H.Y-P. Hong

Fast Na+-ion transport in skeleton structures☆

Skeleton structures have been explored experimentally for fast Na+-ion transport. A skeleton structure consists of a rigid skeletal array of atoms stabilized by electrons donated by alkali ions partially occupying sites in a three dimensionally linked interstitial space. Fast Na+-ion transport was demonstrated in several structures, and the system Na1+xZr2P3−xSixO12 has a Na+-ion resistivity at 300°C of ϱ300 ≲ 5Ω-cm for x ≈ 2, which is competitive with the best β″-alumina. An activation energy ea ≈ 0.29 eV is about 0.1 eV larger than that of β″-alumina.

Crystal structures and crystal chemistry in the system Na1+xZr2SixP3−xO12☆

As part of a search for skeleton structures for fast alkali-ion transport, the system Na1+xZr2SixP3−xO12 has been prepared, analyzed structurally and ion exchanged reversibly with Li+, Ag+, and K+ ions. Single-crystal x-ray analysis was used to identify the composition NaZr2P3O12 and to refine its structure, which has rhombohedral space group R3c with cell parameters ar = 8.815(1)A and cr = 22.746(7)A. A small distortion to monoclinic symmetry occurs in the interval 1.8 ≤x≤ 2.2. The structure for Na3Zr2Si2PO12, proposed from powder data, has space group C2c with am = 15.586(9)A, bm = 9.029(4)A, cm = 9.205(5)A, and β = 123.70(5)° Both structures contain a rigid, three-dimensional network of PO4 or (SiO4) tetrahedra sharing corners with ZrO6 octahedra and a three-dimensionally linked interstitial space. Of the two distinguishable alkali-ion sites in the rhombohedral structure, one is completely occupied in both end members, the occupancy of the other varies across the system from 0 to 100 percent. Several properties are compared with the fast Na+-ion conductor β-alumina.

Crystal structure and ionic conductivity of Li14Zn(GeO4)4 and other new Li+ superionic conductors☆

Abstract This paper reports the synthesis and characterization of a number of new Li + superionic conductors with the type formula Li 16−2x D x (TO 4 ) 4 , where D is a divalent cation (Mg 2+ or Zn 2+ ), T is a tetravalent cation (Si 4+ or Ge 4+ ), and 0 14 Zn(GeO 4 ) 4 , has a resistivity of 8 ω-cm at 300°C, lower than that of any Li + -ion conductor so far reported. The structure of this compound, which we have named LISICON (for Li s uper io nic con ductor), has been determined by single-crystal x-ray analysis. The space group is Pnma, with cell parameters a =10.828 A , b =6.251 A , c =5.140 A , and z=1. The structure has a rigid three-dimensional network of Li 11 Zn(GeO 4 ) 4 . The three remaining Li + ions have occupancies of 55 and 16%, respectively, at the 4c and 4a interstitial positions. Each 4c position is connected to two 4a positions and vice versa. The bottlenecks betweenthese positions have an average diameter that is larger than twice the sum of the Li + and O 2− ionic radii, thus satisfying thegeometrical condition for fast Li + -ion transport. Moreover, all four sp 3 orbitals of the O 2− ion are shared by strong tetrahedral covalent bonds with the network cations. Therefore, the anion charge is polarized away from the interstitial Li + ions, weakening the Li1bO bond and increasing the Li + -ion mobility.

Crystal structure and fluorescence lifetime of NdAl3(BO3)4, a promising laser material☆

The structure of NdAl3(BO3)4, determined by single-crystal x-ray analysis, is rhombohedral with space group R32 and cell parameters a = 9.3416 (6)A, c = 7.3066 (8)A, Z = 3. A full-matrix, least-squares refinement gives R = 0.033 and Rw = 0.037. The Nd atoms, Al atoms and B atoms occupy trigonal prisms, octahedra, and triangles of oxygen, respectively. Edge-shared Al octahedra form helices along the c-axis. These helices are connected by isolated B triangles and isolated Nd trigonal prisms. The fluorescence lifetime of the 4F32 → 4I112 transition of Nd+3 is reported for the system NdxGd1−xAl3(BO3)4. The lifetime of NdAl3(BO3)4 is 19us, and concentration quenching is reduced in the series, as happens in NdNa5(WO4)4 (85μs) and NdP5O14 (115μs). The shorter lifetime is attributed to noncentrosymmetry; the reduced concentration quenching to isolation of Nd polyhedra.

