The non-isothermal devitrification of lithium germanate glasses

The non-isothermal devitrification of lithium germanate glasses, examined by DTA and XRD, is reported and discussed. The glass compositions are expressed by the general formula:xLi₂O(1?x)GeO₂ withx=0.050, 0.125, 0.167, 0.200 and 0.250. All the glasses studied, unlike GeO₂ glass, exhibit internal crystal nucleation without the addition of any nucleating agent. The devitrification processes occur in one or more steps. Phases which crystallized at each step are identified and crystallization mechanisms proposed. These crystallization mechanisms are related to structures of the crystallizing phases. Activation energy values as well as those for glass transition temperatures, do not vary linearly with increase in Li₂O content but pass through a maximum atx=0.200.     

Preparation and characterization of lithium ion-conducting glass-ceramics in the Li1 + xCrxGe2 − x(PO4)3 system

Li₂O–Cr₂O₃–GeO₂–P₂O₅ based glasses were synthesized by a conventional melt-quenching method and successfully converted into glass-ceramics through heat treatment. Experimental results of DTA, XRD, ac impedance techniques and FESEM indicated that Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics treated at 900 °C for 12 h in the Li_1 + xCr_xGe_2 − x(PO₄)₃ (x = 0–0.8) system exhibited the best glass stability against crystallization and the highest ambient conductivity value of 6.81 × 10⁻⁴ S/cm with an activation energy as low as 26.9 kJ/mol. In addition, the Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics displayed good chemical stability against lithium metal at room temperature. The good thermal and chemical stability, excellent conducting property, easy preparation and low cost make it promising to be used as solid-state electrolytes for all-solid-state lithium batteries.     

Die Kristallstruktur der Verbindung Li3Zn0,5GeO4

The crystal structure of the compound Li₃Zn_0.5GeO₄ has been determined and refined by means of three-dimensionalFourier syntheses and least squares. Li₃Zn_0.5GeO₄ crystallizes orthorhombic with space groupD _2h ¹⁶ -Pmnb (No. 62) and the lattice parametersa=6.29,b=10.74 andc=5.17 Å. The crystal structure consists of isolated [GeO₄] tetrahedra, which are linked together by [(Li,Zn)O₄] tetrahedra analogous to Li₃PO₄(h). An additional eight-fold position is partly occupied by two lithium atoms. The occupancy of this position may vary according to the observed range of composition, which lies between Li_3.8Zn_0.1GeO₄ and Li_2.6Zn_0.7GeO₄.

     

Thermal properties and stability of lithium titanophosphate glasses

DTA was used to study thermal properties and thermal stability of (50-x)Li₂O-xTiO₂-50P₂O₅ (x=0–10 mol%) and 45Li₂Ot-yTiO₂-(55-y)P₂O₅ (y=5–20 mol%) glasses. The addition of TiO₂ to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO₃, Li₄ P₂O₇, TiP₂O₇ and NASICON-type LiTi₂(PO₄)₃. DTA results also indicated that the maximum of nucleation rate for 45Li₂O-5TiO₂-50P₂O₅ glass is close to the glass transition temperature.     

Ein neues Oxogermanat: Li8GeO6 = Li8O2[GeO4]. (Mit einer Bemerkung über Li8SiO6 und Li4GeO4)

A New Oxogermanate: Li₈GeO₆ ? Li₈O[GeO₄] Transparent colourless single crystals of Li₈GeO₆(P6₃cm, a = 550.09(8), c = 1072.2(3) pm, Z = 2; 4-circle-diffractometer Siemens AED 2, MoKα; 326 I_o(hkl), R = 2.4%, R_w = 2.0%), have been prepared. As by-product we always got colourless isometric single crystals of Li₄GeO₄. For the first time we could grow single crystals of Li₈SiO₆ of suitable size and quality. Our structure refinement confirms the assumed structure model [2]: Li₈GeO₆ and Li₈SiO₆ are isotypic with Li₈CoO₆[3] (Li₈SiO₆: a = 542.43(8), c = 1062.6(2) pm, Z = 2; 4-circle-diffractometer Siemens AED 2, MoK_α; 306 I_o(hkl), R = 3.6%, R_w= 3.0%). The known crystal structure of Li₄GeO₄ [4] is confirmed and refined (Cmcm, a = 776.6(2), b = 735.7(3), c = 604.9(2) pm, Z = 4; 4-circle-diffractometer Siemens AED 2, MoKα, 298 I_o(hkl), R = 1.9%, R_w = 1.4%). The Madelung Part of Lattice Energy, MAPLE, and Effective coordination-Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated.     

