HfO₂, a simple binary oxide, exhibits ultra-scalable ferroelectricity integrable into silicon technology. This material has a polymorphic nature, with the polar orthorhombic (Pbc2₁) form in ultrathin films regarded as the plausible cause of ferroelectricity but thought not to be attainable in bulk crystals. Here, using a state-of-the-art laser-diode-heated floating zone technique, we report the Pbc2₁ phase and ferroelectricity in bulk single-crystalline HfO₂:Y as well as the presence of the antipolar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti)polar crystallographic signatures and abundant 90°/180° ferroelectric domains in addition to switchable polarization with negligible wake-up effects. Density-functional-theory calculations indicate that the yttrium doping and rapid cooling are the key factors for stabilization of the desired phase in bulk. Our observations provide insights into the polymorphic nature and phase control of HfO₂, remove the upper size limit for ferroelectricity and suggest directions towards next-generation ferroelectric devices.

HfO ₂是一种简单的二元氧化物，具有可集成到硅技术中的超可扩展铁电性。这种材料具有多晶型性质，超薄膜中的极性正交（Pbc 2 ₁）形式被认为是铁电性的可能原因，但被认为在块状晶体中无法实现。在这里，我们使用最先进的激光二极管加热浮动区技术，报告了块状单晶 HfO _{2 :Y 中的}Pbc 2 ₁相和铁电性以及反极性Pbca的存在不同 Y 浓度的相。中子衍射和原子成像展示了（反）极性晶体学特征和丰富的 90°/180° 铁电畴，以及可忽略唤醒效应的可切换极化。密度泛函理论计算表明，钇掺杂和快速冷却是稳定所需相的关键因素。我们的观察提供了对 HfO ₂的多晶型性质和相位控制的见解，消除了铁电体的尺寸上限，并为下一代铁电体器件提出了方向。