Interest on the nonlinear optical (NLO) switches that turn on/off the second-harmonic generation (SHG) triggered by the external stimulus (such as heat) have continuously grown, especially on the solid-state NLO switches showing superior stability, reversibility, and reproducibility. Herein, we discover (NH 4 ) 2 PO 3 F, as an entirely new solid-state NLO switch showing outstanding switch contrast and reversibility as well as strong SHG intensity (1.1 × KH 2 PO 4 (KDP)) and high laser-induced damage threshold (2.0 × KDP), undergoes a unique first-order phase transition that originates from a reversible hydrogen-bond rearrangement and needs to overcome an energy barrier. Accordingly, we put forward a strategy to continuously modify such an energy barrier by reducing the number of hydrogen bonds per unit cell via an isoelectronic replacement of NH 4 + by K + with a similar size yet incapability of providing any hydrogen bond. Consequently, K x (NH 4 ) 2−x PO 3 F (x = 0−0.3) exhibiting excellent switching performance are obtained. Remarkably, K x (NH 4 ) 2−x PO 3 F not only realizes a continuously tunable T c spanning from 270 to 150 K, representing the widest NLO switching temperature range ever known but also indicates the first solid-state NLO switch example with continuous T c . Intrinsically, such a T c decline depends on the weakening degree of the hydrogen-bonding interactions in the unit cell. These new insights will shed useful light on the future material design and open new application possibilities.
Conventional glass/carbon fiber-reinforced polymer (G/CFRP) composites have been widely used for infrastructure applications in the past decades. Nowadays, there is a trend to use cost-effective and ductile FRP composites such as polyester FRP (PFRP). This paper presents the results of an experimental investigation on the compressive behavior of concrete confined by PFRP jackets with low strength and high ductility. Twenty-seven PFRP confined plain concrete and nine unconfined plain concretes were tested. The considered experimental variables included concrete strength and PFRP thickness. Test results indicated that the PFRP jacket confinement increased the ductility of concrete to a great extent. However, the confinement on the enhancement in concrete ultimate compressive strength is limited. In addition, some existing stress–strain models were used to predict the ultimate stress and compared with the experimental results, and new confinement models were also proposed for PFRP-confined concrete
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