Revised phase diagram of Li2MoO4-ZnMoO4 system, crystal structure and crystal growth of lithium zinc molybdate

Orthorhombic lithium zinc molybdate was first chosen and explored as a candidate for double beta decay experiments with ¹⁰⁰Mo. The phase equilibria in the system Li₂MoO₄-ZnMoO₄ were reinvestigated, the intermediate compound Li₂Zn₂(MoO₄)₃ of the α-Cu₃Fe₄(VO₄)₆ (lyonsite) type was found to be nonstoichiometric: Li_2−2xZn_2+x(MoO₄)₃ (0≤x≤0.28) at 600 °C. The eutectic point corresponds to 650 °C and 23 mol% ZnMoO₄, the peritectic point is at 885 °C and 67 mol% ZnMoO₄. Single crystals of the compound were prepared by spontaneous crystallization from the melts and fluxes. In the structures of four Li_2−2xZn_2+x(MoO₄)₃ crystals (x=0; 0.03; 0.21; 0.23), the cationic sites in the face-shared octahedral columns were found to be partially filled and responsible for the compound nonstoichiometry. It was first showed that with increasing the x value and the number of vacancies in M3 site, the average M3-O distance grows and the lithium content in this site decreases almost linearly. Using the low-thermal-gradient Czochralski technique, optically homogeneous large crystals of lithium zinc molybdate were grown and their optical, luminescent and scintillating properties were explored.     

Die Kristallstruktur von Li2GeO3

Zusammenfassung Die Kristallstruktur von Li₂GeO₃ wird mit Hilfe dreidimensionalerFourier-Synthesen und nach der Methode der kleinsten Quadrate bestimmt. Li₂GeO₃ ist isotyp mit Li₂SiO₃ und enthält [GeO₃]^2–-Ketten (Zweiereinfachkette). Die Gitterparameter der rhombischen Elementarzelle (C _2v ¹² –Cmc2₁) betragen:a=9,63₀,b=5,46₅ undc=4,85₀ Å. Als mittlere interatomare Abstände wurden erhalten: Ge–O=1,74 und Li–O=2,01 Å.

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The crystal structure of Li₂GeO₃ has been determined by means of 3-dimensional Fourier syntheses and least-squares method. Li₂GeO₃ is isostructural with Li₂SiO₃, containing [GeO₃]^2–-chains (Zweiereinfachkette). The lattice parameters of the orthorhombic cell (C _2v ¹² –Cmc2₁) are:a=9,63₀;b=5,46₅ andc=4,85₀ Å. The average interatomic distances are found to be: Ge–O=1,74 and Li–O=2,01 Å.

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Mit 3 Abbildungen     

An Unexpected New Member of the Family of Lithium Oxonitridosilicates – Li7Si2NO6

