Figure 2 shows a cluster analysis based on keyword co-occurrence, the results of which were trimmed to a selection of seven clusters, with larger cluster modules

representing hot research topics about family firms. The specific results are shown in Table 1. In terms of size, the seven clusters all cover at least 10 nodes, with S values⁵ larger than 0.778, reflecting reasonable clustering and clear-cut themes. From these clustering results, hot research topics about family firms include governance of family firm groups, a definition of family firms, relevant research approaches, and family visions, as well as technological innovation, strategic decision-making, entrepreneurship, and family firm agencies. In combination with these clustering results and intercluster relationships, we summarizes and discusses the following hot research topics about family firms in other countries:

Family firm groups and family firms. Cluster 0 and Cluster 1 are discussed together, mainly including subclusters such as corporate governance, control, and firm performance. Family firms in WoS have a long history. One characteristic that distinguishes family firms between western developed countries and China is the establishment of family councils. Family councils can lead family firm groups and family funds, specify the duties of family members, achieve a smooth succession of family firms, and maintain harmony within families [9] . This not only guarantees ownership and control by family members [10] [11] and continuity of family interests, but also enables family firms to meet the challenges of various risks and opportunities through diversified development.

Future prospect of family firms and challenges they will face. This cluster includes subclusters such as conservative attitudes about the future, strategic management, and future challenges for enterprises. The risk preferences of family owners play a decisive role in the future development and direction of enterprises, which is also one of the characteristics distinguishing family firms from non-family firms [12] . The strategic management and grasp of future opportunities will influence long-term development of family firms [13] .

Innovation of family firms. This cluster contains the subclusters of technological innovation, risk-taking, and entrepreneurial orientation. In studies of firm innovation, different ownership structures of family firms affect their risk preferences and thus their research and development (R&D) investments. However, there are different results of how family involvement impacts R&D of family firms. Some scholars believe that family firms prefer to pursue established strategies over long periods of time and providing permanent R&D investments [14] . Other scholars posit that enterprises tend to make relatively conservative strategic decisions to avoid the loss of family interests, which can hinder investment in R & D [15] . For scholars, it is worth further discussing the reasons for such contradictory findings.

The entrepreneurship and strategies of family firms. Cluster 4 and Cluster 5 are discussed together. These two clusters contain the subclusters of entrepreneurship, success, socioemotional wealth, and business diversification of family firms. Entrepreneurs lead the market economy, and entrepreneurship is the soul of entrepreneurs, and it play a prominent role in family firms, which often have an entrepreneurial base [16] [17] . The complementary strategic behavior and entrepreneurial activities of family firms can help them maximize wealth.

Strategic entrepreneurship also becomes a hot research topic in international academic circles. As an example, the Strategic Management Society of the United States launched a magazine, the Strategic Entrepreneurship Journal. To maximize inheritance, family firms depend on family entrepreneurship. Inheritors internalize their families’ spirit through a series of strategic entrepreneurial actions, such as keeping up with the times, to guarantee their businesses’ long-term success [18] .

Agencies of family firms. Continuous development of family firms restricts their ability of relying solely on family members, an issue that can be solved by hiring professional managers, though this solution will cause agency conflict. Scholars have focused on how to settle the question of information asymmetry when family members and senior management teams have different goals [19] .

Figure 3 shows the seven clusters representing the hot research topics on Chinese family firms. Table 2 shows that the seven clusters all exceed 10, with all S

values above 0.714. Based on clustering results and intercluster relationships, we integrated the seven clusters and discuss them in four areas.

Family control. Cluster 0 and Cluster 6 are considered family control. Even though the study of family firms is from different perspectives, the reason why the two clusters having same laber is that they both include “family control” in their keywords. In these two clusters, “family control” ranked first among subcluster names. Considering the mean year and size of the clusters, research on Chinese family firms focuses on family control, an initial characteristic of family firms that can persist for a long time [20] [21] [22] . Additional research on family control has prompted a shift of focus from antagonism between families and businesses to exploring how to settle conflicts between families and businesses (socioemotional wealth) and how to guarantee long-term development of businesses (willingness of succession).

Enterprise growth and enterprise culture. Cluster 1 and Cluster 5 address internal business governance. When family firms protect the interests of the family, business growth can be affected to a certain extent. As a result, many family firms are confused about the way to achieve a more harmonious agency relationship between family members and external members through system innovation, in order to realize smooth business growth [23] [24] . Construction of an enterprise culture is important to guarantee its long-term development. In this regard, Chinese family firms are quite different from non-family firms [25] [26] , which need to focus on how to establish a successful enterprise system and incentive policies to recharacterize family characteristics for competitive advantage.

Contractual governance and altruism. Cluster 2 and Cluster 3 are concerned with the altruism of family firms, combining family interests at an initial stage of development to create competitive advantage with continuous business development. However, the pursuit of the whole family benefits may cause several agency problems [27] . Researchers have widely accepted that family altruism constitutes an important characteristic of family firms. A large number of studies have been conducted to examine the effect of altruism on these firms. These studies mainly focus on the relationship between altruism and agency. Altruism facilitates family employees to become co-owners of a firm. Co-ownership binds the interests of family firm owners and their family employees together [28] , thereby reducing the cost of contractual governance [29] . Altruism enhances communication and collaboration among family members and reduces information asymmetry between the owners of family firms and family employees, which could increase the effectiveness of informal contractual governance [30] .

