Garnet Family Research Articles

Near-infrared luminescence in Ca3ZnMGe3O12:Cr3+ (M = Zr, Hf, Sn, Ti) garnet family for light-emitting diode applications

Near-infrared (NIR) phosphors as crucial components of NIR light sources have multifunctional and smart spectroscopy applications, prompting an increasing research interest in developing efficient and stable NIR materials. Focusing on this issue, the present study explored the luminescent properties of Cr3+-doped Ca3ZnMGe3O12 (M = Zr, Hf, Sn and Ti) garnet family. These materials exhibit an emission peak falls within the range of 785–805 nm with a full width at half maximum (FWHM) varying from 114 to 123 nm. Among them, the Ca3ZnZrGe3O12:Cr3+ phosphor shows the highest photoluminescence quantum yield (PLQY = 60.3 %) and an excellent thermal stability (I423K/I298K = 77.51 %). Moreover, the performance of a prototype Ca3ZnZrGe3O12:Cr3+-containing NIR pc-LED device was estimated, which achieves an NIR output of 23.46 mW and a photonic efficiency of 14.09 % under 100 mA driving current. Non-destructive examination can be realized using this light source, demonstrating the good potential of the material in NIR spectroscopy applications.

DFT calculations of the stability field and properties of a predicted lanthanum–scandium–aluminum garnet La[formula omitted]Sc[formula omitted]Al[formula omitted]O12 and P–T phase diagram of Y[formula omitted]Sc[formula omitted]Al[formula omitted]O12

In this study we present the results of our density functional theory calculations within the quasi-harmonic approximation, which predict formation and properties of a new compound of the garnet family, La3Sc2Al3O12 (LSAG). LSAG was shown to be formed from 3LaAlO3 + Sc2O3 at ambient pressure and room temperature. The thermodynamic stability region of LSAG is limited by a temperature of 685 K, above which its decomposition into LaAlO3 (LAP) and Sc2O3 occurs. With increasing pressure, LSAG retains its stability up to 0.23 GPa, where the decomposition reaction LSAG↔3LAP＋ Sc2O3 becomes thermodynamically favorable. In this work, not only the thermodynamic stability of LSAG was assessed, but also its thermal conductivity, elastic constants and band gap were calculated. At 300 K the thermal conductivity of LSAG is 13.204 Wm−1K−1. LSAG has the smallest elastic constants compared with YSAG and YAG, which indicates weaker atomic bonding in LSAG than in YSAG and YAG. The width of band gap of LSAG calculated using an hybrid functional is equal to 5.24 eV. In addition, the P–T phase diagram of the known Y3Sc2Al3O12 (YSAG) was calculated for the first time. Unlike LSAG, YSAG is stable at fairly high temperatures, reaching values of at least 1500 K. With increasing temperature to 1500 K, the pressure of the phase transition increases slightly to 3.55 GPa, and the monovariant curve of the reaction YSAG↔3YAP+Sc2O3 is represented by an almost straight line.

Interrupting the long-range energy migration among Eu3+ by the introduction of unequivalent [NaO8] units to achieve both high quenching concentration and quantum yield in NaY2Ga2InGe2O12

In the pursuit of optimizing white light-emitting diodes (WLEDs), Eu3+-doped phosphors have emerged as a key component in strategies that combine ultraviolet (UV) LED chips with red, green, and blue (RGB) tricolor phosphors. However, their application has been notably constrained by concentration quenching and thermal quenching. To address this challenge, we have developed a series of novel red phosphors, NaY2-xGa2InGe2O12:xEu3+. The powder X-ray diffraction (XRD) indicates that the NaY2Ga2InGe2O12(NYGIG) belongs to the garnet family. The [NaO8] unit replaces one-third of the eight-coordinated sites of garnet and leaves the other two-thirds for the [YO8], which helps to prevent long-range energy migration among Eu3+ especially when the eight-coordinated sites were highly substituted. Such a structure feature allowed the NaY2-xGa2InGe2O12:xEu3+ phosphor to achieve an optimal quantum yield of 95.6% at an extremely high Eu3+ doping x value up to 1.2. Moreover, further studies on the temperature-dependent luminescence spectra confirm that an anomalous thermal quenching phenomenon will occur when the NaY2-xGa2InGe2O12:1.2Eu3+ phosphor is properly excited. In application, the combination of the red-emitting NaY2-xGa2InGe2O12:1.2Eu3+, blue-emitting BaMgAl10O17:Eu2+, and green-emitting Zn2SiO4:Mn2+ phosphors can realize high color rendering (CRI∼93) white light with the with CIE coordinates of (0.353,0.350), indicating that the NYGIG:Eu3+ phosphor own a promising potential for WLEDs.