With Li₇Si₂NO₆, a new member of the family of lithium oxonitridosilicates with a so far unseen structure type could be synthesized. Using a high-temperature solid-state reaction in open nickel crucibles under nitrogen flow, it was possible to obtain single crystals from the starting materials SiO₂, Li₃N, and Li₂O at temperatures of 900 °C. Single crystal X-ray diffraction data yielded lattice parameters of a=5.0934(2), b=7.4128(2), c=8.5918(2) Å, α=75.16(1)°, β=87.36(1)°, γ=73.01(1)° and a cell volume of V=299.75(2) ų. The compound, crystallizing in the triclinic space group P (no. 2), consists of a highly condensed anionic network built up by [SiNO₃]-, [LiO₄]-, and [LiN₂O₂]-tetrahedra as well as lithium in octahedral coordination as completing cation. With an activation barrier of 695 meV for lithium migration, Li₇Si₂NO₆ is a potential lithium-ion conductor. The structure allows a classification not only as a sorosilicate but also as a tecto-lithosilicate and most precisely as a lithium oxonitridolithosilicate, when the different coordinations of the lithium ions are taken into account. Interestingly, the new compound is none of the several proposed representatives of the lithium oxonitridosilicates, thus expanding this substance class unexpectedly.     

Die Kristallstruktur des Lithiumheptagermanats Li2[Ge7O15]

Zusammenfassung Die Kristallstruktur der Verbindung Li₂[Ge₇O₁₅] wird mit Hilfe dreidimensionaler Patterson- und Fourier-Synthesen bestimmt und nach der Methode der kleinsten Quadrate verfeinert. Die Gitterparameter der orthorhombischen Elementarzelle (Pbcn — D _2h ¹⁴ ) betragen:a=7,36,b=16,76 undc=9,69 Å. Die Struktur enthält stark gewellte Schichten aus [GeO₄]-Tetraedern, die über [GeO₆]-Oktaeder zu einem dreidimensionalen Gerüst verknüpft sind; sie läßt sich durch die Formel Li₂[Ge(Ge₂O₅)₃] charakterisieren. Als mittlere Ge–O-Abstände werden erhalten: 1,735 Å (K.Z. 4) und 1,893 Å (K.Z. 6).

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The crystal structure of Li₂[Ge₇O₁₅]

The crystal structure of Li₂[Ge₇O₁₅] has been determined by means of three-dimensional Patterson and electron density syntheses, and refined by least-squares method. The lattice parameters of the orthorhombic unit cell (Pbcn-D _2h ¹⁴ ) are:a=7.36,b=16.76 andc=9.69 Å. The crystal structure contains strongly puckered layers of [GeO₄]-tetrahedra linked by [GeO₆]-octahedra to form a three-dimensional framework; the structure can be characterized by the formula Li₂[Ge(Ge₂O₅)₃]. The averaged Ge–O-distances are found to be: 1.735 Å (c. n. 4) and 1.893 Å (c.n. 6).

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Mit 1 Abbildung     

Electronic polarizability and crystallization of K2O-TiO2-GeO2 glasses with high TiO2 contents

Some K₂O-TiO₂-GeO₂ glasses with a large amount of TiO₂ contents (15-25 mol%) such as 25K₂O-25TiO₂-50GeO₂ have been prepared, and their electronic polarizability, Raman scattering spectra, and crystallization behavior are examined to clarify thermal properties and structure of the glasses and to develop new nonlinear optical crystallized glasses. It is proposed that the glasses consist of the network of TiO₆ and GeO₄ polyhedra. The glasses show large optical basicities of Λ=0.88-0.92, indicating the high polarizabity of TiO_n (n=4-6) polyhedra in the glasses. K₂TiGe₃O₉ crystals are formed through crystallization in all glasses prepared in the present study. In particular, 20K₂O-20TiO₂-60GeO₂ glass shows bulk crystallization and 18K₂O-18TiO₂-64GeO₂ glass exhibits surface crystallization giving the c-axis orientation. The crystallized glasses show second harmonic generations (SHGs), and it is suggested that the distortion of TiO₆ octahedra in K₂TiGe₃O₉ crystals induces SHGs.     

