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1. Structural origin of the weak germanate anomaly in lead germanate glass properties

   https://doi.org/10.1111/jace.18166  

   Alderman, Oliver L.; Hannon, Alex C.; Holland, Diane; Dupree, Ray; Feller, Steve (February 2022, Journal of the American Ceramic Society)
2. Topological model of alkali germanate glasses and exploration of the germanate anomaly

   https://doi.org/10.1111/jace.17102  

   Welch, Rebecca S.; Wilkinson, Collin J.; Shih, Yueh‐Ting; Bødker, Mikkel S.; DeCeanne, Anthony V.; Smedskjaer, Morten M.; Huang, Liping; Affatigato, Mario; Feller, Steve A.; Mauro, John C. (April 2020, Journal of the American Ceramic Society)

   Abstract Germanate glasses are of particular interest for their excellent optical properties as well as their abnormal structural changes that appear with the addition of modifiers, giving rise to the so‐calledgermanate anomaly. This anomaly refers to the nonmonotonic compositional scaling of properties exhibited by alkali germanate glasses and has been studied with various spectroscopy techniques. However, it has been difficult to understand its atomic scale origin, especially since the germanium nucleus is not easily observed by nuclear magnetic resonance. To gain insights into the mechanisms of the germanate anomaly, we have constructed a structural model using statistical mechanics and topological constraint theory to provide an accurate prediction of alkali germanate glass properties. The temperature onsets for the rigid bond constraints are deduced from in situ Brillouin light scattering, and the number of constraints is shown to be accurately calculable using statistical methods. The alkali germanate model accurately captures the effect of the germanate anomaly on glass transition temperature, liquid fragility, and Young's modulus. We also reveal that compositional variations in the glass transition temperature and Young's modulus are governed by the O–Ge–O angular constraints, whereas the variations in fragility are governed by the Ge–O radial constraints. 

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3. Rb2Co1.85Ge1.15O6: The First Quaternary, Noncentrosymmetric Rubidium Cobalt Germanate

   https://doi.org/10.1007/s10870-020-00868-9  

   Usman, Mohammad; Smith, Mark D.; zur Loye, Hans-Conrad (October 2020, Journal of Chemical Crystallography)

   null (Ed.)
4. Dynamic Luminescence of Lead-Doped Calcium Zinc Germanate Clinopyroxene for Multimode Anticounterfeiting

   https://doi.org/10.1021/acsami.3c16016  

   Yang, Zishen; Spencer, Levi D; Zhang, Huixin; Burmood, Zachary L; Putta, Anjaneyulu; Jiang, Chaoyang (April 2024, ACS Applied Materials & Interfaces)

   Anticounterfeiting plays an essential role in authenticating genuine documents and combating forged products. To further advance the anticounterfeiting technology, there is a strong demand to design new functional materials with unique properties that will be appropriate for making multimode complex security labels. Recently, dynamic security labels have emerged as a new type of advanced anticounterfeiting method as they can hold a much higher security level than the traditional static ones. In this work, we report that calcium zinc germanate (CZGO) clinopyroxenes doped with lead ions have several interesting optical properties, such as dynamic fluorescence, long persistent luminescence, and photochromism. We find that the concentration of lead dopants can significantly impact the reaction kinetics as well as the crystallinity and luminescence properties of CZGO phosphors. By fully utilizing these unique properties, we have successfully fabricated several security labels with multilevel information encoding and dynamic optical performance. The combination of multimode and dynamic luminescence makes these labels extremely challenging to illegally duplicate. With further optimization, this lead-doped CZGO clinopyroxene can be well-integrated into modern anticounterfeiting techniques that will generate highly secure anticounterfeiting labels to combat fake products. 

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5. Observation of Unconventional Dynamics of Domain Walls in Uniaxial Ferroelectric Lead Germanate

   https://doi.org/10.1002/adfm.202000284  

   Bak, Ohheum; Holstad, Theodor_S; Tan, Yueze; Lu, Haidong; Evans, Donald_M; Hunnestad, Kasper_A; Wang, Bo; McConville, James_P_V; Becker, Petra; Bohatý, Ladislav; et al (March 2020, Advanced Functional Materials)

   Abstract Application of scanning probe microscopy techniques such as piezoresponse force microscopy (PFM) opens the possibility to re‐visit the ferroelectrics previously studied by the macroscopic electrical testing methods and establish a link between their local nanoscale characteristics and integral response. The nanoscale PFM studies and phase field modeling of the static and dynamic behavior of the domain structure in the well‐known ferroelectric material lead germanate, Pb₅Ge₃O₁₁, are reported. Several unusual phenomena are revealed: 1) domain formation during the paraelectric‐to‐ferroelectric phase transition, which exhibits an atypical cooling rate dependence; 2) unexpected electrically induced formation of the oblate domains due to the preferential domain walls motion in the directions perpendicular to the polar axis, contrary to the typical domain growth behavior observed so far; 3) absence of the bound charges at the 180° head‐to‐head (H–H) and tail‐totail (T–T) domain walls, which typically exhibit a significant charge density in other ferroelectrics due to the polarization discontinuity. This strikingly different behavior is rationalized by the phase field modeling of the dynamics of uncharged H–H and T–T domain walls. The results provide a new insight into the emergent physics of the ferroelectric domain boundaries, revealing unusual properties not exhibited by conventional Ising‐type walls. 

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