Composite solid electrolytes based on Li7La3Zr2O12 for all-solid-state lithium power sources

Currently development of all-solid-state lithium batteries are in great demand all over the world. Li7La3Zr2O12 (LLZ) compounds are considered as perspective solid electrolyte for such power sources. However, these solid electrolytes of garnet family have some disadvantages – high temperatures of ceramic synthesis, poor wettability by Li and low stability to air components. The creation of composite solid electrolytes based on LLZ is one of the ways to solve these problems. It was established that the temperature and/or sintering time of the solid electrolyte could be reduced by the introduction of different additives with maintaining lithium-ion conductivity values (10–5–10–4 S/cm at room temperature). It should be noted that the used sintering additive should meet the following requirements: low softening temperatures, high values of lithium-ion conductivity, stability in contact with lithium metal and absence of chemical interaction between components leading to the formation of low-conductivity impurity phases. Thus, the development of composite solid electrolytes based on LLZ is perspective for all-solid-state power sources.

A review Synthesis and luminescence characterize of emitting phosphor of garnet structure with effect of heating time

In this review, we deal with the structural properties of the garnet family of phosphor materials activated with trivalent lanthanide ions in the nano-crystalline materials. The interest is devoted the important garnet hosts: structure and luminescence spectroscopy are presented and discussed with particular meanings given to the possibility of achieving efficiently luminescence from trivalent lanthanide ions at the nano-level and to the potential and predicted technological applications of this class of materials.

Discovery of high entropy garnet solid-state electrolytes via ultrafast synthesis

Multi-elemental functional oxides are crucial for addressing global energy challenges. High entropy oxides (HEO) represent an emerging class of such materials with exceptional performance, attracting significant attention in energy research. However, the concept of high entropy exponentially expands the exploration space of related materials, making the design and discovery of high-performance HEO a challenging task. The synthesis of HEO through a highly efficient and reproducible manner is urgently needed to understand their structure-property relations and develop high-performance materials. In this study, we achieved the ultrafast synthesis of high-entropy garnet Li7+a-c-2dLa3(A3+aB4+bC5+cD6+d)O12 (A=Sc, Y, Bi; B=Zr, Mo, Sn, Te, Hf; C=Nb, Sb, Ta; D=W) in merely tens of seconds. Among the various garnets ranging from unary-garnet to denary-garnet, the quinary-garnet (Li6.6La3Zr0.4Sn0.4Sc0.4Ta0.4-Nb0.4O12) exhibits the highest ionic conductivity (3.57 × 10−4 S cm−1) and low electronic conductivity (5.26 × 10−9 S cm−1), with a high critical current density (2.4 mA cm−2) in symmetrical cells. Furthermore, via high-throughput screening of the garnet family, we discover the entropy-stabilization effect, where the synthesized garnet products are gradually stabilized into the desired pure cubic phase with increased configuration entropy. Our work demonstrates a significant step towards the rapid and accurate discovery of high-performance energy materials in the vast multi-elemental material space.

