Three-State Dielectric Switching within a Narrow Temperature Range in Isopropylammonium Lead Iodide, a One-Dimensional Perovskite with Polar Phase

The phenomenon of dielectric switching has garnered considerable
attention due to its potential applications in electronic and photonic
devices. Typically, hybrid organic–inorganic perovskites, HOIPs,
exhibit a binary (low–high) dielectric state transition, which,
while useful, represents only the tip of the iceberg in terms of functional
relevance. One way to boost the versatility of applications is the
discovery of materials capable of nonbinary switching schemes, such
as three-state dielectric switching. The ideal candidate for that
task would exhibit a trio of attributes: two reversible, first-order
phase transitions across three distinct crystal phases, minimal thermal
hysteresis, and pronounced, step-like variations in dielectric permittivity,
with a substantial change in its real part. Here, we demonstrate a
one-dimensional lead halide perovskite with the formula (CH3)2C(H)NH3)PbI3, abbreviated as ISOPrPbI3, that fulfills these criteria and demonstrates three-state
dielectric switching within a narrow temperature range of ca. 45 K.
Studies on ISOPrPbI3 also revealed the polar nature of
the low-temperature phase III below 266 K through pyrocurrent experiments,
and the noncentrosymmetric character of the intermediate phase II
and low-temperature phase III is confirmed via second harmonic generation
measurements. Additionally, luminescence studies of ISOPrPbI3 have demonstrated combined broadband and narrow emission properties.
The introduction of ISOPrPbI3 as a three-state dielectric
switch not only addresses the limitations posed by the wide thermal
gap between dielectric states in previous materials but also opens
new avenues for the development of nonbinary dielectric switchable
materials.

介电开关现象因其在电子与光子器件中的潜在应用而受到广泛关注。通常，有机-无机杂化钙钛矿（hybrid organic–inorganic perovskites, HOIPs）呈现出二元（低-高）介电态转变，尽管该特性具备应用价值，但就功能相关性而言仅为冰山一角。提升应用灵活性的途径之一，是开发可实现非二元开关机制的材料，例如三态介电开关。满足该研究需求的理想材料应具备三大特征：跨越三种不同晶相的两次可逆一级相变、极小的热滞后效应，以及介电常数实部分生显著的阶跃式变化且变化幅度可观。本文中，我们报道了一种化学式为(CH3)2C(H)NH3)PbI3（缩写为ISOPrPbI3）的一维卤化铅钙钛矿，其完全符合上述标准，并在约45 K的窄温度区间内实现了三态介电开关行为。对ISOPrPbI3的研究还通过热释电流实验，揭示了266 K以下低温相III的极性特性；同时借助二次谐波产生（second harmonic generation）测试，证实了中间相II与低温相III的非中心对称特征。此外，对ISOPrPbI3的发光研究表明其兼具宽带发射与窄带发射特性。将ISOPrPbI3作为三态介电开关材料，不仅解决了此前材料中介电态间热间隔过大的局限，更为非二元介电可开关材料的开发开辟了全新路径。