Thermomechanical and Interfacial Properties of Lead‐Free Bi ₂ O ₃ −ZnO−B ₂ O ₃ Glasses for Hermetic Sealing Applications

ABSTRACT Lead‐free bismuthate‐based sealing glasses are of growing interest for environmentally sustainable electronic and packaging applications. In this work, lead‐free Bi 2 O 3 –ZnO–B 2 O 3 glasses were modified through two distinct substitution routes—BaO replacing B 2 O 3 and SrO exchanging for BaO—to evaluate their suitability for glass‐to‐metal sealing. BaO‐for‐B 2 O 3 substitution reduced glass transition temperature (330→325°C) and increased coefficient of thermal expansion (13.0→14.1 ppm/K) due to network depolymerization, yielding a low sealing range of 505–550°C, but decreasing nanohardness (4.9→4.6 GPa) and elastic modulus (69→63 GPa). SrO‐for‐BaO exchange maintained nearly constant density and mechanical properties, with only minor fluctuations in thermomechanical properties, while supporting a sealing window of 520–580°C. Raman spectra confirmed increasing nonbridging oxygen formation in BaO‐substituted glasses, whereas SrO exchange induced only subtle structural shifts. Both systems formed diffusion‐bonded interfacial layers (<2 µm) with 304 stainless steel and showed thermal expansion compatibility (mismatch <10%), validating hermetic sealing. These results establish BaO‐for‐B 2 O 3 substitution as advantageous for low‐temperature sealing and SrO‐for‐BaO exchange as beneficial for stabilizing thermomechanical properties, offering complementary design strategies for sustainable lead‐free sealing glasses.