To sum up, the effect of altruism on the principal-agent of family firms is neither purely positive nor negative, and the effect of the moral elements in this relationship cannot be underestimated. Family firms should thoroughly understand altruism and reduce the cost of contractual governance.

Social capital. Relationships are highly valued in Chinese society, and family firms in such a relationship-based society will inevitably have to weigh the law of demand against the law of human relations in the process of management and development [31] [32] . For family firms, family is the core of social capital, and Chinese family firms need to consider how to break through traditional family-oriented ideas to build more scientific governance structures within existing social networks to achieve transformational development.

1) The burst terms that have lasted the longest

Figure 4 has shown that burst terms of WoS. Through detection of burst terms in WoS, we found that “gender” merged first (in 1988) and lasted the longest (until 2007). Scholars first discussed and analyzed the concept of “family” when they began to study family firms. Family firms largely developed from small businesses run by families, in which male and female members played different roles, thus forming different enterprise development patterns [33] . Because of different traditions and cultural backgrounds, the division of power and management of labor between male and female family members have attracted the long-term attention of scholars. In addition, succession in family firms is also a key point that distinguishes family firms from non-family firms. As the economic development collides with traditional culture, family controllers have caused problems of inheritance and choosing between male and female successors [34] [35] . Clearly, gender has influenced firms’ internal mechanisms.

2) The strongest burst terms

The hot keyword “socioemotional wealth,” which burst in 2014, appeared late but had the highest strength of 11.81. In their theory of socioemotional wealth, Gomezmejia et al. [36] pointed out that socioemotional wealth is an important element in the governance and strategy of family firms. In studying family firms,

scholars have always disputed the nature of the conflict between family and corporate interests. The theory of socioemotional wealth provides a new perspective for the study of family firms, solving the long-standing problem that scholars interpret family interests without also considering corporate and economic interests. Since research on socioemotional wealth is in its initial stage, it remains just a qualitative concept at present [37] . Future research should specify the structural dimensions of this theory and improve its measurement methods from a quantitative perspective, to more clearly show the influence of socioemotional wealth on family firms.

3) The burst terms that appeared last

The hot keyword “development investment,” which burst in 2015, is the last burst term to be considered. Some existing literatures focused on innovation and investment development of family firms, which enable them to maintain competitive advantage. Although the scale, financing, and technology of family firms can make progress difficult, many firms seem willing to undertake entrepreneurial development to gain competitive advantage [38] .

From the analysis of these three burst terms of WoS as shown in Figure 4, we find that family firms have existed for a longer period of time in western developed countries than in China. Initially, scholars of WoS studied the structure and orientation of insiders. The introduction of professional managers has caused a degree of conflict with family members and has affected the management of enterprises, which attracted attentions of scholars. Additionally, the hot keywords “altruism” and “socioemotional wealth” indicate that the theoretical basis for family firms has shifted from altruism to socioemotional wealth. The theory of socioemotional wealth unravels contradictions between families and firms from a new perspective, providing theoretical support for a balance between family interests and corporate interests. On this basis, the research of enterprise investments provides a new direction for the long-term development of enterprises.

1) The burst terms lasting the longest

Figure 5 has shown that burst terms of CSSCI. In studies of Chinese family firms, the hot keyword “intergenerational succession” lasted for the longest time after it burst in 2008 (it remains a burst term). Chinese family firms have only developed for a short time, and the founders of many family firms began to face the problem of succession in recent years. Despite such diverse factors as traditional culture, growth, industry features, and scale, “carrying on the parents’ cause” is a major form of succession in many Chinese family firms. The historical family culture of China will make the family model a major choice for enterprises [39] , but company founders may hesitate due to many problems involved in carrying on the parents’ cause. This generates a “pan-family” succession model, expanding the range of successors to cover relatives, friends, and even professional managers [40] . The problems of power and the allocation of business interests in

“pan-families” are worth further discussion.

2) The strongest burst terms

The hot keyword “family control,” which is the strongest burst term, appeared late, in 2013. Scholars in China have not achieved consensus on the definition of family firms, but all commonly recognize definitions involving family control and family ownership. Ownership and control generally are highly centralized in Chinese family firms, which have a more prominent interest conflict with minor shareholders [41] [42] . How to balance family interests and corporate interests to guarantee long-term business development is an urgent problem that Chinese family firms have to solve now.

3) The burst terms that appeared last

The hot keywords “family involvement” and “family control,” which began in 2013, are the latest burst terms. “Family control” is not only the last, but also the strongest burst term. It clearly shows the respect for authority in Chinese family firms, under the influence of the unique Chinese family culture. However, such control can also cause prominent problems in enterprise R&D, performance, and succession [43] [44] . In addition, the characteristic of differential sequence pattern [45] in Chinese social relationships leads to the focus of makes Chinese scholars on family authority.

A burst analysis of three Chinese keywords in Figure 5 indicates that 2008 was a dividing year for research on family firms in China. Earlier, the major research focused on enterprises, including internal governance and enterprise transitions. In other words, family firms were just a type of organization, not highlighting the family characteristics. After the financial crisis in 2008, scholars began to shift their attention to the significant role of family. Because Chinese family firms started late, most of them have just recently entered the stage of succession. Scholars, following this trend, are becoming interested in intergenerational succession and the agency of professional managers.