Frustrated Magnet Mn3Al2Ge3O12 Garnet: Crystal Growth by the Optical Floating Zone Method

Mn3Al2Ge3O12 is a member of the garnet family of compounds, A3B2(CO4)3, whose magnetic properties are affected by a high degree of geometrical frustration. The magnetic frustration is at the origin of the intriguing magnetic properties that these materials exhibit, such as a long range hidden order derived from multipoles formed from 10-spin loops in the gadolinium gallium garnet, Gd3Ga5O12. Mn3Al2Ge3O12 garnet is isostructural to the thoroughly investigated Gd garnets, Gd3Ga5O12 and Gd3Al5O12. Moreover, in Mn3Al2Ge3O12, the Heisenberg-like Mn2+ magnetic ions (L= 0) are also arranged in corner sharing triangles that form a hyperkagomé structure. The identical crystallographic structures and similar Heisenberg-like behaviour of the magnetic ions make manganese aluminium germanium garnet the closest compound to the gadolinium garnets in its magnetic properties. Here, we report, for the first time, the growth of a large, high quality single crystal of the Mn3Al2Ge3O12 garnet by the floating zone method. X-ray diffraction techniques were used to characterise and confirm the high crystalline quality of the Mn3Al2Ge3O12 crystal boule. Temperature-dependent magnetic susceptibility measurements reveal an antiferromagnetic ordering of the Mn2+ ions below TN= 6.5 K. The high quality of the single crystal obtained makes it ideal for detailed investigations of the magnetic properties of the system, especially using neutron scattering techniques.

An efficient and thermally stable near-infrared phosphor derived from the Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) garnet family.

A broadband near-infrared (NIR) light source based on a phosphor-converted light-emitting diode (pc-LED) has attracted increasing interest to be used in non-destructive examination, security-monitoring and medical diagnosis fields, which stimulates the exploration of NIR phosphors with high performance. Herein, a series of Cr3+-activated garnet Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) phosphors were reported, allowing an emission peak ranging from 726 to 822 nm. Among them, Y3ScInGa3O12:Cr3+ with an optimized Cr3+-doping concentration of 6 mol% exhibits a high internal quantum efficiency (IQE = 83.1%) and excellent absorption efficiency (AE = 44.2%) under 450 nm blue light excitation, enabling an external quantum efficiency as high as 36.7%. Moreover, this material can maintain 93.0% of the initial intensity when heated up to 423 K, implying outstanding thermal stability. Finally, a prototype NIR pc-LED device was fabricated by coating the optimized phosphor on a 455 nm LED chip, which generates a broadband NIR emission with a peak located at 765 nm and a full width at half maximum of 127 nm. The NIR output power and NIR photoelectric conversion efficiency of this device were found to be 38.01 mW and 11.0%, respectively, under 100 mA driving current, demonstrating the feasibility of this material to be applied in NIR pc-LEDs.

5V Solid-State Lithium Batteries Using Garnet-Based Electrolytes and LiNi0.5Mn1.5O4 Spinel Cathode Composite

There is an ever increasing demand to increase the gravimetric and volumetric energy density of Lithium batteries as well as enhancing their safety cycle life and lower safety. Solid-State batteries (SSB) enjoy a great attention nowadays due to their potential to meet all those requirements and power the EV revolution. The use of solid electrolytes (SE) in commercial batteries has been solely limited to polymer electrolytes based on poly(ethylene oxide), PEO, coupled with LiFePO4 (LFP) that are limited by the oxidative stability of PEO to < 3.6 V and the low potential of LFP at 3.4 V. The commercial cells are cycled at high temperature (45 ⁰C) to overcome the modest ambient ionic conductivity of the SE and under a stack pressure and a cathode composite to overcome the high interfacial resistances of the solid-solid interfaces. A cathode composite is made of conventional cathode components with a "catholyte" added to the formulation. The catholyte is made of an optimized amount of an ionic conductor that is mostly derived from the solid electrolyte formulation. Very recent studies by our research group (1) and others (2) have shown that higher voltage cells can be made by using garnet or perovskite-based ceramic/polymer composites and LiNi0.5Mn0.3Co0.2O2 (NMC532) or LiNi0.6Mn0.2Co0.2O2 (NMC 622) layered cathodes reaching 4.2 V and can operate for few cycles. Herein, we extend the work in order to further increase the voltage of the SSB cells by using LiNi0.5Mn1.5O4 (LNMO) spinel cathode with its high potential of 4.7 V. The Tantalum-doped Lithium Lanthanum Zirconate, Li6.4La3Zr1.4Ta0.6O12 (Ta-doped LLZO, LLZTO), of the garnet family of solid electrolytes has been selected as a SE due to their high ambient ionic conductivity, wide electrochemical stability window and good chemical stability against Li metal. PEO and other compatible polymers have been used to formulate composite SEs in thin films and their properties were studied and compared with LLZTO pellets. Cells have been made using composite cathode formulations composed of LNMO cathode as an active material, carbon black, conventional and novel binders and a SE-based and proprietary catholyte coupled with the SE films or pellets and thick/thin Li films. The short-term cycling performance of the cells assembled with selected SEs and composite cathodes along with other electrochemical results will be presented.

