floating zone furnace. The crystals, with volume in excess of 1 mm3, were characterized structurally using single crystal and powder X-ray diffraction. Resistivity, specific heat, and magnetic susceptibility were measured, all of which evidenced an abrupt, first order metal-insulator transition (MIT) at ~130 K, in agreement with previous literature reports on polycrystalline specimens. Temperature-dependent single crystal diffraction was performed to investigate changes through the MIT. Our study demonstrates the opportunity space for high fugacity, reactive environments for single crystal growth specifically of perovskite nickelates but more generally to correlated electron oxides.
High quality single crystals of BaFe$_{12}$O$_{19}$ were grown using the floating zone technique in flowing oxygen pressurized to 100 atm. Single crystal neutron diffraction was used to determine the nuclear and magnetic structure of BaFe$_{12}$O$_{19}$ at 4 K and 295 K. At both temperatures, there exist local electric dipoles formed by the off-mirror-plane displacements of magnetic Fe$^{3+}$ ions at the bipyramidal sites. The displacement at 4 K is about half of that at room temperature. The temperature dependence of the specific heat shows no anomaly associated with long range polar ordering in the temperature range from 1.90-300 K. The inverse dielectric permittivity, $1/varepsilon$, along the c-axis shows a $T^2$ temperature dependence between 10 K and 20 K, with a significantly reduced temperature dependence displayed below 10 K. Moreover, as the sample is cooled below 1.4 K there is an anomalous sharp upturn in $1/varepsilon$. These features resemble those of classic quantum paraelectrics such as SrTiO$_3$. The presence of the upturn in $1/varepsilon$ indicates that BaFe$_{12}$O$_{19}$ is a critical quantum paraelectric system with Fe$^{3+}$ ions involved in both magnetic and electric dipole formation.
Ab initio calculations have been performed to unravel the origin of the recently found superlattice peaks in the trilayer nickelate La$_4$Ni$_3$O$_8$. These peaks arise from static charge ordering of Ni$^{2+}$/ Ni$^{1+}$ stripes oriented at 45$^{circ}$ to the Ni-O bonds. An insulating state originates from a combination of structural distortions and magnetic order, with the gap being formed solely within the d$_{x^2-y^2}$ manifold of states. When doped, electrons or holes would go into these states, in a similar fashion to what occurs in the cuprates. Analogous calculations suggest that checkerboard charge order should occur in the bilayer nickelate La$_3$Ni$_2$O$_6$. These results reveal a close connection between La$_4$Ni$_3$O$_8$ and La$_3$Ni$_2$O$_6$ with La$_{2-x}$Sr$_x$NiO$_4$ for x=1/3 and x=1/2, respectively.
The wealth of structural phases seen in the rare-earth disilicate compounds promises an equally rich range of interesting magnetic properties. We report on the crystal growth by the optical floating zone method of members of the rare-earth disilicate family, $R_{2}$Si$_{2}$O$_{7}$ (with $R=$ Er, Ho, and Tm). Through a systematic study, we have optimised the growth conditions for Er$_{2}$Si$_{2}$O$_{7}$. We have grown, for the first time using the floating zone method, crystal boules of Ho$_{2}$Si$_{2}$O$_{7}$ and Tm$_{2}$Si$_{2}$O$_{7}$ compounds. We show that the difficulties encountered in the synthesis of polycrystalline and single crystal samples are due to the similar thermal stability ranges of different rare-earth silicate compounds in the temperature-composition phase diagrams of the $R$-Si-O systems. The addition of a small amount of SiO$_{2}$ excess allowed the amount of impurity phases present in the powder samples to be minimised. The phase composition analysis of the powder X-ray diffraction data collected on the as-grown boules revealed that they were of single phase, except in the case of thulium disilicate, which comprised of two phases. All growths resulted in multi-grain boules, from which sizable single crystals could be isolated. The optimum conditions used for the synthesis and crystal growth of polycrystalline and single crystal $R_{2}$Si$_{2}$O$_{7}$ materials are reported. Specific heat measurements of erbium and thulium disilicate compounds confirm an antiferromagnetic phase transition below $T_{mathrm{N}}=$ 1.8 K for D-type Er$_{2}$Si$_{2}$O$_{7}$ and a Schottky anomaly centered around 3.5 K in C-type Tm$_{2}$Si$_{2}$O$_{7}$, suggesting the onset of short-range magnetic correlations. Magnetic susceptibility data of E-type Ho$_{2}$Si$_{2}$O$_{7}$ reveals an antiferromagnetic ordering of the Ho spins below $T_mathrm{{N}}=$ 2.3 K.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
