Conductive mechanism of reduced lead silicate glass for micro‐channel plate

Abstract

Lead silicate glasses reduced by hydrogen have the characteristics of conductivity like semiconductors and surface secondary electron emission. Therefore, lead silicate glass is the important material of microchannel plate (MCP) for electron multiplier element. The change of bulk resistance (BR) of lead silicate glass (LSG) with hydrogen reducing time and temperature, and hydrogen flow was investigated. The effect of various hydrogen‐reducing parameters on BR is firstly decreasing, then keeping level, and finally increasing. The tendency presents V‐shaped curve. By analyzing the surface composition and morphology of LSG, it is found that the quantity and aggregation state of lead and bismuth are the key factors determining the conductivity of LSG. It is indicated that the electrical conduction is derived from ions and electrons of LSG. The conductive mechanism, however, is different in different stages in the V‐shaped curve. The discovery of V‐shape curve and the conduction mechanism at different stages have important theoretical guiding significance for the fabrication of microchannel plates.

Structure and disorder in Pb‐Na metasilicate (PbO:Na2O:2SiO2) glasses: A view from high‐resolution 17O solid‐state NMR

“…Due to the overlap among mixed NBO peaks, several constraints for simulations were tested. First, for the simulation of MAS NMR spectra, the peak positions and widths (FWHM) of 4 Here, as number Pb atoms near NBO increases, its peak position is expected to shift nonlinearly (see SI-2 for the details), which is consistent with the observation in 2D 3QMAS NMR spectra where 1 Na 2 Pb-O-Si is apparently located close to 3 Pb-O-Si than 2 Na 1 Pb-O-Si. The peak widths of mixed-NBO peaks were constrained to be the statistical average of end-member peaks: the width of 2 Na 1 Pb-O-Si is 27 ppm and that of 1 Na 2 Pb-NBO is 33 ppm.…”

“…In this study, the quantitative fractions of each oxygen species (i.e., mixed NBO, Na-O-Si, Pb-O-Si, and Si-O-Si) in PbO-Na 2 O-SiO 2 glasses with varying Pb content were estimated from the analysis of both 1D and 2D 17 O NMR spectra ( Figure 5). The 17 O MAS spectra and total isotropic projection of 17 O 3QMAS NMR spectra were simulated based on the assumption of four NBO sites (i.e., 4 Na, 2 Na 1 Pb, 1 Na 2 Pb, and 3 Pb) 73,74,83 and one BO site. Due to the overlap among mixed NBO peaks, several constraints for simulations were tested.…”

“…For example, a slight preference of the dissimilar pair (i.e., [Na,Ca]-NBO) in Na-Ca silicate/ aluminosilicate glasses stems from the charge difference between non-framework cations, given the similarity of their radii (i.e., Na + : ~1.02 Å, Ca 2+ : ~1.0 Å). 73,82 The ionic radius of Pb 2+ , with a Pb 2+ coordination number near that in glasses of metasilicate composition (~50 mol% of SiO 2 ) is ~0.98 Å (for [4] Pb 2+ ). 94 Thus, considering similar ionic radii (~1 Å), the observed prevalence of Pb 2+ -Na + , favoring chemical order, can mainly be attributed to the difference in charge of nonframework cations.…”

“…Lead (Pb)-bearing silicate glasses are among the key ceramic materials that have diverse industrial applications, such as optics, 1 optoelectronic devices, 2 and electron multipliers. 3,4 Since ~1400 B.C., Pb-bearing multicomponent oxide glasses such as flint glasses and lead crystal glasses have been widely used (e.g., 5,6 ), mainly due to their low melting temperature (~900-1100 K). 7 In part because of their excellent glass-forming ability, glasses consisting of higher PbO concentration (i.e., PbO/SiO 2 > 2) can be easily synthesized via the conventional melt-quenching method (e.g., [8][9][10][11] ).…”

“…This indicates a more prominent configurational disorder in the glass network around Pb-NBO (i.e., the number of possible configurations and complexity in Pb coordination environments). We note that oxygen sites linking to Pb (e.g., Pb-O-Si) can be due to various oxygen environments with [4] Si and more than one [3,4] Pb depending on the composition, and thus, represents [n] Pb- [m] O- [4] Si . While the oxygen peaks in the spectra for end-member glasses were unambiguously assigned to Na-O-Si and Pb-O-Si (see above), there is no previous report on the oxygen NMR characteristics of mixed-NBO peak for Pb-Na silicate glasses.…”