Oxygen nonstoichiometry effects in spin Seebeck insulating Y3−xPrxFe5O12+ δ materials

Yttrium iron garnet (Y3Fe5O12) and its derivatives are ferrimagnetic spin Seebeck insulating materials crucial for the spin transport based phenomena such as the spin Seebeck effect (SSE) and spin Hall magnetoresistance. Structure–property correlation studies of such materials under different conditions are useful for optimizing the relevant constraint in the existed phenomena. The usage of Y3Fe5O12 type materials over the broad range of temperature conditions (27–450 °C) in SSE is under study. We report here the structure–property correlation in spin Seebeck insulating Y3−xPrxFe5O12+δ oxides as a representative material and introduce the additional degrees of freedom in the crystal system relevant to the spin transport based phenomena under high temperature conditions. The natural tendency of having oxygen nonstoichiometry in an iron garnet family of materials strengthens the Fe–O–Fe superexchange interaction, which, in turn, tends to increase the spin voltage correlated magnetic parameters. The analysis of experimental high temperature neutron diffraction data (over 27–450 °C) reveals the oxide ion nonstoichiometry and excess oxide ion transport pathways at moderate temperature 150 °C in the crystal lattices of studied garnet materials. Oxide ion nonstoichiometry, ionic transport, and electron hopping in crystal lattices cause a tremendous variation of electrical conductivity (10−11–10−2 S cm−1) over a moderate change of temperature (27–450 °C). The occurrence of electrical transport in the required thermal gradient over the garnet material in SSE can evoke the additional degrees of freedom in the usage of such materials at high temperatures. The present work provides a new outlook in terms of structure–property correlation for spin transport based materials.

Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method

AbstractThe research conducted herein builds upon the achievement of a successful and stable 170 × 300 × 35 mm YAG and 5% Yb:YAG single‐crystals production via the horizontal directed crystallization method. Based on the analysis of residual birefringence pattern in analyzed ingots, a hypothesis is proposed—debating that in certain stages of the growth, {211} facets start to form within some sections of the crystallization front. The sensitivity of the {211} facets to temperature fluctuations seems to cause striations in the facets’ growth sectors. In a later stage of the growth process the slope of the crystallization front naturally changes, which seems to reduce the formation of facets considerably. As a result, the rear part of the crystal achieves the best optical quality. The samples extracted from that portion of the ingot, after annealing, possess good optical quality and heat release of 0.004 1/m at 1070 nm, which is quite low, and is considered a good result for the garnet family of crystals. The lasing experiment with thin‐disk geometry shows a slope efficiency of 52% and proves that the material is suitable for high‐power lasers application.