Die Kristallstruktur der Verbindung LiNa[Ge4O9]

Zusammenfassung Die Kristallstruktur der Verbindung LiNa[Ge₄O₉] wird durch dreidimensionale Patterson- und Fourier-Synthesen bestimmt und mit Hilfe der Methode der kleinsten Quadrate verfeinert. Die rhombische Elementarzelle (Pcca-D _2h ⁸ ) mit den Abmessungen:a=9,31,b=4,68,c=15,88 Å enthält 4 Formeleinheiten. Die Struktur wird aus [GeO₃] _n -Ketten mit tetraedrisch koordiniertem Germanium aufgebaut, die über [GeO₆]-Oktaeder zu einem dreidimensionalen Gerüst vernetzt sind. Als mittlere interatomare Ge-O-Abstände wurden erhalten: 1,758 [4] und 1,866[6] Å. Die Verbindung LiNa[Ge₄O₉] stellt ein Endglied der Mischreihe Li_2–x Na _x [Ge₄O₉] dar.

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Crystal structure of LiNa[Ge₄O₉]

The crystal structure of LiNa[Ge₄O₉] has been determined by means of three-dimensional Patterson and electron density syntheses and refined by least-squares methods. The orthorhombic unit cell (Pcca-D _2h ⁸ ) having the lattice parametersa=9.31,b=4.68 andc=15.88 Å contains 4 formula units. The crystal structure consists of [GeO₃] _n -chains of tetrahedrally coordinated Ge-atoms which are connected by [GeO₆]-octahedra to form a three-dimensional framework. The interatomic Ge-O-distances are found to be 1.758[4] and 1.866[6] Å. The compound LiNa[Ge₄O₉] represents a member of the solid solution series Li_2–x Na _x [Ge₄O₉].

     

Crystal Structures of Double Vanadates LiCoVO4 and Li0.5Co1.25VO4

The crystal structures of vanadates Li_1-2xCo_1+xVO₄ with x = 0 and 0.25 have been studied by a full pattern analysis. It has been shown that in cubic spinel LiCoVO₄ (space group Fd3m), the 8a tetrahedral sites contain a majority of vanadium and a small amount of lithium; all cobalt, lithium, and a small amount of vanadium occupy the 16d octahedral sites. Li_0.5Co_1.25VO₄ crystals belong to the rhombic system (Imma space group) with unit cell parameters a = 5.939(1), b = 5.810(1), and c = 8.303(1). On substitution of lithium by cobalt according to the scheme 2Li⁺ Co²⁺ + , half of the lithium and 70% of the vacancies formed are in the 4a octahedral sites, and onethird of lithium and most of cobalt occupy the 4d octahedral sites. The 4e tetrahedral sites are completely occupied by vanadium and lithium in a ratio of 0.92/0.08. The interatomic distances in LiCoVO₄ and Li_0.5Co_1.25VO₄ are calculated, and the sizes of lithium ion transport channels are evaluated.     

Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra

The new stannide Li₂AuSn₂ was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li₂AuSn₂ was investigated by X‐ray diffraction on powders and single crystals and the structure was refined from single‐crystal data: Z=4, I4₁/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F² values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au? Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two‐dimensional AuSn_4/2 layers. The latter are connected in the third dimension through Sn? Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three‐dimensional [AuSn₂] network. Modestly small ⁷Li Knight shifts are measured by solid‐state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the ¹¹⁹Sn Mössbauer spectra and a small chemical shift anisotropy evident from ¹¹⁹Sn solid‐state NMR spectroscopy. Variable‐temperature static ⁷Li solid‐state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature‐dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol^?1.     

Solid lithium electrolytes based on Fe3+-modified lithium orthogermanate

Solid lithium electrolytes in the Li_4-3x Fe _x GeO₄ system were synthesized. Their phase composition, thermal behavior, and electrical conductivity were studied in the temperature interval 300–750°C. Introduction of Fe³⁺ ions into lithium orthogermanate leads to the formation of a γ-Li₃PO₄-type structure and to a sharp increase in the conductivity, with a maximum reached at x = 0.075–0.15: about 10^?1 S cm^?1 at 300°C and more than 1 S cm^?1 at 700°C. The main current carriers are interstitial Li⁺ cations weakly bound with the rigid framework. Owing to high conductivity, the electrolytes studied are of interest for use in high-temperature electrochemical devices.     