Crystal structure of NdLiP4O12

Abstract A single-crystal x-ray diffraction analysis has been performed on NdLiP 4 O 12 synthesized by a flux method. The structure is monoclinic, with space group C 2/c, Z = 4, and cell parameters a = 16.408 (3), b = 7.035 (4), c = 9.729 (4) A , and β = 126.38 (5)°. A full-matrix, least squares refinement gave R = 0.072, Rw = 0.077 for 590 independent reflections. The basic structural units are helical ribbons, (PO 3 ) n , formed by corner-sharing of PO 4 tetrahedra. The NdO 8 dodecahedra are isolated from each other in the sense that they do not share any O atoms. This isolation accounts for the marked reduction in the concentration quenching of Nd +3 fluorescence that is observed for NdLiP 4 O 12 . The shortest Nd-Nd distance is 5.620 A, and the concentration of Nd +3 ions is 4.42 × 10 21 cm −3

High Na+-ion conductivity in Na5YSi4O12

Ceramic specimens of Na5YSi4O12 with densities up to 95% of theoretical and Na+-ion conductivities at 300°C up to 0.15 Ω−1 cm−1 have been fabricated from powders synthesized by solid-state reaction of Na2C2O4, Y2(C2O4)3, and SiO2. Conductivity values obtained by complex impedance measurements on one specimen between 25 and 320°C gave an activation energy of 0.15 eV above 175°C, but the ln (σ T) versus 1/T plot was not linear at the lower temperatures.

Crystal chemistry in the system MSbO3

Abstract Cubic, disordered phases of the compounds MSbO 3 (M = Li, Na, K, Rb, Tl, and Ag) have been investigated. KSbO 3 is readily synthesized in the disordered, cubic structure at high pressure, and the other isomorphic compounds were obtained by ion exchange. The structures of NaSbO 3 and AgSbO 3 , which have space group Im 3, were solved by X-ray single-crystal analysis. The structures contain an essentially rigid SbO 3 subarray consisting of pairs of edge-shared octahedra sharing common corners. Within this subarray, face-shared octahedra form 〈111〉 tunnels that intersect at the origin and body center of the unit cell, and the M + ions are randomly distributed over two positions within these tunnels. Ordered, cubic phases have the primitive-cubic space group Pn 3. The two M positions are different for Na + and for Ag + ions. At one of the Ag + -ion positions, the AgO bond length is only 2.26 A, consistent with the gray-black color of AgSbO 3 . Deformation of the 4 d 10 Ag + -ion core by 4 d -5 s hybridization appears to be induced by AgO covalent bonding. This conclusion is compatible with the observation that ion exchange is reversible for all compounds but AgSbO 3 . Several properties of these compounds are compared with the super ionic conductors M 2 O·11Al 2 O 3 β-alumina.

Crystal structure of Ytterbium ultraphosphate, YbP5O14☆

Abstract The structure of monoclinic YbP5O14, space group C2/c (No. 15), a = 12.830(3) A , b = 12.676(3) A , c = 12.337(3) A , β = 91.25(2)°, z = 8 , has been determined from single-crystal data. Isolation of the rare-earth sites gives a relatively long distance (5.686A) between near-neighbor Yb+3 ions. Comparison with the two other ultraphosphate structures shows that such long distances are an important characteristics of the data phosphate structures having long fluorescence lifetimes.

Crystal structure and fluorescence lifetime of a laser material NdNa5(WO4)4

Abstract The structure of NdNa 5 (WO 4 ) 4 , determined by single-crystal x-ray analysis, is tetragonal with space group I 4 1 /a and cell parameters a = 11.559(2) A , b = 11.453(2) A , z = 4. A full-matrix, least-squares refinement gives R = 0.077. The W atoms and the Nd atoms occupy isolated tetrahedra and dodecahedra, respectively. These polyhedra are connected by the Na atoms, which are located at two different sites, tetrahedral and octahedral. The fluorescence lifetime of the 4 F 3 2 → 4 I 11 2 transition of Nd +3 is reported for the system La 1−x Nd x Na 5 (WO 4 ) 4 . The lifetime of NdNa 5 (WO 4 ) 4 is 85 ± 5 μ sec, which is comparable to NdP 5 O 14 . Concentration quenching is considerably reduced in both host structures, which we conclude is due to the isolation of the rare-earth polyhedra.

Crystal structure of Tl3AsSe3

Abstract The structure of Tl3AsSe3, which has been solved by the single-crystal x-ray method, is rhombohedral, with space group R3m and cell parameters a = 9.870(2) A , c = 7.094(3) A , z = 3 . A full-matrix least-squares refinement gives weighted R = 0.058. The Se atoms form equilateral triangles around Tl at 3.178A and around As at 2.207A. The structure may be described in terms of units formed from three TlSe3 triangles by corner-sharing. These units share corners to produce a helical arrangement along the c axis. The triangles of AsSe3 are isolated from each other.