Novel orange-red-emitting Li5+xCaxLa3-xTa2O12:Sm3+ (x = 0; 1) phosphors: Crystal structure, luminescence and thermal quenching studies

The novel lithium tantalates doped with samarium ions were prepared using the solid state method. The single-phase Li5+xCaxLa3-xTa2O12:Sm3+ (x = 0; 1) compounds crystallize in the cubic space group Ia3‾d (Z = 8) and belong to the garnet family which is used for various optical applications. The diffuse reflectance, excitation and photoluminescence spectra measured at room and elevated temperatures are discussed in detail. The compounds demonstrate the well-known orange-red emission associated with the 4f-4f transitions in Sm3+ ions. The optimum samarium content in Li6CaLa2-xSmxTa2O12 solid solution is equal to 3 mol%, and the quenching mechanism is caused by the dipole-dipole interaction. Li6CaLa2-xSmxTa2O12 series provides higher luminescence intensity in comparison with Li5La3-xSmxTa2O12 samples. The CIE chromaticity coordinates are almost identical for all compounds and are equal to (0.61, 0.39). The Li6CaLa2Ta2O12:Sm3+ phosphors have good thermal stability of emission which allows one to consider these lithium calcium tantalate garnets as potential orange-red-emitting phosphors.

A test of bolometric properties of Tm-containing crystals as a perspective detector for a solar axion search

The $^{169}$Tm nuclide has first nuclear level at 8.41 keV with magnetic type transition to the ground state and, therefore, can be used as a target nucleus for the search of resonant absorption of solar axions. We plan to use a Tm-containing crystal of a garnet family Tm$_3$Al$_5$O$_{12}$ as a bolometric detector in order to search for the excitation of the first nuclear level of $^{169}$Tm via the resonant absorption of solar axions. With this perspective in mind, a sample of the Tm$_3$Al$_5$O$_{12}$ crystal was grown and tested for its bolometric and optical properties. Measurements of chemical and/or radioactive contaminations were performed as well. In this paper we present the test results and estimate the requirements for a future low-background experimental setup.

Impact of Processing Conditions on Oxygen Vacancies in Ga-Doped Li7La3Zr2O12 Solid Electrolyte Using Tof-SIMS

Currently a vast amount of research into fast lithium ion conductors is taking place for application into solid electrolytes. The most attractive compositions being from the garnet family with the chemical composition of Li7La3Zr2O12 [1]. LLZO has high lithium ion mobility at room temperature, a large electrochemical window which allows high voltage cathodes to be employed and good stability with lithium metal anodes. Typically, LLZO is doped at the lithium position with donor cations these include Al3+and Ga3+ which provide stability of the cubic crystal phase thus allowing Li+ mobility in three dimensions. The mobility for Ga-LLZO has been reported to be above 10-3 S.cm-1 [2], [3] this is the composition that will be mainly focused on in the poster. Preliminary investigations have shown that due to lithium loss during high processing temperatures oxygen vacancies are formed because of the charge compensation mechanism[4]. The quantification of oxygen vacancies as an affect of the processing conditions and it effect on the conductivity of oxygen and lithium ions have been investigated in this work using electrochemical impedance spectroscopy and cell cycling. The affect of different densification atmospheres (Ar, Vac, and O2) on oxygen vacancies are measured using 18O isotopic labelling coupled with the Time of Flight Secondary Ion Mass Spectrometer (ToF-SIMS) to assess which results in a higher degree of oxygen defects. This work will be correlated with lithium defect chemistry and mobility to understand the lithium critical current density for dendrite growth which are detrimental to battery life.

Non-proportionality and energy resolution of LuxY1-xAG:Pr and LuAG:Pr,Mo crystals

Praseodymium activated lutetium aluminum garnet (LuAG:Pr) is an inorganic scintillator belonging to the garnet family of crystals. It is characterized by an emission related to the radiative and allowed 5 d 1 4 f 1 → 4 f 2 transition in trivalent praseodymium ions. It has been shown that it has good scintillation qualities such as light output, energy resolution and fast decay times. There have been attempts to enhance the already good properties of LuAG:Pr such as optimizing annealing conditions, since this material has a potential to be used in Positron Emission Tomography (PET) detector systems. Previously reported studies show that there have been successful cases of improving the light yield and energy resolution. In this paper we show a detailed study of the non-proportionality and energy resolution in LuAG:Pr crystals that have been modified by partially substituting lutetium with yttrium and introducing intentional trace amounts of molybdenum co-doping. The measurements have been performed with varied shaping times to study the influence of long decay components on the scintillation parameters.

