Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering.

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi0.5(Na0.8K0.2)0.5TiO3-xBi0.2Sr0.7TiO3 (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature Tm and inducing the formation of highly dynamic polar nano-regions. In addition, the Tm shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered Tm with relaxor properties synergistically contribute to a high Pmax and low Pr, improving the breakdown strength with BST and resulting in a high recoverable energy density Wrec of 0.81 J/cm3 and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Effects of the loss of mismatch repair genes on single-strand annealing between divergent sequences in Saccharomyces cerevisiae.

Eukaryotic genomes contain many duplicated genes closely located with each other, such as the hexose transporter (HXT) genes in Saccharomyces cerevisiae. They can potentially recombine via single-strand annealing (SSA) pathway. SSA between highly divergent sequences generates heteroduplex DNA intermediates with many mismatches, which can be corrected by mismatch repair (MMR), resulting in recombinant sequences with a single junction point. In this report, we demonstrate that SSA between HXT1 and HXT4 genes in MMR-deficient yeast cells produces recombinant genes with multiple-junctions resulting from alternating HXT1 and HXT4 tracts. The mutations in MMR genes had differential effects on SSA frequencies; msh6Δ mutation significantly stimulated SSA events, whereas msh2Δ and msh3Δ slightly suppressed it. We set up an assay that can identify a pair of recombinant genes derived from a single heteroduplex DNA. As a result, the recombinant genes with multiple-junctions were found to accompany genes with single-junctions. Based on the results presented here, a model was proposed to generate multiple-junctions in SSA pathway involving an alternative short-patch repair system.

Analyses of DNA double-strand break repair pathways in tandem arrays of HXT genes of Saccharomyces cerevisiae.

Eukaryotic genomes contain numerous homologous repeat sequences including redundant genes with divergent homology that can be potential recombination targets. Recombination between divergent sequences is rare but poses a substantial threat to genome stability. The hexose transporter (HXT) gene family shares high sequence similarities at both protein and DNA levels, and some members are placed close together in tandem arrays. In this study, we show that spontaneous interstitial deletions occur at significantly high rates in HXT gene clusters, resulting in chimeric HXT sequences that contain a single junction point. We also observed that DNA double-strand breaks created between HXT genes produce primarily interstitial deletions, whereas internal cleavage of the HXT gene resulted in gene conversions as well as deletion products. Interestingly, interstitial deletions were less constrained by sequence divergence than gene conversion. Moreover, recombination-defective mutations differentially affected the survival frequency. Mutations that impair single-strand annealing (SSA) pathway greatly reduced the survival frequency by 10-1,000-fold, whereas disruption of Rad51-dependent homologous recombination exhibited only modest reduction. Our results indicate that recombination in the tandemly repeated HXT genes occurs primarily via SSA pathway.