Understanding materials structures and how they give rise to their properties defines the central mission of Materials Science and Engineering. My dissertation work is focused on understanding the structure-property relationships in epitaxial thin films made of the prototypical relaxor ferroelectric 0.68PbMg1/3Nb2/3O3-0.32PbTiO3. While much work has been done on singe crystals of0.68PbMg1/3Nb2/3O3-0.32PbTiO3, the demand for device miniaturization calls for a thorough understanding of their structure-property relationships in thin film forms. As such, the work herein is primarily based on the development of epitaxial thin films as a new platform for investigating the behavior of nanoscale-polar structures under different conditions. First, I studied the epitaxial strain dependence of domain structures and dielectric and ferroelectric properties in 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 thin films using a combination of synchrotron-based X-ray diffuse-scattering, electrical measurements, and molecular-dynamics simulations. In this work, I observed that the diffuse-scattering patterns arising from the existence of polar nanodomains change from butterfly shapes to disc shapes as the epitaxial compressive strain increases due to the strain-induced polarization rotation. Even at the highest strains, the films exhibited persistent relaxor behavior due to the enhanced disorder in unit-cells with complex chemistries. After exploring the strain dependence, I studied the evolution of macroscopic phases under AC electric-fields using a synchrotron-based in operando X-ray microdiffraction technique. In this work, I observed that the polarization rotation is suppressed when the frequency of the AC electric-field becomes ultrasonic due to the limited kinetics for the growth of polar nanodomains. Building upon the understanding of strain- and electric-field-dependent structural evolutions and techniques to study them, I studied the relationship between polarization rotation and polar nanodomains using a multi-scale approach that probes the structural evolution in both the average unit-cells and polar nanodomains. I observed that the boundary between (pseudo-)rhombohedral and (pseudo-)tetragonal crystal structures of unit-cells is located in the same region of the strain-electric-field diagram as the boundary between ellipsoidal and cylindrical polar nanodomains, which are elongated along the <011> and [001], respectively. These results imply that polar nanodomains play a more direct role in polarization rotation than previously perceived and it is the strong coupling between the unit-cells and polar nanodomains that ultimately leads to the large electromechanical coupling in relaxor ferroelectrics. In addition to these, I studied the thickness-dependent evolution of polar nanodomains and various relaxor-phases using a combination of synchrotron-based X-ray diffuse-scattering, electrical measurements, and molecular-dynamics simulations. In this work, I constructed a thickness-temperature phase diagram, which was used as a guide to perform thickness- and temperature-dependent diffuse-scattering studies to probe the response of polar nanodomains to size effects. I observed that the distinguishing relaxor features of 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 disappear when the thickness is below the average size of the polar nanodomains. Ultimately, this implies that the compositional heterogeneities not only determine the size of the PNDs but also play a vital role in defining the stability of relaxors itself. Lastly, I demonstrated how the advanced understanding of structure-property relationships afforded by studies presented herein can lead to significant improvements of useful materials properties. Specifically, I explored the enhancement of capacitive energy storage properties in ion-bombarded 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 thin films. This work is based on the observation from the strain dependence that relaxor behavior is surprisingly persistent even in highly ferroelectric environments. The balance between persistent relaxor behavior and reduced electrical leakages in the presence of defects created by ion-bombardment with high-energy helium ions led to unprecedented capacitive energy storage performance. Overall, my work presented in this dissertation offers new understanding of structure-property relationships in relaxor ferroelectrics and demonstrates how such understanding can lead to new functionalities in old materials.

This dissertation investigates local government accountability in China. Three related chapters, combined, shed light on various issues in authoritarian accountability. Who holds local officials accountable: higher-level leaders (chapters 1 & 2) or the people (chapter 3)? How does the policy dynamic vary by domain: is policy formulation and execution different in the economic (chapter 1) versus the political realm (chapters 2 & 3)? How is accountability affected by stages in the policy process: is responsiveness greater or less during the experimentation (chapters 1 & 2) and implementation (chapters 2 & 3) phase? Each chapter relies on different methodological approaches: formal modeling (chapter1), qualitative historical analysis (chapter 2), and quantitative text analysis (chapter 3).

The first chapter examines how central leaders’ use of ambiguous guidelines shapes local officials’ incentive to undertake economic reform in the course of China’s policy experimentation. Contrary to the lessons of most principal-agent models, Chinese leaders have often provided local officials with ambiguous policy guidelines that do not clarify the boundaries of discretion. While ambiguity can offer local officials flexibility in policy implementation, it can also instill fear of punishment among possible transgressors and encourage preemptive self-censoring. Incorporating both perspectives, this article develops a formal model that analyzes a situation in which ambiguity allows flexibility for certain types of local officials while intimidating others. It argues that central leaders use ambiguity as a screening tool to encourage only “competent” local officials—those who have policy expertise for producing good outcomes—to choose a gray-area policy at their own risk, while deterring “incompetent” officials from doing so. The model is illustrated with a case study of state-owned enterprise restructuring in China. The argument is broadly applicable to interactions between all upper- and lower-level actors in the bureaucratic hierarchy.

The second chapter continues to explore central-local relations in China but turns to the realm of political reform, in an effort to bridge the large literature on policy experimentation and implementation. Studies of local governance in China often point to nimble experimentation but problematic implementation. To reconcile these competing images, it is useful to clarify the concepts of experimentation and implementation and see how they unfolded in one policy area. The history of China’s Open Government Information (OGI) initiative shows that the experimentation stage sometimes proceeds well and produces new policy options, but may falter if local leaders are unwilling to carry out an experiment. And the implementation stage often poses challenges, but may improve if the Center initiates new, small-scale experiments and encourages local innovation. This suggests that the experimentation and implementation stages are not so different when officials in Beijing and the localities have diverging interests and the Center is more supportive of a measure than local officials. The ups and downs of OGI, and also village elections, can be traced to the policy goal of monitoring local cadres, the central-local divide, and the pattern of support and opposition within the state.

The third chapter analyzes the implementation of the OGI policy, drawing attention to the role of citizens. How and when do opportunities for political participation through courts change under authoritarianism? Although China is better known for tight political control than for political expression, the 2008 OGI regulation ushered in a surge of political-legal activism. The article draws on an original dataset of 57,095 OGI lawsuits, supplemented by interview data and government documents, to show how a feedback loop between judges and court users shaped possibilities for political activism and complaint between 2008 and 2019. In contrast to the conventional explanation that authoritarian leaders crack down on legal action when they feel politically threatened, it finds that courts minted, defined and popularized new legal labels to cut off access to justice for the minority of super-active litigants whose lawsuits had come to dominate the OGI docket. This study underscores the power of procedural rules and frontline judges in shaping possibilities for political participation under authoritarianism.