Preparation of dense Ta-LLZO/MgO composite Li-ion solid electrolyte: Sintering, microstructure, performance and the role of MgO

Cubic phase Li7La3Zr2O12 (LLZO), a member of the Li–Garnet family, is a promising solid electrolyte and has been widely studied in recent years. However, LLZO samples prepared via conventional ambient air sintering reported in the published literature often contain large grains with lower than desired (<94%) relative density. In this study, a non-contact method of co-firing with mother powder method is proposed to prepare high-quality Ta-doped LLZO–MgO composite ceramics. By sintering at 1150°C for 5 h, the ceramics can reach relative density of 98.2%, conductivity of 5.17 × 10−4 S cm−1 at 25 °C and fracture strength of ∼150 MPa. The sintered samples have uniform fine-grained microstructure and high critical current densities of 0.75–0.95 mA cm−2 at room temperature in Li–Li symmetry cell with Au modification. In addition, systematic sintering experiments and characterizations are conducted to explore the function of MgO in inhibiting the Ta-LLZO grain growth and its existing form inside the composite ceramics.

Structure and properties of hydrogrossular mineral series

AbstractThe hydrogrossular (HG) mineral series (Ca3Al2(SiO4)3−x(OH)4x; 0≤x≤3) are water‐bearing minerals found in the upper part of the Earth's mantle and as well as on its surface. They are vital to the planet's hydrosphere under different hydrothermal conditions. The composition and structure of this mineral series are important in geoscience and share many commonalities with cement and clay materials. Other than the end‐members of the series grossular (x=0) and katoite (x=3) which have a cubic garnet structure, the structures of the intermediate‐members are totally unknown. We used large‐scale ab initio modeling to investigate the structures and properties for HG series for x=0, 0.5, 1, 1.5, 2, 2.5, 3. Results indicate that for x&gt;0 and x&lt;3, the structures are tetragonal or nearly tetragonal, which partially justify that this garnet family is known to be cubic or pseudocubic. We also show that there are structural changes related to the disorder introduced with the composition mixing of SiO4 tetrahedra and AlO6 octahedra in the series. Based on the models constructed, the mechanical and interband optical properties of the HG series are calculated. For grossular and katoite, results are in good agreement with the available experimental data. The calculated electronic structure, total bond order explains the atomistic origin of the change in the compressibility of the series. Careful analysis of patterns of these results indicates that the series can be roughly divided into three regions: region I (x=0‐0.75), region II (x=0.75‐2.25), and region III (x=2.25‐3) with high, intermediate, and low Si/H ratio respectively. We also point out the inappropriateness of using the ill‐defined concept of treating O4H4 as a compressible structural unit in interpreting the structure and properties of HG series. Furthermore, the phonon spectra of grossular and katoite are calculated.

Study the Interface of Cathode Material and Li-La-Zr-O Thin Film Prepared at Low Temperature for All Solid State Li Battery