Synthesis and thermal characterization of NZP compounds Na1?xLixZr2(PO4)3 (x?=?0.00–0.75)

Sodium zirconium phosphate (NZP) composition Na_1−x Li _x Zr₂(PO₄)₃, x = 0.00–0.75 has been synthesized by method of solid state reaction method from Na₂CO₃·H₂O, Li₂CO₃, ZrO₂, and NH₄H₂PO₄, sintering at 1050–1250 °C for 8 h only in other to determine the effect on thermal properties, such as the phase formation of the compound. The materials have been characterized by TGA and DTA thermal analysis methods from room temperature to 1000 °C. It was observed that the increase in lithium content of the samples increased thermal stability of the samples and the DTA peaks shifted towards higher temperatures with increase in lithium content. The thermal stability regions for all the sample was observed to be from 640 °C. The sample with the highest lithium content, x = 0.75, exhibited the greatest thermal stability over the temperature range.     

Lithium-cationic conductivity in the Li4 − 2x Cd x GeO4 system

The lithium-conducting solid electrolytes in the Li_{4 ? 2x} Cd _x GeO₄ (0 ≤ x ≤ 0.6) system are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The specimens with the highest conductivity have a γ-Li₃PO₄-derivative structure. The solid solutions with x = 0.15–0.25 are stable at the room temperature, whereas the specimens with x ≥ 0.3 decompose yielding Li₂CdGeO₄ below 310 ± 10°C. Li_3.6Cd_0.2GeO₄ solid solution exhibits the highest conductivity (5.25 × 10^?2 S cm^?1 at 300°C). The factors, which affect the conductivity of synthesized solid electrolytes, are considered.     

Ion trapping and its effect on the conductivity of LISICON and other solid electrolytes

Conductivity data for the lithium ion conducting solid electrolyte, LISICON, Li_2+2xZn_1?xGeO₄ over a particularly wide composition range, 0.15 < x < 0.85, and over the temperature range ～25 to 150°C show that both the activation energy and preexponential factor pass through maxima around x ～ 0.4 to 0.5, at which the preexponential factor exhibits anomalously high values, ～10¹³ ohm^?1 cm^?1 K. An explanation is offered which involves the trapping of mobile Li⁺ ions by the immobile sublattice at lower temperatures. This model also accounts for ageing effects observed at lower temperatures in which the conductivity decreases slowly with time. In the isostructural Li⁺ electrolytes, Li_3+xSi_xY_1?xO₄ (Y = P, As, V), the compositional dependence of both the preexponential factor and activation energy is less marked and no evidence for ion trapping effects is observed.     