Switching from an organic polymer-based Li ion electrolyte to a ceramic Li ion electrolyte is expected to allow for the higher energy density, improve the safety and cycle lifetime. These, all solid state Li ion batteries can also be miniaturized, which will streamline the packing design. Among studied Li ion conductive solid electrolyte (1, 2) garnet family have recently gained lots of attention due to the high ionic conductivity and electrochemical stability at ambient temperature. Garnet-like structure, Li7La3Zr2O12 (LLZO) has shown comparable Li ion conductivity with the current Li ion electrolytes (3). However, the reported ionic conductivity of a thin film LLZO was three orders of magnitude lower compared to bulk phase (4). The main goal of the current research is to develop thin film solid electrolyte on the LiCoO2 electrode and investigate the interface. For this purpose, LLZO was fabricated using a liquid precursor technique. The Li-La-Zr nitrate solution was coated on the top surface of the LiCoO2 substrate for several times until the appropriate thickness (300 nm – 1 µm) is obtained. After each step of coating, the deposited precursor is dried and decomposed at 450 °C. Figure 1 shows cross section image of crack-free, flat, dense and homogenous solid electrolyte layer deposited on the surface of the LiCoO2. X-ray photoelectron spectroscopy (XPS) coupled with ion etching is used to understand the interface composition and thickness. Electrochemical impedance spectroscopy (EIS) was used to analyze and understand the electrolyte and interfacial resistance.

Solid State Electrolytes Based on Doped Li7La3Zr2O12 Garnets: Crystal Chemistry, Ion Transport and Implementation into Li Batteries

Solid-state batteries could greatly boost current Li-ion technologies; they are expected to endure tens of thousands recharges, pack 2-3 times more energy as well as being safe from combustion and non-toxic. However, a widespread application of solid-state batteries is still far from being achieved owing mainly to limitations of the solid electrolyte component. Key challenges are achieving high ionic conductivity-in the range of 1 mS/cm-, good interfacial contact with the electrodes and easy/cost efficient processing. Among ceramic electrolytes, the garnet family Li7La3Zr2O12 (LLZO) is one of the most promising because of its high lattice conductivity for Li ion and its wide electrochemical stability [1],[2]. Unfortunately, these garnet-type materials often show highly resistive grain boundaries and have proven difficult to process into dense ceramic bodies. In this presentation I will show our research on developing high-performance LLZO solid electrolytes. By using a wide variety of techniques, such as solid-state NMR, XRD, SEM and EIS, as well as DFT simulations, we investigate the role of crystal chemistry, doping and processing to the total conductivity and sintering properties of the ceramic electrolyte. I will particularly focus on the fundamental understanding and enhancementof ionic conductivity via substitutional doping of Li+ by Ga3+, which led to values as high as 1.3 mS/cm for Li6.55Ga0.15La3Zr2O12 at room temperature[3]. Alternative substitutions on the Zr4+ site can lead to a wider range of compositional possibilities and even higher conductivity values. The implementation of these LLZO garnet electrolytes into full cell devices, with LFP or LCO as cathode and Li metal as anode, will be also presented. Finally I will report on a novel solid electrolyte concept based on the combination of doped LLZO garnets and polymeric Li-ion conductors, such as polyethylene oxide (PEO). These ceramic-polymeric composites show great promise as solid electrolyte membranes given the superior mechanical and interfacial properties compared to pure ceramics. [1] R. Murugan, V. Thangadurai, W. Weppner. Angew. Chem. Int. Ed. 46, 7778-7781 (2007). [2] M. Nakayama, M. Kotobuki, H. Munakata, M. Nogamia and K. Kanamura. Phys. Chem. Chem. Phys., 14, 10008-10014 (2012). [3] Bernuy-Lopez, C.; Manalastas, Jr. W.; Lopez del Amo, J-M.; Aguadero, A.; Aguesse, F.; Kilner, J. A. Chemistry of Materials, 26, 3610 (2014).

Effects of Sublattice Symmetry and Frustration on Ionic Transport in Garnet Solid Electrolytes.

We use rigorous group-theoretic techniques and molecular dynamics to investigate the connection between structural symmetry and ionic conductivity in the garnet family of solid Li-ion electrolytes. We identify new ordered phases and order-disorder phase transitions that are relevant for conductivity optimization. Ionic transport in this materials family is controlled by the frustration of the Li sublattice caused by incommensurability with the host structure at noninteger Li concentrations, while ordered phases explain regions of sharply lower conductivity. Disorder is therefore predicted to be optimal for ionic transport in this and other conductor families with strong Li interaction.