Studies on Li2SO4-MgSO4 and Li2SO4-Li4SiO4 systems

The phase equilibria as well as the properties and crystal structures of the compounds formed in both Li₂SO₄-MgSO₄ and Li₂SO₄-Li₄SiO₄ systems have been studied by means of x-ray diffraction technique (at high and room temperatures) as well as by the thermal analyses (DTA, DSC, TGA, etc.). In Li₂SO₄-MgSO₄ system there exists a compound Mg₄Li₂(SO₄)₅ formed by peritectic reaction at 840°C and decomposed at 105°C into the Li₂SO₄-base solid solution and MgSO₄ · Mg₄Li₂(SO₄)₅ and Li₂SO₄-base solid solution conduct an eutectic reaction at 663°C with the composition of eutectic point lying in 22 mol% MgSO₄. The solubility of MgSO₄ in Li₂SO₄ is a little smaller than 10 mol% while at the same time the Li₂SO₄ phase transition temperature decreases from 574 to 560°C On the other hand, no noticeable solid solubility of Li₂SO₄ in MgSO₄ has been observed. The reaction is an endothermal one and its heat of formation is 2.57 kJ/mol. The activation energy of the reaction calculated by thermal peak displacement method at various heating rates is 173.5 kJ/mol (1.80 ev). The crystal Mg₄Li₂(SO₄)₅ belongs to orthorhombic system with lattice parameters at 180°C: a = 8.577, b=8.741, c= 11.918 Å. The space group seems to be either P222 or P mmm. Assuming that there are two formula units in a unit cell, the density calculated is then 2.20 g/cm³ very close to that of Li₂SO₄ or MgSO₄. Meanwhile, in Li₂SO₄-Li₄SiO₄ system a new phase Li_8-2x(SiO₄)_8-x(SO₄)_x is formed by peritectic reaction at 953°C with a range of composition x=0.96 ?0.58. The crystal belongs to ortho-rhombic system with lattice parameters at x=0.8: a = 5.002, b= 6.173 and c=10.608Å. The density observed is 2.31 g/cm³ and there are 2 formula units in an unit cell. It is shown from the measurements of piezoelectric and laser SHG coefficients of the crystal that the crystal posseses a symmetrical center with the space group belonging to P mmn. The lattice parameter c has a maximum at x=0.8. In the air Li_8-2x(SiO₄)_2-x(SO₄)_x can absorb 7.6 wt% water vapour and other gases which can only be desorbed by heating it at a temperature above 350°C. Neither absorption nor desorbtion can change its crystal structure, a characteristic similar to that of zeolite molecular sieve. The dewater activation energy of Li_8-2x(SiO₄)_2-x(SO₄)_x is 171.5 kJ/mol. Li_8-2x(SiO₄)_2-x(SO₄)_x and Li₄SO₄ bring about an eutectic reaction at 823°C with its eutectic composition being 12 mol% Li₄SiO₄. No observable solubility of Li₄SiO₄ in Li₃SO₄ has been noticed. The solubility of Li₂SO₄ in Li₄SiO₄ is approximately equal to 5 mol%. With Li₂SO₄ being dissolved in, the phase transition temperature of Li₄SiO₄ is decreased. After being fused, the specimens Li₃SO₄-MgSO₄ and Li₂SO₄-Li₄SiO₄ are cooled at a rate of 10°C/min, their metastable eutectic systems are resulted respectively.     

Lithium aluminate-doped lithium orthosilicate: Sol-gel ceramics and lithium dynamics

Dense ceramics (Li_4+xSi_1−xAl_xO₄ with 0 ≤ x ≤ 0.3) are obtained by sintering at 700–900°C, without prior calcination, of sol-gel powders prepared by an alkoxide-hydroxide route. In comparison with the pure lithium orthosilicate (3 × 10⁻⁴ S · cm⁻¹ at 350°C), only a slight enhancement of the ionic conductivity is noted for monophase ceramics with Li₄SiO₄-type structure (5 × 10⁻⁴ S · cm⁻¹ at 350°C for x = 0.3). Higher conductivity (2 × 10⁻² S · cm⁻¹ at 350°C) is observed for an heterogeneous material formed of a lithium silicoaluminate phase (x = 0.2) with the Li₄SiO₄-type structure coexisting with lithium hydroxide. In this two-phase material, ac conductivity and ⁷Li spin-lattice relaxation data are consistent with the formation of a new kinetic path, via a thin layer along the interface, which enhances the lithium mobility.     

Synthesis,crystal structures and chemical bonding of RE5−xLixGe4 (RE = Nd,Sm and Gd; x≃ 1) with the orthorhombic Gd5Si4 type

The syntheses and single‐crystal and electronic structures of three new ternary lithium rare earth germanides, RE_5−xLi_xGe₄ (RE = Nd, Sm and Gd; x≃ 1), namely tetrasamarium lithium tetragermanide (Sm_3.97Li_1.03Ge₄), tetraneodymium lithium tetragermanide (Nd_3.97Li_1.03Ge₄) and tetragadolinium lithium tetragermanide (Gd_3.96Li_1.03Ge₄), are reported. All three compounds crystallize in the orthorhombic space group Pnma and adopt the Gd₅Si₄ structure type (Pearson code oP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4c and Ge3 in 4c. One of the RE sites, i.e. RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE₄LiGe₄ stoichiometry.